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1.
Francisco Barros Luis M. Delgado Donato del Camino Pilar de la Peña 《Pflügers Archiv : European journal of physiology》1992,422(1):31-39
Hyperpolarization of patch-perforated GH3 rat anterior pituitary cells in high-K+ Ca2+-free medium reveals an inwardly rectifying K+ current. This current showed potential-dependent activation and inactivation kinetics, complete inactivation during strong hyperpolarization and rectification at depolarized potentials. The current was blocked by millimolar concentrations of external Cs+, Ba2+, Cd2+ and Co2+, but it was almost insensitive to tetraethylammonium, 4-aminopyridine and two dihydropyridines, nisoldipine and nitrendipine. Verapamil and methoxyverapamil produced a strong and reversible inhibition of the current. In the presence of 100 nM thyrotropin-releasing hormone (TRH), the current was reduced. This reduction was increased by holding the cell at more negative potentials and was accompanied by a shift in steady-state voltage dependence of inactivation towards more positive voltages. Furthermore, the current slowly returned to the initial levels upon washout. Treatment of the cell with the protein phosphatase inhibitor okadaic acid increased the magnitude of the inhibition caused by TRH. Moreover, the current did not return towards the control level during a 30-min washout period. It is concluded that protein phosphatases participate in modulation of the GH3 cell inwardly rectifying K+ channels by TRH. Furthermore, these data indicate that either a protein phosphatase or a factor necessary for its activation is lost under whole-cell mode, which could account for the permanent reduction of the current in response to TRH. 相似文献
2.
Francisco Barros Carlos Villalobos Javier García-Sancho Donato del Camino Pilar de la Peña 《Pflügers Archiv : European journal of physiology》1994,426(3-4):221-230
Exposure of GH3 rat anterior pituitary cells to cholera toxin for 2–4 h significantly increased the thyrotropin-releasing-hormone(TRH)-induced inhibition of the inwardly rectifying K+ current studied in patchperforated voltage-clamped cells. On the other hand, the current reduction became almost totally irreversible after washout of the neuropeptide. Comparison of the effects elicited by the toxin with those of 8-(4-chlorophenylthio)-cAMP or forskolin plus isobutylmethylxanthine indicated that, although the irreversibility may be due, at least in part, to elevations of cAMP levels, the enhancement of the TRH-induced inhibition of the current is not mediated by the cyclic nucleotide. Only reductions on the inwardly rectifying K+ current, but not those elicited by TRH on voltage-dependent Ca2+ currents, were increased by the treatment with cholera toxin. In current-clamped cells showing similar rates of firing, the second phase of enhanced action-potential frequency induced by TRH was also significantly potentiated by cholera toxin. Measurements of [Ca2+]i oscillations associated with electrical activity, using video imaging with fura-2-loaded cells, demonstrated that cholera toxin treatment causes a clear reduction of spontaneous [Ca2+]i oscillations. However, this did not prevent the stimulatory effect of TRH on oscillations due to the action potentials. In cholera-toxin-treated cells, the steady-state, voltage dependence of inactivation of the inward rectifier was shifted by nearly 20 mV to more negative values. These data suggest that the inwardly rectifying K+ current plays an important role in maintenance of the resting K+ conductance in GH3 cells. Furthermore, the TRH-induced reductions on this current may be an important factor contributing to the increased cell excitability promoted by the neuropeptide. 相似文献
3.
P. Komwatana A. D. Conigrave L. Delbridge J. A. Young D. I. Cook 《Pflügers Archiv : European journal of physiology》1994,426(3-4):320-327
We have used whole-cell patch-clamp techniques to study the conductances in the plasma membranes of human parathyroid cells. With a KCl-rich pipette solution containing Ca2+ buffered to a concentration of 0.1 mol/l, the zero current potential was –71.1±0.5 mV (n=19) and the whole-cell current/ voltage (I/V) relation had an inwardly rectifying and an outwardly rectifying component. The inwardly rectifying current activated instantaneously on hyperpolarization of the plasma membrane to potentials more negative than –80 mV, and a semi-logarithmic plot of the reversal potential of the inward current (estimated by extrapolation from the range in which it was linear) as a function of extracellular K+ concentration ([K+]o) revealed a linear relation with a slope of 64 mV per decade change in [K+]o, which is not significantly different from the Nernstian slope, demonstrating that the current was carried by K+ ions. The conductance exhibited a square root dependence on [K+]o as has been observed for inward rectifiers in other tissues. The current was blocked by the presence of Ba2+ (1 mmol/l) or Cs+ (1.5 mmol/l) in the bath. The outwardly rectifying current was activated by depolarization of the membrane potential to potentials more positive than –20 mV. It was inhibited by replacement of pipette K+ with Cs+, indicating that it also was a K+ current: it was partially (42%) blocked when tetraethylammonium (TEA+, 10 mmol/l) was added to the bath. The outwardly rectifying, but not the inwardly rectifying K+ current, was regulated by intracellular free Ca2+ concentration ([Ca2+]i) such that increasing [Ca2+]i above 10 nmol/l inhibited the outwardly rectifying current, the half-maximum effect being seen at 1 mol/l. Since it is known that increases in [Ca2+]o produce increases in [Ca2+]i, and that they depolarize parathyroid cells by reducing the membrane K+ conductance, we suggest that it is the reduction of the outwardly rectifying K+ conductance by increases in [Ca2+]i which is responsible for the reduction in K+ conductance seen when [Ca2+]o is increased. 相似文献
4.
