共查询到20条相似文献,搜索用时 15 毫秒
1.
W. Schaefer J. Beeker F. A. Gries 《Journal of molecular medicine (Berlin, Germany)》1988,66(10):443-446
Summary The influence of hyperglycemia on calmodulin-stimulated Ca2+-Mg2+-ATPase activity was studied in 20 diabetic subjects. A clear inverse relationship between short-term hyperglycemia as well as chronic hyperglycemia and calmodulin-stimulated Ca2+-Mg2+-ATPase activity could be demonstrated. Such a relationship could not be shown for basal enzyme activity.Abbreviations ATPase
Adenosine 5-triphosphatase
- Pi
Inorganic phosphate
- TBA
2-Thiobarbituric acid
This work was supported by the Bundesminister für Jugend, Frauen, Familie und Gesundheit, Bonn, and the Minister für Wissenschaft und Forschung des Landes Nordrhein-Westfalen, Düsseldorf, Federal Republic of GermanySome results are part of the thesis of J. Beeker 相似文献
2.
目的: 构建磷酸受纳蛋白(PLB)反义RNA腺相关病毒载体(rAAV-asPLB),建立糖尿病(DM)大鼠模型。直接心肌注射rAAV-asPLB,观察其对DM大鼠心肌PLB基因转录和蛋白表达的影响,以及对心肌肌浆网Ca2+-ATPase活性的作用。方法: 利用质粒辅助重组腺相关病毒系统试剂盒构建rAAV-asPLB。腹腔注射链脲佐菌素(STZ)诱导DM大鼠模型,将实验动物分为4组:正常组、DM组、盐水组和rAAV-asPLB组。盐水或rAAV-asPLB注射后6周,RT-PCR检测心肌PLB mRNA转录;Western blotting检测PLB蛋白表达水平;检测心肌肌浆网Ca2+-ATPase活性。结果: (1)成功构建rAAV-asPLB,诱导出DM大鼠模型。(2)DM组和盐水组PLB mRNA水平均高于正常组;rAAV-asPLB组PLB mRNA水平较DM组和盐水组明显降低。 (3)DM组和盐水组PLB 蛋白水平均高于正常组;rAAV-asPLB组PLB 蛋白水平较DM组和盐水组明显降低。(4)肌浆网Ca2+-ATPase活性在DM组和盐水组中较正常组明显降低,而rAAV-asPLB组较DM组和盐水组升高。结论: rAAV-asPLB抑制DM大鼠心肌PLB表达,增强Ca2+-ATPase活性。 相似文献
3.
L. Missiaen F. X. Lemaire J. B. Parys H. De Smedt I. Sienaert R. Casteels 《Pflügers Archiv : European journal of physiology》1996,431(3):318-324
Intracellular Ca2+ signals in response to inositol 1,4,5-trisphosphate-producing agents often present themselves as Ca2+ oscillations and propagating Ca2+ waves originating at discrete initiation sites. We studied the spatial organization of the Ca2+ signal in single CPAE endothelial cells stimulated with adenosine triphosphate. The long, thin processes presented a higher agonist sensitivity and, for the same agonist concentration, a faster rise in cytoplasmic Ca2+ concentration and rate of wave propagation than the cell body. Ca2+ waves originated preferentially in one of these processes and then invaded the cell body. Removal of external Ca2+ induced a progressive inhibition up to blockade of the response in the process but not in the cell body. These findings suggest that CPAE cells contain many individual store units, each of which has the inherent ability to set the stage for Ca2+ release. A diffusing messenger originating from the initiation zone then coordinates the events leading to Ca2+ release in the individual store units to produce a Ca2+ wave. 相似文献
4.
The leading role of membrane Ca(2+)-ATPase in recovery of Ca(2+) homeostasis after glutamate shock 总被引:3,自引:0,他引:3
Storozhevykh TP Pinelis VG Vinskaya NP Surin AM Khodorov BI 《Bulletin of experimental biology and medicine》2003,135(2):139-142
Combined blockade of Na+/Ca2+ exchange, Ca2+ uptake by mitochondria and endoplasmic reticulum usually does not prevent recovery of the basal level of intracellular Ca2+ after 1-min action of glutamate (100 M) or K+ (50 mM). However, replacement of Ca2+ with Ba2+, which cannot be transported by Ca2+-ATPase, considerably delayed the decrease in intracellular Ba2+ after its rise caused by glutamate or potassium application in all examined cells, which attest to an important role of Ca2+-ATPase in Ca2+ extrusion after the action of glutamate or K+. 相似文献
5.
