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Geyti CS Odgaard E Overgaard MT Jensen ME Leipziger J Praetorius HA 《Pflügers Archiv : European journal of physiology》2008,455(6):1105-1117
Renal epithelia can be provoked mechanically to release nucleotides, which subsequently increases the intracellular Ca2+ concentration [Ca2+]i through activation of purinergic (P2) receptors. Cultured cells often show spontaneous [Ca2+]i oscillations, a feature suggested to involve nucleotide signalling. In this study, fluo-4 loaded Madin–Darby canine kidney
(MDCK) cells are used as a model for quantification and characterisation of spontaneous [Ca2+]i increases in renal epithelia. Spontaneous [Ca2+]i increases occurred randomly as single cell events. During an observation period of 1 min, 10.9 ± 6.7% (n = 23) of the cells showed spontaneous [Ca2+]i increases. Spontaneous adenosine triphosphate (ATP) release from MDCK cells was detected directly by luciferin/luciferase.
Scavenging of ATP by apyrase or hexokinase markedly reduced the [Ca2+]i oscillatory activity, whereas inhibition of ecto-ATPases (ARL67156) enhanced the [Ca2+]i oscillatory activity. The association between spontaneous [Ca2+]i increases and nucleotide signalling was further tested in 132–1N1 cells lacking P2 receptors. These cells hardly showed any
spontaneous [Ca2+]i increases. Transfection with either hP2Y6 or hP2Y2 receptors revealed a striking degree of oscillations. Similar spontaneous [Ca2+]i increases were observed in freshly isolated, perfused mouse medullary thick ascending limb (mTAL). The oscillatory activity
was reduced by basolateral apyrase and substantially lower in mTAL from P2Y2
knock out mice (0.050 ± 0.020 events per second, n = 8) compared to the wild type (0.147 ± 0.018 events per second, n = 9). These findings indicate that renal epithelia spontaneously release nucleotides leading to P2-receptor-dependent [Ca2+]i oscillations. Thus, tonic nucleotide release is likely to modify steady state renal function.
C. S. Geyti and E. Odgaard contributed equally to the publication. 相似文献
3.
Kirischuk S Kettenmann H Verkhratsky A 《Pflügers Archiv : European journal of physiology》2007,454(2):245-252
Effects of glutamate and kainate (KA) on Bergmann glial cells were investigated in mouse cerebellar slices using the whole-cell
configuration of the patch-clamp technique combined with SBFI-based Na+ microfluorimetry. l-Glutamate (1 mM) and KA (100 μM) induced inward currents in Bergmann glial cells voltage-clamped at −70 mV. These currents
were accompanied by an increase in intracellular Na+ concentration ([Na+]i) from the average resting level of 5.2 ± 0.5 mM to 26 ± 5 mM and 33 ± 7 mM, respectively. KA-evoked signals (1) were completely
blocked in the presence of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 μM), an antagonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic
acid (AMPA)/KA ionotropic glutamate receptors; (2) reversed at 0 mV, and (3) disappeared in Na+-free, N-methyl-D-glucamine (NMDG+)-containing solution, but remained almost unchanged in Na+-free, Li+-containing solution. Conversely, l-glutamate-induced signals (1) were marginally CNQX sensitive (∼10% inhibition), (2) did not reverse at a holding potential
of +20 mV, (3) were markedly suppressed by Na+ substitution with both NMDG+ and Li+, and (4) were inhibited by d,l-threo-β-benzyloxyaspartate. Further, d-glutamate, l-, and d-aspartate were also able to induce Na+-dependent inward current. Stimulation of parallel fibres triggered inward currents and [Na+]i transients that were insensitive to CNQX and MK-801; hence, we suggested that synaptically released glutamate activates glutamate/Na+ transporter in Bergmann glial cells, which produces a substantial increase in intracellular Na+ concentration. 相似文献
4.