F. Barros Donato del Camino Luis A. Pardo Teresa Palomero Teresa Giráldez Pilar de la Peña D. del Camino 《Pflügers Archiv : European journal of physiology》1997,435(1):119-129
Reduction of an inwardly rectifying K+ current by thyrotropin-releasing hormone (TRH) and caffeine has been considered to be an important determinant of electrical
activity increases in GH3 rat anterior pituitary cells. However, the existence of an inwardly rectifying K+ current component was recently regarded as a misidentification of an M-like outward current, proposed to be the TRH target
in pituitary cells, including GH3 cells. In this report, an inwardly rectifying component of K+ current is indeed demonstrated in perforated-patch voltage-clamped GH3 cells. The degree of rectification varied from cell to cell, but both TRH and caffeine specifically blocked a fraction of
current with strong rectification in the hyperpolarizing direction. Use of ramp pulses to continuously modify the membrane
potential demonstrated a prominent blockade even in cells with no current reduction at voltages at which M-currents are active.
Depolarization steps to positive voltages at the maximum of the inward current induced a caffeine-sensitive instantaneous
outward current followed by a single exponential decay. The magnitude of this current was modified in a biphasic way according
to the duration of the previous hyperpolarization step. The kinetic characteristics of the current are compatible with the
possibility that removal from inactivation of a fast-inactivating delayed rectifier causes the hyperpolarization-induced current.
Furthermore, the inwardly rectifying current was blocked by astemizole, a potent and selective inhibitor of human ether-á-go-go -related gene (HERG) K+ channels. Along with other pharmacological and kinetic evidence, this indicates that the secretagogue-regulated current is
probably mediated by a HERG-like K+ channel. Addition of astemizole to current-clamped cells induced clear increases in the frequency of action potential production.
Thus, an inwardly-rectifying K+ current and not an M-like outward current seems to be involved in TRH and caffeine modulation of electrical activity in GH3 cells.
Received: 15 May 1997 / Received after revision and accepted: 24 July 1997 相似文献
5.
Akiko Itoh Shunji Ueda Yasunobu Okada 《Pflügers Archiv : European journal of physiology》1994,428(5-6):468-475
K+ conductance species in a human intestinal epithelial cell line (Intestine 407) were studied in connection with their sensitivities to an intestinal secretagogue, histamine, using the tight-seal whole-cell patch-clamp technique. Applications of positive command pulses rapidly induced outward K+ currents. The conductance became progressively larger with increasing command voltages, exhibiting an outwardly rectifying current voltage relation. Inward K+ currents were also rapidly activated upon applications of hyperpolarizing pulses at potentials negative to the equilibrium potential of K+ (E K), and the conductance inwardly rectified. Application of a Ca2+ ionophore, ionomycin, brought about activation of additional K+ currents. An inhibitor of protein kinase C, polymyxin B, did not affect the ionomycin-induced response. Histamine (10–200 μM) also activated a similar K+ current which was abolished by cytosolic Ca2+ chelation. Under conditions where Ca2+ mobilization was minimized, histamine was found to significantly augment inwardly rectifying K+, but suppress outwardly rectifying K+, currents. Polymyxin B blocked these effects of histamine. An activator of protein kinase C, 1-oleoyl-2-acetylglycerol, mimicked the histamine effects. It is concluded that the intestinal epithelial cell has three distinct types of K+ conductance and that histamine modulates not only Ca2+-activated K+ conductance via Ca2+ mobilization, but also inward- and outward-rectifier K+ conductances via activation of protein kinase C. 相似文献
6.