Ca2+-activated maxi K+ channels were studied in inside-out patches from smooth muscle cells isolated from either porcine coronary arteries or guinea-pig urinary bladder. As described by Groschner et al. (Pflügers Arch 417:517, 1990), channel activity (NP
o) was stimulated by 3 M [Ca2+]c (1 mM Ca-EGTA adjusted to a calculated pCa of 5.5) and was suppressed by the addition of 1 mM Na2ATP. The following results suggest that suppression of NP
o by Na2ATP is due to Ca2+ chelation and hence reduction of [Ca2+]c and reduced Ca2+ activation of the channel. The effect was absent when Mg ATP was used instead of Na2ATP. The effect was diminished by increasing the [EGTA] from 1 to 10 mM. The effect was absent when [Ca2+]c was buffered with 10 mM HDTA (apparent pK
Ca 5.58) instead of EGTA (pK
Ca 6.8). A Ca2+-sensitive electrode system indicated that 1 mM Na2ATP reduced [Ca2+]c in 1 mM Ca-EGTA from 3 M to 1.4 M. Na2ATP, Na2GTP, Li4AMP-PNP and NaADP reduced measured [Ca2+]c in parallel with their suppression of NP
o. After the Na2ATP-induced reduction of [Ca2+]c was re-adjusted by adding either CaCl2 or MgCl2, the effect of Na2ATP on NP
o disappeared. In vivo, intracellular [Mg2+] exceeds free [ATP4–], hence ATP modulation of maxi K+ channels due to Ca2+ chelation is without biological relevance. 相似文献
6.
PURPOSE: The sarco/endoplasmic reticulum Ca2+-ATPase (SERCA), encoded by ATP2A2, is an essential component for G-protein coupled receptor (GPCR)-dependent Ca2+ signaling. However, whether the changes in Ca2+ signaling and Ca2+ signaling proteins in parotid acinar cells are affected by a partial loss of SERCA2 are not known. MATERIALS AND METHODS: In SERCA2+/- mouse parotid gland acinar cells, Ca2+ signaling, expression levels of Ca2+ signaling proteins, and amylase secretion were investigated. RESULTS: SERCA2+/- mice showed decreased SERCA2 expression and an upregulation of the plasma membrane Ca2+ ATPase. A partial loss of SERCA2 changed the expression level of 1, 4, 5-tris-inositolphosphate receptors (IP3Rs), but the localization and activities of IP3Rs were not altered. In SERCA2+/- mice, muscarinic stimulation resulted in greater amylase release, and the expression of synaptotagmin was increased compared to wild type mice. CONCLUSION: These results suggest that a partial loss of SERCA2 affects the expression and activity of Ca2+ signaling proteins in the parotid gland acini, however, overall Ca2+ signaling is unchanged. 相似文献
7.
Mayte Montero Sara R. Alonso-Torre Javier Alvarez Ana Sanchez Javier García-Sancho 《Pflügers Archiv : European journal of physiology》1993,424(5-6):465-469
The pathway for refilling the intracellular Ca2+ stores of HL60 and U937 human leukaemia cells loaded with fura-2 has been investigated. On addition of external Ca2+ to cells with empty stores there was an increase in the cytosolic Ca2+ concentration ([Ca2+]i) which preceded the refilling of the stores. The increase in [Ca2+]i was faster than the refilling, by 3-to 15-fold, depending on the cell type. In measurements in single HL60 cells we found that the refilling of the stores correlated with the extent of the [Ca2+]i increase on addition of external Ca2+. The cells showing no [Ca2+]i increase were unable to refill their stores. The addition of Ni2+ to the extracellular medium prevented both the [Ca2+]i increase and the refilling of the stores. These results indicate that the limiting step for store refilling is the entry of Ca2+ from the extracellular medium to the cytosol. Hence, we conclude that extracellular Ca2+ cannot gain access directly to the intracellular Ca2+ stores in these cells, but must first enter the cytosol and be taken up from there into the stores. 相似文献
8.