Hans Oberleithner Florian Lang Georg Messner Wenhui Wang 《Pflügers Archiv : European journal of physiology》1984,402(3):272-280
Transepithelial H+ transport was studied in diluting segments of the isolated-perfused kidney ofrana esculenta. The experiments were performed in controls as well as in K+-adapted and Na+-adapted animals (exposed to 50 mmol/l KCl or NaCl, resp. for at least 3 days). Conventional and single-barreled, liquid ion-exchanger H+-sensitive microelectrodes were applied in the tubule lumen to evaluate transepithelial H+ net flux (J
te
H
) as well as limiting transepithelial electrical and H+ electrochemical potential differences (PD
te
,E
te
H
) and luminal pH at zero net flux conditions. The measurements were made in absence (control) and presence of furosemide (5·10–5 mol/l) or amiloride (10–3 mol/l).
E
te
H
(lumen positive vs ground) was 19±3 mV in controls, 43±3 mV in K+ adapted but about zero in Na+ adapted animals. Using the correspondingPD
te
-values, steady state luminal pH of 7.63±0.05, 7.13±0.05 and 8.02±0.02 was calculated for the respective groups of animals (peritubular pH 7.80). In parallel, significant secretoryJ
te
H
(from blood to lumen) was found in controls (14±2 pmol·cm–2·S–1) which was stimulated by K+ adaptation (61±8 pmol·cm–2·s–1) but reversed in direction by Na+-adaptation (–8±1 pmol·cm–2·s–1). Amiloride inhibited secretoryJ
te
H
. Elimination of the lumen positivePD
te
by furosemide did not affect significantlyE
te
H
andJ
te
H
in control and K+ adapted animals but abolished reabsorptiveJ
te
H
in Na+ adapted animals.We conclude that in frog diluting segment H+ secretion is an active, amiloride-sensitive, furosemide-insensitive transport process. The data are consistent with luminal Na+/H+ exchange. The activity of this system depends critically on the metabolic state of the animal.Parts of the data were presented at the 16th Ann. Meeting of the Am. Soc. Nephrol., Washington (1983)This work was supported by österr. Forschungsrat, Proj. No.: 4366 and by Dr. Legerlotz Stiftung 相似文献
5.
Poulsen AN Klausen TL Pedersen PS Willumsen NJ Frederiksen O 《Pflügers Archiv : European journal of physiology》2005,450(4):227-235
We investigated purinergic receptors involved in ion transport regulation in the intact rabbit nasal airway epithelium. Stimulation of apical membrane P2Y receptors with ATP or UTP (200 M) induced transient increases in short-circuit current (Isc) of 13 and 6% followed by sustained inhibitions to 8 and 17% below control level, respectively. Serosal application of nucleotides had no effect. The ATP-induced response appeared to involve additional activation of apical adenosine (P1) and P2X receptors. The inhibitory effect of ATP and UTP on Isc was eliminated by pretreatment with amiloride (100 M), while the stimulatory effect was potentiated, indicating that ATP and UTP inhibit Na+ and stimulate Cl– current. Ionomycin (1 M) induced responses similar to UTP and ATP and desensitized the epithelium to the nucleotides, indicating involvement of intracellular Ca2+ (Ca2+i). Furthermore, ATP, UTP and ionomycin induced 21, 24, and 21% decreases, respectively, in transepithelial conductance. Measurements of unidirectional isotope fluxes showed a 39% decrease in the dominant net Na+ absorption in response to ATP, while the smaller net Cl– secretion increased only insignificantly and unidirectional Cl– fluxes decreased significantly. The results suggest that nucleotides released to the airway surface liquid exert an autocrine regulation of epithelial NaCl absorption mainly by inhibiting the amiloride-sensitive epithelial Na+ channel (ENaC) and paracellular anion conductance via a P2Y receptor-dependent increase in Ca2+i, while stimulation of Cl– secretion is of minor importance. 相似文献
6.