Carlos Villalobos Javier García-Sancho 《Pflügers Archiv : European journal of physiology》1996,431(3):371-378
Caffeine, a well known facilitator of Ca2+-induced Ca2+ release, induced oscillations of cytosolic free Ca2+ ([Ca2+]i) in GH3 pituitary cells. These oscillations were dependent on the presence of extracellular Ca2+ and blocked by dihydropyridines, suggesting that they are due to Ca2+ entry through L-type Ca2+ channels, rather than to Ca2+ release from the intracellular Ca2+ stores. Emptying the stores by treatment with ionomycin or thapsigargin did not prevent the caffeine-induced [Ca2+]i oscillations. Treatment with caffeine occluded phase 2 ([Ca2+]i oscillations) of the action of thyrotropin-releasing hormone (TRH) without modifying phase 1 (Ca2+ release from the intracellular stores). Caffeine also inhibited the [Ca2+]i increase induced by depolarization with high-K+ solutions (56% at 20 mM), suggesting direct inhibition of the Ca2+ entry through voltage-gated Ca2+ channels. We propose that the [Ca2+]i increase induced by caffeine in GH3 cells takes place by a mechanism similar to that of TRH, i.e. membrane depolarization that increases the firing frequency of action potentials. The increase of the electrical activity overcomes the direct inhibitory effect on voltage-gated Ca2+ channels with the result of increased Ca2+ entry and a rise in [Ca2+]i. Consideration of this action cautions interpretation of previous experiments in which caffeine was assumed to increase [Ca2+]i only by facilitating the release of Ca2+ from intracellular Ca2+ stores. 相似文献
7.
Richard H. Kramer Rupa Mokkapatti Edwin S. Levitan 《Pflügers Archiv : European journal of physiology》1994,426(1-2):12-20
Caffeine elicits physiological responses in a variety of cell types by triggering the mobilization of Ca2+ from intracellular organelles. Here we investigate the effects of caffeine on intracellular Ca2+ concentration ([Ca2+]i) and ionic currents in anterior pituitary cells (GH3) cells. Caffeine has a biphasic effect on Ca2+-activated K+ current [I
K(Ca)]: it induces a transient increase superimposed upon a sustained inhibition. While the transient increase coincides with a rise in [Ca2+]i, the sustained inhibition of I
K(Ca) is correlated with a sustained inhibition of the L-type Ca2+ current. The L-type Ca2+ current is also inhibited by other agents that mobilize intracellular Ca2+, including thyrotropin releasing hormone (TRH) and ryanodine, but in a matter distinct from caffeine. Unlike the caffeine effect, the TRH-induced inhibition washes-out under whole-cell patch-clamp conditions and is eliminated by intracellular Ca2+ chelators. Likewise, the ryanodine-induced inhibition desensitizes while the caffeine-induced inhibition does not. Simultaneous [Ca2+]i and Ca2+ current measurements show that caffeine can inhibit Ca2+ current without changing [Ca2+]i. Single-channel recordings show that caffeine reduces mean open time without affecting single-channel conductance of L-type channels. Hence the effects of caffeine on ion channels in GH3 cells are attributable both to mobilization of intracellular Ca2+ and to a direct effect on the gating of L-type Ca2+ channels. 相似文献
8.
Tong Mook Kang Insuk So Ki Whan Kim 《Pflügers Archiv : European journal of physiology》1995,431(1):91-100
In the present experiment, we characterized the intracellular Ca2+ oscillations induced by caffeine (1 mM) or histamine (1–3 M) in voltage-clamped single smooth muscle cells of rabbit cerebral (basilar) artery. Superfusion of caffeine or histamine induced periodic oscillations of large whole-cell K+ current with fairly uniform amplitudes and intervals. The oscillatory K+ current was abolished by inclusion of ethylenebis(oxonitrilo)tetraacetate (EGTA, 5 mM) in the pipette solution. Caffeine- and histamine-induced periodic activation of the large-conductance Ca2+-activated K+ [K(Ca)] channel was recorded in the cell-attached patch mode. These results suggest that the oscillations of K+ current are carried by the K(Ca) channel and reflect the oscillations of intracellular Ca2+ concentration ([Ca2+]i). Ryanodine (1–10 M) abolished both caffeine- and histamine-induced oscillations. Caffeine- induced oscillations were abolished by the sarcoplasmic reticulum Ca2+-adenosine 5-triphosphatase (Ca2+-ATPase) inhibitor, cyclopiazonic acid (10 M), and a high concentration of caffeine (10 mM). Inclusion of heparin (3 mg/ml) in the pipette solution blocked histamine-induced oscillations, but did not block caffeine-induced oscillations. By the removal of extracellular Ca2+, but not by the addition of verapamil and Cd2+, the caffeine-induced oscillations were abolished. Increasing Ca2+ influx rate increased the frequencies of caffeine-induced oscillations. Spontaneous oscillations were also observed in cells that were not superfused with agonists, and had similar characteristics to the caffeine-induced oscillations. From the above results, it is concluded, that in smooth muscle cells of the rabbit cerebral (basilar) artery, ryanodine-sensitive Ca2+-induced Ca2+ release pools play key roles in the generation of caffeine- and histamine-induced intracellular Ca2+ oscillations. 相似文献
9.