Ad A. G. M. Benders Jie Li Robert A. C. Lock René J. M. Bindels Sjoerd E. Wendelaar Bonga Jacques H. Veerkamp 《Pflügers Archiv : European journal of physiology》1994,428(5-6):461-467
Copper (Cu2+) intoxication has been shown to induce pathological changes in various tissues. The mechanism underlying Cu2+ toxicity is still unclear. It has been suggested that the Na+/K+-ATPase and/or a change of the membrane permeability may be involved. In this study we examined the effects of Cu2+ on the Na+ and Ca2+ homeostasis of cultured human skeletal muscle cells using the ion-selective fluorescent probes Na+-binding benzofuran isophtalate (SBFI) and Fura-2, respectively. In addition, we measured the effect of Cu2+ on the Na+/K+-ATPase activity. Cu2+ and ouabain increase the cytoplasmic free Na+ concentration ([Na+]i). Subsequent addition of Cu2+ after ouabain does not affect the rate of [Na+]i increase. Cu2+ inhibits the Na+/K+-ATPase activity with an IC50 of 51 M. The cytoplasmic free Ca2+ concentration ([Ca2+]i) remains unaffected for more than 10 min after the administration of Cu2+. Thereafter, [Ca2+]i increases as a result of the Na+/Ca2+-exchanger operating in the reversed mode. The effects of Cu2+ on the Na+ homeostasis are reversed by the reducing and chelating agent dithiothreitol and the heavy metal chelator N,N,N,N,-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN). In conclusion, SBFI is a good tool to examine Na+ homeostasis in cultured human skeletal muscle cells. Under the experimental conditions used, Cu2+ does not modify the general membrane permeability, but inhibits the Na+/K+-pump leading to an increase of [Na+]i. As a consequence the operation mode of the Na+/Ca2+-exchanger reverses and [Ca2+]i rises.The authors thank staff and coworkers of the Department of Neurology of the University Hospital Nijmegen, Nijmegen for their kind cooperation in obtaining muscle biopsies. Mr. Arie Oosterhof is gratefully acknowledged for culturing of the human muscle cells. The Prinses Beatrix Fonds and the Dutch-Chinese scientific exchange program contributed financial support for this study. 相似文献
9.
10.
Several studies have already established that the stimulation of H1 receptors by exogenous histamine induces intracellular Ca2+ oscillations in HeLa cells. The molecular mechanism underlying this oscillatory process remains, however, unclear. A series of fura-2 experiments was undertaken in which the nature of the Ca2+ pools involved in the histamine-induced Ca2+ oscillations was investigated using the tumour promoter agent thapsigargin (TG) and the Ca2+-induced Ca2+-release promoter, caffeine. The results obtained indicate first that TG causes a gradual increase in cytosolic Ca2+ without inducing internal Ca2+ oscillations, and second that TG and histamine share common internal Ca2+ storage sites. The latter conclusion was derived from experiments performed in the absence of external Ca2+, where the addition of TG before histamine resulted in a total inhibition of the Ca2+ response linked to H1 receptor stimulation, whereas the addition of histamine before TG decreased by more than 90% the TG-induced Ca2+ release. Finally, TG was found to inhibit irreversibly histamine-induced Ca2+ oscillations when added to the bathing medium during the oscillatory process. The effect of caffeine at concentrations ranging from 1 mM to 10 mM on intracellular Ca2+ homeostasis was also investigated. The results obtained show that caffeine does not affect systematically the internal Ca2+ concentration in resting and TG-stimulated HeLa cells, but increases the Ca2+ sequestration ability of inositol-trisphosphate (InsP
3)-related Ca2+ stores. These results suggest either that TG acts on InsP
3-sensitive as well as InsP
3-insensitive Ca2+ pools, so that no final conclusion on the nature of the pools involved in Ca2+ spike generation can be currently drawn, or that the contribution of an InsP
3-insensitive Ca2+-induced Ca2+-release process is not essential to the Ca2+ oscillation machinery in these cells. It is also concluded that a release of Ca2+ by caffeine may not be directly accessible to fura-2 measurements in this cellular preparation, but that the inhibitory effect of caffeine on the Ca2+ mobilization process triggered by InsP
3 can be clearly documented using this experimental approach. 相似文献
11.
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
12.