David T. Thwaites Gordon T. A. McEwan Barry H. Hirst Nicholas L. Simmons 《Pflügers Archiv : European journal of physiology》1993,425(1-2):178-180
Net transepithelial transport (and cellular accumulation) of the dipeptide glycylsarcosine (Gly-Sar), across the apical membrane of human intestinal Caco-2 epithelia, is driven by a proton gradient (Na+-free conditions) and displays saturation kinetics (Km 17.4±5.1 mM, Vmax of 92.8±15.6 nmol.cm–2.h–1). Net Gly-Sar transport is associated with the stimulation of an inward short-circuit current (Isc). This dipeptide-stimulated Isc is observed in both Na+-containing and Na+-free conditions, is stimulated by apical acidity, and displays saturation kinetics (in Na+-free media at apical pH 6.0, Km of 13.6±4.5 mM and a Vmax of 284.1±39.3 nmol.cm–2.h–1). The maximal capacities of Gly-Sar transport and Isc suggest a dipeptide/proton stoichiometry greater than unity (13). 相似文献
7.
Diana Faria Rainer Schreiber Karl Kunzelmann 《Pflügers Archiv : European journal of physiology》2009,457(6):1373-1380
It has been reported that the cystic fibrosis transmembrane conductance regulator (CFTR) can be activated through cAMP- and
protein kinase A-independent pathways involving GTP-binding proteins and an unknown kinase. In this study, we further examined
how G protein-coupled pathways regulate CFTR. We demonstrate that stimulation of purinergic P2Y2 receptors in CFTR-expressing oocytes and in airway epithelial cells activates CFTR Cl− currents. Activation of CFTR Cl− currents via P2Y2 was inhibited by CFTRinh-172 and was independent of intracellular Ca2+, protein kinase C, or calmodulin-dependent kinase (CAMK). However, activation of CFTR was suppressed by inhibition of phospholipase
C and by the nonselective protein kinase inhibitor staurosporine. Activation of CFTR through P2Y2 receptors was enhanced when Gi proteins were inhibited by pertussis toxin. Inhibition of protein kinase A and of protein kinases downstream of P2Y2 receptors such as mitogen-activated protein kinases, tyrosine kinase, or c-src kinase did not interfere with activation of CFTR. The present results demonstrate an antagonistic regulation of CFTR by P2Y2 receptors: CFTR is inhibited by stimulation of Gi proteins and is activated by stimulation of Gq/11/PLC and an unknown downstream protein kinase. 相似文献
8.
Marguerite Hatch Robert W. Freel 《Pflügers Archiv : European journal of physiology》1988,411(3):333-338
Electrolyte transport across rabbit caecal epithelium was investigated in vitro using conventional shortcircuiting and radioisotope
techniques. In standard saline the caecum exhibited a relatively high short-circuit current (I
sc=4.4 μEq · cm−2 · h−1) and conductance (6.43 mS · cm−2). Both sodium and chloride were absorbed (J
net
Na
=6.40 andJ
net
Cl
=3.40 μEq · cm−2 · h−1) and potassium was secreted (J
net
K
=−0.5 μEq · cm−2 · h−1). Removal of Na+ abolishedI
sc andJ
net
Cl
whereas removal of Cl− reducedJ
net
Na
to 2.92 μEq · cm−2 · h−1 but did not alterI
sc. In HCO
3
−
free salines containing 10−4 M acetazolamideJ
net
Cl
was abolished andJ
net
Na
andI
sc were reduced to 2.3 and 2.5 μEq · cm−2 · h−1 respectively. A positive residual ion flux (∼ 1 μEq · cm−2 · h−1) was detected in standard and Cl−-free salines but not in Na+-free or HCO
3
−
buffers. Mucosal amiloride (10−3 M) decreased net Na+ and Cl− absorption but did not decreaseI
sc. Mucosal DIDS (10−4 M) decreasedJ
net
Cl
while mucosal bumetanide (10−4 M) did not affect any of the measured parameters. Finally, addition of theophylline (8 mM) stimulated Cl− secretion and increasedI
sc. It is concluded that net sodium absorption by caecal epithelia occurs by both electrogenic and electroneutral mechanisms
whereas net chloride absorption occurs only by an electroneutral process. Coupling of the absorptive fluxes of Na+ and Cl− may result from Na+/H+ and Cl−/HCO
3
−
antiport systems in this tissue. Finally, it is proposed that up to half of theI
sc is due to a Na+-dependent secretion of bicarbonate ion. 相似文献
9.