Di-8-ANEPPS (4-{2-[6-(dibutylamino)-2-naphthalenyl]-ethenyl}-1-(3-sulfopropyl)pyridinium inner salt) has been used as a fast-response
voltage-sensitive styrylpyridinium probe. However, little is known regarding the mechanism of di-8-ANEPPS actions on ion currents.
In this study, the effects of this dye on ion currents were investigated in pituitary GH3 cells. In whole-cell configuration, di-8-ANEPPS (10 μM) reversibly increased the amplitude of Ca2+-activated K+ current. In inside-out configuration, di-8-ANEPPS (10 μM) applied to the intracellular surface of the membrane caused no
change in single-channel conductance; however, it did enhance the activity of large-conductance Ca2+-activated K+ (BKCa) channels with an EC50 value of 7.5 μM. This compound caused a left shift in the activation curve of BKCa channels with no change in the gating charge of these channels. A decrease in mean closed time of the channels was seen in
the presence of this dye. In the cell-attached mode, di-8-ANEPPS applied on the extracellular side of the membrane also activated
BKCa channels. However, neither voltage-gated K+ nor ether-à-go-go-related gene (erg)-mediated K+ currents in GH3 cells were affected by di-8-APPNES. Under current-clamp configuration, di-8-ANEPPS (10 μM) decreased the firing of action
potentials in GH3 cells. In pancreatic βTC-6 cells, di-8-APPNES (10 μM) also increased BKCa-channel activity. Taken together, this study suggests that during the exposure to di-8-ANEPPS, the stimulatory effects on
BKCa channels could be one of potential mechanisms through which it may affect cell excitability. 相似文献
10.
Daniel G. Lang Aileen K. Ritchie 《Pflügers Archiv : European journal of physiology》1987,410(6):614-622
Single Ca2+-activated K+ channels were studied in membrane patches from the GH3 anterior pituitary cell line. In excised inside-out patches exposed to symmetrical 150 mM KCl, two channel types with conductances in the ranges of 250–300 pS and 9–14 pS were routinely observed. The activity of the large conductance channel is enhanced by internal Ca2+ and by depolarization of the patch membrane. This channel contributes to the repolarization of Ca2+ action potentials but has a Ca2+ sensitivity at –50 mV that is too low for it to contribute to the resting membrane conductance. The small conductance channel is activated by much lower concentrations of Ca2+ at –50 mV, ad its open probability is not strongly voltage sensitive. In cell-attached patches from voltage-clamped cells, the small conductance channels were found to be active during slowly decaying Ca2+-activated K+ tails currents and during Ca2+-activated K+ currents stimulated by thyrotropin-releasing hormone induced elevations of cytosolic calcium. In cell-attached patches on unclamped cells, the small conductance channels were also active at negative membrane potentials when the frequency of spontaneously firing action potentials was high or during the slow afterhyperpolarization following single spontaneous action potentials of slightly prolonged duration. The small conductance channel may thus contribute to the regulation of membrane excitability. 相似文献
11.
C. K. Bauer I. Davison I. Kubasov J. R. Schwarz W. T. Mason 《Pflügers Archiv : European journal of physiology》1994,428(1):17-25
In rat anterior pituitary tumour cells (GH3/B6) thyrotropin-releasing hormone (TRH) elicits a biphasic response. First, a release of intracellularly stored Ca2+ induces a hyperpolarization of the cell. Second, a depolarization thought to be induced by a reduction of the inward-rectifying K+ current (KIR) causes an increase in action potential frequency and a plateau-like increase in [Ca2+]i. It has been proposed that the two phases are induced by the actions of inositol 1,4,5-trisphosphate (InsP
3) and protein kinase C (PKC), respectively, but we demonstrate here that PKC is not responsible for the second phase increase in [Ca2+]i and suggest that the pathways diverge at the level of receptor and G protein coupling. Both phases of the TRH response were insensitive to pertussis toxin, but cholera toxin (CTX) selectively affected the second phase. After CTX pretreatment cells had a high spontaneous spiking frequency and smaller KIR amplitude. In these cells TRH failed to increase the action potential frequency after the first phase hyperpolarization, elicited only a transient peak increase in [Ca2+]i with no plateau phase and could only slightly reduce KIR. These effects of CTX are not mediated by its ability to increase cAMP via activation of GS, as increased cAMP levels neither inhibit KIR nor prevent its reduction by TRH. In addition, inhibition of protein kinase A activation did not block the second phase increase in [Ca2+]i induced by TRH, suggesting that the CTX-sensitive G protein mediating the second phase of the TRH response is not GS.On leave from Uchtomsky-Institute, St. Petersburg University, Russia 相似文献
12.