R. Nitschke J. Leipziger R. Greger 《Pflügers Archiv : European journal of physiology》1993,423(5-6):519-526
In the present study we have investigated the mechanism of intracellular Ca2+ activity ([Ca2+]i) changes in HT29 cells induced by adenosine triphosphate (ATP), carbachol (CCH), and neurotensin (NT). [Ca2+]i was measured with the fluorescent Ca2+ indicator fura-2 at the single-cell level or in small cell plaques with high time resolution (1–40Hz). ATP and CCH induced not only a dose-dependent [Ca2+]i peak response, but also changes of the plateau phase. The [Ca2+]i plateau was inversely dependent on the ATP concentration, whereas the CCH-induced [Ca2+]i plateau increased at higher CCH concentrations. NT showed (from 10–10 to 10–7 mol/l) in most cases only a [Ca2+]i spike lasting 2–3 min. The [Ca2+]i plateau induced by ATP (10–6 mol/l) and CCH (10–5 mol/l) was abolished by reducing the Ca2+ activity in the bath from 10–3 to 10–4 mol/l (n=7). In Ca2+-free bathing solution the [Ca2+]i peak value for all three agonists was not altered. Using fura-2 quenching by Mn2+ as an indicator of Ca2+ influx the [Ca2+]i peak was always reached before Mn2+ influx started. Every agonist showed this delayed stimulation of the Ca2+ influx with a lag time of 23±1.5 s (n=15) indicating a similar mechanism in each case. Verapamil (10–6–10–4 mol/l) blocked dose dependently both phases (peak and plateau) of the CCH-induced [Ca2+]i increase. Short pre-incubation with verapamil augmented the effect on the [Ca2+]i peak, whereas no further influence on the plateau was observed. Ni2+ (10–3 mol/l) reduced the plateau value by 70%. 相似文献
13.
B. Himpens L. Missiaen G. Droogmans R. Casteels 《Pflügers Archiv : European journal of physiology》1991,417(6):645-650
The effects of different compounds that inhibit the isolated plasma-membrane Ca2+/Mg2+-ATPase on the cytosolic free Ca2+ concentration ([Ca2+]i) and on the corresponding force development have been examined in smooth muscle of the longitudinal layer of the guinea-pig ileum. F–, in the presence of Al3+, induced an increase of the resting force and of the amplitude of the superimposed phasic contractions. The increase of resting force was associated with an increased level of basal [Ca2+]i while the phasic contractions were accompanied by concomitant oscillations in [Ca2+]i. Comparable contractions could be induced by vanadate and the calmodulin antagonist calmidazolium. The oscillations of [Ca2+]i and of force elicited by AlF
4
–
were not modified by adrenergic or cholinergic blocking agents but were inhibited by verapamil. These phasic contractions were not affected by depleting the intracellular Ca2+ stores with ryanodine. This finding excludes a cytosolic origin of these oscillations. However, hyperpolarization and complete depolarization of the cells inhibited the oscillations. It is concluded that AlF
4
–
, vanadate and calmidazolium induce cytoplasmic Ca2+ oscillations possibly by acting at the plasma membrane. Indeed all these substances affect by different mechanisms the isolated plasma-membrane Ca2+/Mg2+-ATPase. The generation of membrane-linked Ca2+ oscillations could therefore be related to an inhibition of the plasma-membrane Ca2+ pump resulting in an increase of [Ca2+]i. This change in [Ca2+]i could be responsible for the pronounced changes of the electrical and mechanical activity of this tissue. 相似文献
14.
Ca2+ release from the sarcoplasmic reticulum (SR) of mammalian cardiac myocytes occuring either due to activation by a depolarization or the resulting transmembrane Ca2+ current (I
Ca), or spontaneously due to Ca2+ overload has been shown to cause inward current(s) at negative membrane potentials. In this study, the effects of different intracellular Ca2+ chelating compounds on I
Ca-evoked or spontaneous Ca2+-release-dependent inward currents were examined in dialysed atrial myocytes from hearts of adult guinea-pigs by means of whole-cell voltage-clamp. As compared to dialysis with solutions containing only a low concentration of a high affinity ethylene glycol-bis(-aminoethylether) N,N,N,N-tetraacetic acid (EGTA) like chelator (50–200 M), inward membrane currents (at –50 mV) due to evoked Ca2+ release, spontaneous Ca2+ release or Ca2+ overload following long-lasting depolarizations to very positive membrane potentials are prolonged if the dialysing fluid contains a high concentration of a low affinity Ca2+ chelating compound such as citrate or free adenosine 5-triphosphate (ATP). Without such a non-saturable Ca2+ chelator in the dialysing fluid, Ca2+-release-dependent inward currents are often oscillatory and show an irregular amplitude. With a low affinity chelator in a non-saturable concentration, discrete inward currents with constant properties can be recorded. We conclude that the variability in Ca2+-release-dependent inward current seen in single cells arises from spatial inhomogeneities of intracellular Ca2+ concentration ([Ca2+]i) due to localized saturation of endogenous and exogenous high affinity Ca2+ buffers (e.g. [2]). This can be avoided experimentally by addition of a non-saturable buffer to the intracellular solution. This condition might be useful, if properties of Ca2+ release from the SR and/ or the resulting membrane current, like for example arrhythmogenic transient inward current, are to be investigated on the single cell level. 相似文献
15.