Ca2+- and swelling-induced activation of ion conductances in bronchial epithelial cells 总被引:2,自引:0,他引:2
T. Koslowsky T. Hug D. Ecke P. Klein R. Greger D. C. Gruenert K. Kunzelmann 《Pflügers Archiv : European journal of physiology》1994,428(5-6):597-603
The present study was performed to examine Ca2+-dependent and cell-swelling-induced ion conductances in a polarized bronchial epithelial cell line (16HBE14o-). Whole-cell currents were measured in fast and slow whole-cell patch-clamp experiments in cells grown either on filters or on coated plastic dishes. In addition the transepithelial voltage (V
te) and resistance (R
te) were measured in confluent monolayers. Resting cells had a membrane voltage (V
m) of –36±1.1 mV (n=137) which was mainly caused by K+ and Cl– conductances and to a lesser extent by a Na+ conductance. V
te was apical-side-negative after stimulation. Equivalent short-circuit current (I
sc = V
te/R
te) was increased by the secretagogues histamine (0.1 mmol/l), bradykinin (0.1–10 mol/l) and ATP (0.1–100 mol/l). The histamine-induced I
sc was blocked by either basolateral diphenhydramine (0.1 mmol/l, n=4) or apical cimetidine (0.1 mmol/l, n=4). In fast and slow whole-cell recordings ATP and bradykinin primarily activated a transient K+ conductance and hyperpolarized V
m. This effect was mimicked by the Ca2+ ionophore ionomycin (1 mol/l, n=11). Inhibition of the bradykinin-induced I
sc by the blocker HOE140 (1 mol/l, n=3) suggested the presence of a BK2 receptor. The potency sequence of different nucleotide agonists on the purinergic receptor was UTP ATP > ITP > GTP CTP [,-methylene] ATP 2-methylthio-ATP = 0 and was obtained in I
sc measurements and patch-clamp recordings. This suggests the presence of a P2u receptor. Hypotonic cell swelling activated both Cl– and K+ conductances. The Cl– conductance was only slightly inhibited by 4,4-diisothiocyanatostilbene-2,2-disulphonic acid (0.5 mmol/ l, n=3). These data indicate that 16HBE140- bronchial epithelial cells, which are known to express high levels of cystic fibrosis transmembrane conductance regulator protein, form a secretory epithelium. While hypotonic cell swelling activates both K+ and Cl– channels, the Ca2+-induced Cl– secretion is due mainly to activation of basolateral K+ channels. 相似文献
10.
Claude Penel Corinne Gérard Jean Mauchamp Bernard Verrier 《Pflügers Archiv : European journal of physiology》1989,414(5):509-515
When cultured on collagen coated nitrocellulose filters, thyroid epithelial cells form morphologically and functionally polarized monolayers. The bioelectric parameters of these monolayers were measured after mounting in Ussing chambers; transepithelial potential (V
ab), short circuit current (I
sc) and transepithelial resistance were respectively 12±1 mV (apical side negative), 3.8±0.2 A cm–2 and 3250±214 cm2 (mean±SEM,n=75). Eighty two percent of the short circuit current was related to sodium absorption as shown by inhibition by apical amiloride (K
m=0.2 M) and by basal ouabain (K
1/2=0.3 M). Amphotericin B (5–25 g/ml) added to the apical bath increasedI
sc suggesting an apical rate-limiting step. Step by step replacement of choline by Na+ in a Na+-free medium resulted in a progressive increase inV
ab andI
sc with half maximal effect at 20±1 mM Na+. Thyrotropin (TSH) increasedI
sc andV
ab in a biphasic way with a transient maximum after 5 min and a plateau after 20 min (about four times the basal level at 100 U/ml TSH). This increase in sodium transport was also inhibited by apical amiloride. Thus, in culture, the thyroid cell monolayer behaves as a tight sodium absorbing epithelium controlled by TSH, with a rate limiting apical sodium channel as the entry mechanism and a basolateral Na+, K+-ATPase as the electromotive force. 相似文献
11.