Mario Díaz Francisco V. Sepúlveda 《Pflügers Archiv : European journal of physiology》1995,430(2):168-180
The whole-cell configuration of the patch-clamp technique was used to examine K+ currents in HeLa cells. Under quasi-physiological ionic gradients, using an intracellular solution containing 10–7 mol/l free Ca2+, mainly outward currents were observed. Large inwardly rectifying currents were elicited in symmetrical 145 mmol/l KCl. Replacement of all extracellular K+ by isomolar Na+, greatly decreased inward currents and shifted the reversal potential as expected for K+ selectivity. The inwardly rectifying K+ currents exhibited little or no apparent voltage dependence within the range of from –120 mV to 120 mV. A square-root relationship between chord conductance and [K+]0 at negative potentials could be established. The inwardly rectifying nature of the currents was unaltered after removal of intracellular Mg2+ and chelation with ATP and ethylenediaminetetraacetic acid (EDTA). Permeability ratios for other monovalent cations relative to K+ were: K+ (1.0)>Rb+ (0.86)>Cs+ (0.12)>Li+ (0.08)>Na+ (0.03). Slope conductance ratios measured at –100 mV were: Rb+ (1.66)>K+ (1.0)>Na+ (0.09)>Li+ (0.08)>Cs+ (0.06). K+ conductance was highly sensitive to intracellular free Ca2+ concentration. The relationship between conductance at 0 mV and Ca2+ concentration was well described by a Hill expression with a dissociation constant, K
D, of 70 nmol/l and a Hill coefficient, n, of 1.81. Extracellular Ba2+ blocked the currents in a concentration- and voltage-dependent manner. The dependence of the K
D for the blockade was analysed using a Woodhull-type treatment, locating the ion interaction site at 19 % of the distance across the electrical field of the membrane and a K
D (0 mV) of 7 mmol/l. Tetraethylammonium and 4-aminopyridine were without effect whilst quinine and quinidine blocked the currents with concentrations for half-maximum effects equal to 7 mol/l and 3.5 mol/l, respectively. The unfractionated venom of the scorpion Leiurus quinquestriatus (LQV) blocked the K+ currents of HeLa cells. The toxins apamin and scyllatoxin had no detectable effect whilst charybdotoxin, a component of LQV, blocked in a voltage-dependent manner with half-maximal concentrations of 40 nmol/l at –120 mV and 189 nmol/l at 60 mV; blockade by charybdotoxin accounts for the effect of LQV. Application of ionomycin (5–10 mol/l), histamine (1 mmol/l) or bradykinin (1–10 mol/l) to cells dialysed with low-buffered intracellular solutions induced K+ currents showing inward rectification and a lack of voltage dependence. 相似文献
13.
Takako Ohno-Shosaku Takahiro Kubota Jun Yamaguchi Masaaki Fukase Takuo Fujita Mamoru Fujimoto 《Pflügers Archiv : European journal of physiology》1989,413(5):562-564
Using the patch clamp technique, we identified an inwardly rectifying K+ channel in the membrane of opossum kidney cells. The single channel conductance was about 90 pS for inward currents and 30 pS for outward currents under a symmetrical high-K+ condition. The activity of the channel was found to decrease with time during recording from inside-out patches. In the solution with submicromolar Ca2+, the activity disappeared within 4–20 min. Intracellular Ca2+ promoted the run-down of the channel activity at 0.1–1 mM, whereas millimolar Mg-ATP restored the activity after run-down. The run-down channels could never be reactivated by ATP in the absence of Mg2+, or by a nonhydrolyzable ATP analog, AMPPNP, even in the presence of Mg2+. 相似文献
14.