Annegret Herrmann-Frank Edward Darling Gerhard Meissner 《Pflügers Archiv : European journal of physiology》1991,418(4):353-359
The Ca2+-gated Ca2+ release channel of aortic sarcoplasmic reticulum (SR) was partially purified and reconstituted into planar lipid bilayers. Canine and porcine aorta microsomal protein fractions were solubilized in the detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulphonate (CHAPS) in the presence and absence of 3[H]-ryanodine and centrifuged through linear sucrose gradients. A single 3[H]-ryanodine receptor peak with an apparent sedimentation coefficient of 30 s was obtained. Upon reconstitution into planar lipid bilayers, the unlabelled 30 s protein fraction induced the formation of a Ca2+- and monovalent-ion-conducting channel (110 pS in 100 mM Ca2+, 360 pS in 250 mM K+). The channel was activated by micromolar Ca2+, modulated by millimolar adenosine triphosphate, Mg2+ and the Ca2+-releasing drug caffeine, and inhibited by micromolar ruthenium red. Micro- to millimolar concentrations of the plant alkaloid ryanodine induced a permanently closed state of the channel. Our results suggest that smooth muscle SR contains a Ca2+-gated Ca2+ release pathway, with properties similar to those observed for the skeletal and cardiac ryanodine receptor/Ca2+ release channel complexes. 相似文献
16.
Leszek Wojnowski Albrecht Schwab John Hoyland William T. Mason Stefan Silbernagl Hans Oberleithner 《Pflügers Archiv : European journal of physiology》1994,426(1-2):95-100
Transformed Mardin-Darby canine kidney-focus (MDCK-F) cells exhibit spontaneous Ca2+ oscillations from an inositol 1,4,5-trisphosphate-sensitive cytoplasmic Ca2+ store. In this study, Ca2+ entry from the extracellular space and its role in generation of oscillations were investigated by means of Ca2+ video imaging and the Fura-2/Mn2+ quenching technique. Oscillations were dependent on extracellular Ca2+ concentration and were inhibited by extracellularly applied La3+, Co2+ and Ni2+. Depolarization of the cell membrane with high K+ concentrations and the L-type Ca2+ channel blocker nifedipine had no effect on oscillations, indicating the lack of involvement of voltage-gated Ca2+ channels. Mn2+ quenching experiments disclosed significant Ca2+ influx into MDCK-F cells. The rate of this influx was constant between Ca2+ spikes, but markedly increased during the spontaneous Ca2+ spikes. Similar transient increases in Ca2+ entry could be mimicked by agents triggering intracellular Ca2+ release such as bradykinin and thapsigargin. We conclude that the plasma membrane of MDCK-F cells exhibits a marked voltage-independent Ca2+ permeability permitting Ca2+ entry into the cytoplasm. The rate of Ca2+ entry which determines the frequency of oscillations is most likely to be regulated by the cytoplasmic Ca2+ concentration. 相似文献
17.
N. P. Aimasheva E. B. Malenyuk E. B. Manukhina G. L. Khaspekov V. D. Mikoyan L. N. Kubrina A. F. Vanin I. Yu. Malyshev 《Bulletin of experimental biology and medicine》1999,128(4):981-984
This study verifies the hypothesis that NO-dependent regulation of sarcoplasmic reticulum Ca2+-ATPase gene (SERCA) plays an important role in preventing Ca2+ overload after exposure to damaging factors. The data confirmed NO-dependent activation of SERCA expression and important
role of this mechanism in the reduction of calcium overload.
Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol 128, No. 10, pp. 375–379, October, 1999 相似文献
18.