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
12.
Electrophysiological study of transport systems in isolated perfused pancreatic ducts: properties of the basolateral membrane 总被引:3,自引:0,他引:3
In order to study the mechanism of pancreatic HCO
3
–
transport, a perfused preparation of isolated intra-and interlobular ducts (i.d. 20–40 m) of rat pancreas was developed. Responses of the epithelium to changes in the bath ionic concentration and to addition of transport inhibitors was monitored by electrophysiological techniques. In this report some properties of the basolateral membrane of pancreatic duct cells are described. The transepithelial potential difference (PDte) in ducts bathed in HCO
3
–
-free and HCO
3
–
-containing solution was –0.8 and –2.6 mV, respectively. The equivalent short circuit current (Isc) under similar conditions was 26 and 50 A·cm–2. The specific transepithelial resistance (Rte) was 88 cm2. In control solutions the PD across the basolateral membrane (PDbl) was –63±1 mV (n=314). Ouabain (3 mmol/l) depolarized PDbl by 4.8±1.1 mV (n=6) within less than 10 s. When the bath K+ concentration was increased from 5 to 20 mmol/l, PDbl depolarized by 15.9±0.9 mV (n=50). The same K+ concentration step had no effect on PDbl if the ducts were exposed to Ba2+, a K+ channel blocker. Application of Ba2+ (1 mmol/l) alone depolarized PDbl by 26.4±1.4 mV (n=19), while another K+ channel blocker TEA+ (50 mmol/l) depolarized PDbl only by 7.7±2.0 mV (n=9). Addition of amiloride (1 mmol/l) to the bath caused 3–4 mV depolarization of PDbl. Furosemide (0.1 mmol/l) and SITS (0.1 mmol/l) had no effect on PDbl. An increase in the bath HCO
3
–
concentration from 0 to 25 mmol/l produced fast and sustained depolarization of PDbl by 8.5±1.0 mV (n=149). It was investigated whether the effect of HCO
3
–
was due to a Na++-dependent transport mechanism on the basolateral membrane, where the ion complex transferred into the cell would be positively charged, or whether it was due to decreased K+ conductance caused by lowered intracellular pH. Experiments showed that the HCO
3
–
effect was present even when the bath Na+ concentration was reduced to a nominal value of 0 mmol/l. Similarly, the HCO
3
–
effect remained unchanged after Ba2+ (5 mmol/l) was added to the bath. The results indicate that on the basolateral membrane of duct cells there is a ouabain sensitive (Na++K+)-ATPase, a Ba2+ sensitive K+ conductance and an amiloride sensitive Na+/H+ antiport. The HCO
3
–
effect on PDbl is most likely due to rheogenic anion exit across the luminal membrane. 相似文献
13.
Williams IA Xiao XH Ju YK Allen DG 《Pflügers Archiv : European journal of physiology》2007,454(6):903-912
Intracellular Na+ concentration ([Na+]i) rises in the heart during ischemia, and on reperfusion, there is a transient rise followed by a return toward control. These
changes in [Na+]i contribute to ischemic and reperfusion damage through their effects on Ca2+ overload. Part of the rise of [Na+]i during ischemia may be caused by increased activity of the cardiac Na+/H+ exchanger (NHE1), activated by the ischemic rise in [H+]i. In support of this view, NHE1 inhibitors reduce the [Na+]i rise during ischemia. Another possibility is that the rise of [Na+]i during ischemia is caused by Na+ influx through channels. We have reexamined these issues by use of two different NHE1 inhibitors, amiloride, and zoniporide,
in addition to tetrodotoxin (TTX), which blocks voltage-sensitive Na+ channels. All three drugs produced cardioprotection after ischemia, but amiloride (100 μM) and TTX (300 nM) prevented the
rise in [Na+]i during ischemia, whereas zoniporide (100 nM) did not. Both amiloride and zoniporide prevented the rise of [Na+]i on reperfusion, whereas TTX was without effect. In an attempt to explain these differences, we measured the ability of the
three drugs to block Na+ currents. At the concentrations used, TTX reduced the transient Na+ current (I
Na) by 11 ± 2% while amiloride and zoniporide were without effect. In contrast, TTX largely eliminated the persistent Na+ current (I
Na,P) and amiloride was equally effective, whereas zoniporide had a substantially smaller effect reducing I
Na,P to 41 ± 8%. These results suggest that part of the effect of NHE1 inhibitors on the [Na+]i during ischemia is by blockade of I
Na,P. The fact that a low concentration of TTX eliminated the rise of [Na+]i during ischemia suggests that I
Na,P is a major source of Na+ influx in this model of ischemia. 相似文献
14.