Antonio R. Artalejo Antonio G. García Erwin Neher 《Pflügers Archiv : European journal of physiology》1993,423(1-2):97-103
Simultaneous whole-cell patch-clamp and fura-2 fluorescence [Ca2+]i measurements were used to characterize Ca2+-activated K+ currents in cultured bovine chromaffin cells. Extracellular application of histamine (10 M) induced a rise of [Ca2+]i concomitantly with an outward current at holding potentials positive to –80 mV. The activation of the current reflected an increase in conductance, which did not depend on membrane potential in the range –80 mV to –40 mV. Increasing the extracellular K+ concentration to 20 mM at the holding potential of –78 mV was associated with inwardly directed currents during the [Ca2+]i elevations induced either by histamine (10 M) or short voltage-clamp depolarizations. The current reversal potential was close to the K+ equilibrium potential, being a function of external K+ concentration. Current fluctuation analysis suggested a unit conductance of 3–5 pS for the channel that underlies this K+ current. The current could be blocked by apamin (1 M). Whole-cell current-clamp recordings snowed that histamine (10 M) application caused a transient hyperpolarization, which evolved in parallel with the [Ca2+]i changes. It is proposed that a small-conductance Ca2+-activated K+ channel is present in the membrane of bovine chromaffin cells and may be involved in regulating catecholamine secretion by the adrenal glands of various species. 相似文献
15.
Liang GH Kim MY Park S Kim JA Choi S Suh SH 《Pflügers Archiv : European journal of physiology》2008,457(1):67-75
We studied the effects of Na+ influx on large-conductance Ca2+-activated K+ (BKCa) channels in cultured human umbilical vein endothelial cells (HUVECs) by means of patch clamp and SBFI microfluorescence
measurements. In current-clamped HUVECs, extracellular Na+ replacement by NMDG+ or mannitol hyperpolarized cells. In voltage-clamped HUVECs, changing membrane potential from 0 mV to negative potentials
increased intracellular Na+ concentration ([Na+]i) and vice versa. In addition, extracellular Na+ depletion decreased [Na+]i. In voltage-clamped cells, BKCa currents were markedly increased by extracellular Na+ depletion. In inside-out patches, increasing [Na+]i from 0 to 20 or 40 mM reduced single channel conductance but not open probability (NPo) of BKCa channels and decreasing intracellular K+ concentration ([K+]i) gradually from 140 to 70 mM reduced both single channel conductance and NPo. Furthermore, increasing [Na+]i gradually from 0 to 70 mM, by replacing K+, markedly reduced single channel conductance and NPo. The Na+–Ca2+ exchange blocker Ni2+ or KB-R7943 decreased [Na+]i and increased BKCa currents simultaneously, and the Na+ ionophore monensin completely inhibited BKCa currents. BKCa currents were significantly augmented by increasing extracellular K+ concentration ([K+]o) from 6 to 12 mM and significantly reduced by decreasing [K+]o from 12 or 6 to 0 mM or applying the Na+–K+ pump inhibitor ouabain. These results suggest that intracellular Na+ inhibit single channel conductance of BKCa channels and that intracellular K+ increases single channel conductance and NPo.
GH Liang and MY Kim contributed equally to this publication and therefore share the first authorship. 相似文献
16.
[Ca2+]i-dependent membrane currents in guinea-pig ventricular cells in the absence of Na/Ca exchange
Karin R. Sipido Geert Callewaert Francesco Porciatti Johan Vereecke Edward Carmeliet 《Pflügers Archiv : European journal of physiology》1995,430(5):871-878
Transient inward currents (I
ti) during oscillations of intracellular [Ca2+] ([Ca2+]i) in ventricular myocytes have been ascribed to Na/Ca exchange. We have investigated whether other Ca2+-dependent membrane currents contribute to I
ti in single guinea-pig ventricular myocytes, by examining membrane currents during [Ca2+]i oscillations and during caffeine-induced Ca2+ release from the sarcoplasmic reticulum in the absence of Na+. Membrane currents were recorded during whole-cell voltage clamp and [Ca2+]i measured simultaneously with fura-2. In the absence of Na/Ca exchange, i.e., with Li+, Cs+ or N-methyl-D-glucamine (NMDG+) substituted for Na+, the cell could be loaded with Ca2+ by repetitive depolarizations to +10 mV, resulting in spontaneous [Ca2+]i oscillations. During these oscillations, no inward currents were seen, but instead spontaneous Ca2+ release was accompanied by a shift of the membrane current in the outward direction at potentials between –40 mV and +60 mV. This [Ca2+]i-dependent outward current shift was not abolished when NMDG+ was substituted for internal monovalent cations, nor was it sensitive to substitution of external Cl–. It was however, sensitive to the blockade of ICa by verapamil. These results suggest that the transient outward current shift observed during spontaneous Ca2+ release represents [Ca2+]idependent transient inhibition of I
Ca. Similarly, during the [Ca2+]i transients induced by brief caffeine (10 mM) applications, we could not detect membrane currents attributable to a Ca2+-activated nonselective cation channel, or to a Ca2+-activated Cl– channel; however, transient Ca2+-dependent inhibition of I
Ca was again observed. We conclude that neither the Ca2+-activated nonselective cation channel nor the Ca2+-activated Cl– channel contribute significantly to the membrane currents during spontaneous [Ca2+]i oscillations in guineapig ventricular myocytes. However, in the voltage range between –40 mV and +60 mV Ca2+-dependent transient inhibition of I
Ca will contribute to the oscillations of the membrane current. 相似文献
17.