Meuth SG Kanyshkova T Landgraf P Pape HC Budde T 《Pflügers Archiv : European journal of physiology》2005,450(2):111-122
Ca2+-dependent inactivation (CDI) of high-voltage activated (HVA) Ca2+ channels was investigated in acutely isolated and identified thalamocortical relay neurons of the dorsal lateral geniculate nucleus (dLGN) by combining electrophysiological and immunological techniques. The influence of Ca2+-binding proteins, calmodulin and the cytoskeleton on CDI was monitored using double-pulse protocols (a constant post-pulse applied shortly after the end of conditioning pre-pulses of increasing magnitude). Under control conditions the degree of inactivation (34±9%) revealed a U-shaped and a sigmoid dependency of the post-pulse current amplitude on pre-pulse voltage and charge influx, respectively. In contrast to a high concentration (5.5 mM) of EGTA (31±3%), a low concentration (3 µM) of parvalbumin (20±2%) and calbindinD28K (24±4%) significantly reduced CDI. Subtype-specific Ca2+ channel blockers indicated that L-type, but not N-type Ca2+ channels are governed by CDI and modulated by Ca2+-binding proteins. These results point to the possibility that activity-dependent changes in the intracellular Ca2+-binding capacity can influence CDI substantially. Furthermore, calmodulin antagonists (phenoxybenzamine, 22±2%; calmodulin binding domain, 17±1%) and cytoskeleton stabilizers (taxol, 23±5%; phalloidin, 15±3%) reduced CDI. Taken together, these findings indicate the concurrent occurrence of different CDI mechanisms in a specific neuronal cell type, thereby supporting an integrated model of this feedback mechanism and adding further to the elucidation of the role of HVA Ca2+ channels in thalamic physiology. 相似文献
19.
Propagation of odor-induced Ca(2+) transients from the cilia/knob to the soma in mammalian olfactory receptor neurons (ORNs) is thought to be mediated exclusively by high-voltage-activated Ca(2+) channels. However, using confocal Ca(2+) imaging and immunocytochemistry we identified functional T-type Ca(2+) channels in rat ORNs. Here we show that T-type Ca(2+) channels in ORNs also mediate propagation of odor-induced Ca(2+) transients from the knob to the soma. In the presence of the selective inhibitor of T-type Ca(2+) channels mibefradil (10-15 microM) or Ni(2+) (100 microM), odor- and forskolin/3-isobutyl-1-methyl-xanthine (IBMX)-induced Ca(2+) transients in the soma and dendrite were either strongly inhibited or abolished. The percentage of inhibition of the Ca(2+) transients in the knob, however, was 40-50% less than that in the soma. Ca(2+) transients induced by 30 mM K(+) were partially inhibited by mibefradil, but without a significant difference in the extent of inhibition between the knob and soma. Furthermore, an increase of as little as 2.5 mM in the extracellular K(+) concentration (7.5 mM K(+)) was found to induce Ca(2+) transients in ORNs, and such responses were completely inhibited by mibefradil or Ni(2+). Total replacement of extracellular Na(+) with N-methyl-d-glutamate inhibited none of the odor-, forskolin/IBMX- or 7.5 mM K(+)-induced Ca(2+) transients. Positive immunoreactivity to the Ca(v)3.1, Ca(v)3.2 and Ca(v)3.3 subunits of the T-type Ca(2+) channel was observed throughout the soma, dendrite and knob. These data suggest that involvement of T-type Ca(2+) channels in the propagation of odor-induced Ca(2+) transients in ORNs may contribute to signal transduction and odor sensitivity. 相似文献
20.
Gervaise Loirand Pierre Pacaud 《Pflügers Archiv : European journal of physiology》1995,430(3):429-436
Effects of exogenous adenosine 5-triphosphate (ATP) were studied by measurements of intracellular Ca2+ concentration ([Ca2+]i) and membrane currents in myocytes freshly isolated from the human saphenous vein. At a holding potential of –60 mV, ATP (10 M) elicited a transient inward current and increased [Ca2+]i. These effects of ATP were inhibited by ,-methylene adenosine 5-triphosphate (AMPCPP, 10 M). The ATP-gated current corresponded to a non-selective cation conductance allowing Ca2+ entry. The ATP-induced [Ca2+]i rise was abolished in Ca2+-free solution and was reduced to 30.1±5.5% (n=14) of the control response when ATP was applied immediately after caffeine, and to 23.7±3.8% (n=11) in the presence of thapsigargin. The Ca2+-induced Ca2+ release blocker tetracaine inhibited the rise in [Ca2+]i induced by both caffeine and ATP, with apparent inhibitory constants of 70 M and 100 M, respectively. Of the ATP-induced increase in [Ca2+]i 29.3±3.9% (n=8) was tetracaine resistant. It is concluded that the effects of ATP in human saphenous vein myocytes are only mediated by activation of P2x receptor channels. The ATP-induced [Ca2+]i rise is due to both Ca2+ entry and Ca2+ release activated by Ca2+ ions that enter the cell through P2x receptor channels. 相似文献