Kyu-Sang Park Seung-Kuy Cha Min-Jeong Kim Na-Hyun Kim Joong-Woo Lee Seong-Woo Jeong In Deok Kong 《Neuroscience letters》2010
The electrophysiological mechanism underlying afterhyperpolarization induced by the activation of the nicotinic acetylcholine receptor (nAChR) in male rat major pelvic ganglion neurons (MPG) was investigated using a gramicidin-perforated patch clamp and microscopic fluorescence measurement system. Acetylcholine (ACh) induced fast depolarization through the activation of nAChR, followed by a sustained hyperpolarization after the removal of ACh in a dose-dependent manner (10 μM to 1 mM). ACh increased both intracellular Ca2+ ([Ca2+]i) and Na+ concentrations ([Na+]i) in MPG neurons. The recovery of [Na+]i after the removal of ACh was markedly delayed by ouabain (100 μM), an inhibitor of Na+/K+ ATPase. Pretreatment with ouabain blocked ACh-induced hyperpolarization by 67.2 ± 5.4% (n = 7). ACh-induced hyperpolarization was partially attenuated by either the chelation of [Ca2+]i with BAPTA/AM (20 μM) or the blockade of small-conductance Ca2+-activated K+ channels by apamin (500 nM). Taken together, the activation of nAChR increases [Na+]i and [Ca2+]i, which activates Na+/K+ ATPase and Ca2+-activated K+ channels, respectively. Consequently, hyperpolarization occurs after the activation of nAChR in the autonomic pelvic ganglia. 相似文献
18.
Park JK Kim YC Sim JH Choi MY Choi W Hwang KK Cho MC Kim KW Lim SW Lee SJ 《Pflügers Archiv : European journal of physiology》2007,454(2):307-319
Employing microfluorometric system and patch clamp technique in rabbit basilar arterial myocytes, regulation mechanisms of
vascular excitability were investigated by applying intracellular pH (pHi) changers such as sodium acetate (SA) and NH4Cl. Applications of caffeine produced transient phasic contractions in a reversible manner. These caffeine-induced contractions
were significantly enhanced by SA and suppressed by NH4Cl. Intracellular Ca2+ concentration ([Ca2+]i) was monitored in a single isolated myocyte and based the ratio of fluorescence using Fura-2 AM (R
340/380). SA (20 mM) increased and NH4Cl (20 mM) decreased R
340/380 by 0.2 ± 0.03 and 0.1 ± 0.02, respectively, in a reversible manner. Caffeine (10 mM) transiently increased R
340/380 by 0.9 ± 0.07, and the ratio increment was significantly enhanced by SA and suppressed by NH4Cl, implying that SA and NH4Cl may affect [Ca2+]i (p < 0.05). Accordingly, we studied the effects of SA and NH4Cl on Ca2+-activated K+ current (IKCa) under patch clamp technique. Caffeine produced transient outward current at holding potential (V
h) of 0 mV, caffeine induced transient outward K+ current, and the spontaneous transient outward currents were significantly enhanced by SA and suppressed by NH4Cl. In addition, IKCa was significantly increased by acidotic condition when pHi was lowered by altering the NH4Cl gradient across the cell membrane. Finally, the effects of SA and NH4Cl on the membrane excitability and basal tension were studied: Under current clamp mode, resting membrane potential (RMP)
was −28 ± 2.3 mV in a single cell level and was depolarized by 13 ± 2.4 mV with 2 mM tetraethylammonium (TEA). SA hyperpolarized
and NH4Cl depolarized RMP by 10 ± 1.9 and 16 ± 4.7 mV, respectively. SA-induced hyperpolarization and relaxation of basal tension
was significantly inhibited by TEA. These results suggest that SA and NH4Cl might regulate vascular tone by altering membrane excitability through modulation of [Ca2+]i and Ca2+-activated K channels in rabbit basilar artery. 相似文献
19.
Stephen M. Sims Melanie E. M. Kelly S. Jeffrey Dixon 《Pflügers Archiv : European journal of physiology》1991,419(3-4):358-370
Membrane electrical properties of freshly isolated rat osteoclasts were studied using patch-clamp recording methods. Characterization of the passive membrane properties indicated that the osteoclast cell membrane behaved as an isopotential surface. The specific membrane capacitance was 1.2±0.3 F/cm2 (mean ±SD), with no difference between cells plated on glass and those adhering to a permeable collagen substrate. The current/voltage (I/V) relationship of all cells showed inward rectification and I/V curves shifted 51 mV positive per tenfold increase of [K+]out, indicating an inwardly rectifying K+ conductance. The voltage dependence of the K+ chord conductance (g
K) also shifted positive along the voltage axis, and the maximum conductance increased, with elevation of [K+]out. g
K for cells bathed in 4.7 mM [K+]out increased e-fold per 12mV hyperpolarization, and half-maximal activation was at –89 mV. Approximately 18% (50 pS/pF) of the maximum g
K was active at –70 mV. Inward single-channel currents were recorded in cell-attached patches at hyperpolarizing potentials. With symmetrical K+, channel conductance was 25±3 pS and reversal was close to the K+ equilibrium potential, consistent with this K+ channel underlying the whole-cell K+ currents. With both conventional whole-cell and perforated-patch recording, no voltage-activated Ca2+ current was detected. In approximately 30% of osteoclasts studied, an outwardly rectifying current was observed, which was reversibly blocked by 4,4-diisothiocyanostilbene-2,2-disulphonic acid (DIDS) and 4-acetamido-4-isothiocyanostilbene2,2-disulphonic acid (SITS). This DIDS- and SITS-sensitive current reversed direction at the chloride equilibrium potential. We conclude that an inwardly rectifying K+ current is present in all rat osteoclasts and that some osteoclasts also exhibit an outwardly rectifying Cl– current. Both these membrane conductances may play an important physiological role by dissipating the potential that arises from the electrogenic transport of H+ across the ruffled membrane of the osteoclast. 相似文献
20.
Carlos Villalobos Javier García-Sancho 《Pflügers Archiv : European journal of physiology》1995,430(6):923-935
Treatment of GH3 cells with either hypothalamic peptide thyrotropin-releasing hormone (TRH), the endomembrane Ca2+-ATPase inhibitor thapsigargin or the Ca2+ ionophore ionomycin mobilized, with different kinetics, essentially all of the Ca2+ pool from the intracellular Ca2+ stores. Any of the above-described treatments induced a sustained increase in intracellular Ca2+ concentration ([Ca2+]i), which was dependent on extracellular Ca2+ and was prevented by Ni2+ but not by dihydropyridines (DHPs), suggesting that it was due to capacitative Ca2+ entry via activation of a plasma membrane pathway which opened upon the emptying of the intracellular Ca2+ stores. The increase of the plasma membrane permeability to Ca2+ correlated negatively with the filling degree of the intracellular Ca2+ stores and was reversed by refilling of the stores. The mechanism of capacitative Ca2+ entry into GH3 cells differed from similar mechanisms described in several types of blood cells in that the pathway was poorly permeable to Mn2+ and not sensitive to cytochrome P450 inhibitors. In GH3 cells, TRH induced a transient [Ca2+]i increase due to Ca2+ release from the stores (phase 1) followed by a sustained [Ca2+]i increase due to Ca2+ entry (phase 2). At the single-cell level, phase 2 was composed of a DHP-insensitive sustained [Ca2+]i increase, due to activation of capacitative Ca2+ entry, superimposed upon which DHP-sensitive [Ca2+]i oscillations took place. The two components of the TRH-induced Ca2+ entry differed also in that [Ca2+]i oscillations remained for several minutes after TRH removal, whereas the sustained [Ca2+]i increase dropped quickly to prestimulatory levels, following the same time course as the refilling of the stores. The drop was prevented when the refilling was inhibited by thapsigargin. It is concluded that, even though the mechanisms of capacitative Ca2+ entry may show differences from cell to cell, it is also present and may contribute to the regulation of physiological functions in excitable cells such as GH3. There, capacitative Ca2+ entry cooperates with voltage-gated Ca2+ channels to generate the [Ca2+]i increase seen during phase 2 of TRH action. This contribution of capacitative Ca2+ entry may be relevant to the enhancement of prolactin secretion induced by TRH. 相似文献