G. Capasso R. Unwin F. Ciani G. De Tommaso M. Vinciguerra F. Russo N. G. De Santo 《Pflügers Archiv : European journal of physiology》1994,429(1):44-49
The loop of Henle (LOH) reabsorbs approximately 15% of filtered HCO
3
−
via a luminal Na+-H+ exchanger and H+ATPase. During acute metabolic alkalosis (AMA) induced by i.v. HCO
3
−
infusion, we have observed previously inhibition of LOH net HCO
3
−
reabsorption
, which contributes to urinary elimination of the HCO
3
−
load and correction of the systemic alkalosis. To determine whether the activities of the Na+-H+ exchanger and/or H+-ATPase are reduced during AMA, two inhibitors believed to be sufficiently specific for each transporter were delivered by
in vivo LOH microperfusion during AMA. AMA reduced LOH
from 205.0±0.8 to 96.2±11.8 pmol · min−1 (P<0.001). Luminal perfusion with bafilomycin A1 (10−4 mol · l−1) caused a further reduction in
by 83% and ethylisopropylamiloride (EIPA; 5.10−4 mol · l−1) completely abolished net HCO
3
−
reabsorption. The combination of bafilomycin A1 and EIPA in the luminal perfusate was additive, resulting in net HCO
3
−
secretion (−66.6±20.8 pmol · min−1;P<0.001) and abolished net fluid reabsorption (from 5.0±0.6 during AMA to 0.2±1.1 nl · min−1;P<0.001). To establish whether HCO
3
−
secretion via luminal stilbenesensitive transport mechanism participates in LOH adaptation to AMA, we added diisothiocyanato-2,2′-stilbenedisulphonate
(DIDS; 10−4 mol · l−1) to the perfusate. No effect was found. However, when the same LOH were exposed to luminal DIDS for more than 10 min, the
direction of net HCO
3
−
movement was reversed and net HCO
3
−
secretion occurred:
changed from 90.6±8.8 to −91.9±34.1 pmol · min−1;P<0.01, an effect that was not observed in the control state (undisturbed acid-base balance). Thus, during AMA, neither the
luminal Na+-H+ exchanger nor the H+-ATPase are noticeably suppressed. However, pharmacological elimination of both transporters, as well as prolonged exposure
of the tubular lumen to DIDS, induced net HCO
3
−
secretion. This secretory flux may reflect paracellular backflux due to the steeper blood to lumen HCO
3
−
concentration gradient that presumably prevails in AMA. 相似文献
15.
A. Di Stefano M. Wittner R. Nitschke R. Braitsch R. Greger C. Bailly C. Amiel N. Roinel C. de Rouffignac 《Pflügers Archiv : European journal of physiology》1990,417(2):161-167
The effect of parathyroid hormone (PTH) on transepithelial Na+, Cl–, K+, Ca2+ and Mg2+ transport was investigated in isolated perfused cortical thick ascending limbs (cTAL) and that of human calcitonin (hCT) was tested in both cortical and medullary thick ascending limbs (mTAL) of the mouse nephron. The transepithelial ion net fluxes (J
x) were determined by electron probe analysis of the perfused and collected fluids. Simultaneously, the transepithelial voltage (PDte) and resistance (R
te) were recorded. In cTAL segments, PTH and hCT significantly stimulated the reabsorption of Na+, Cl–, Ca2+ and Mg2+. hCT generated a net K+ secretion towards the lumen and PTH tended to exert the same effect. Neither PDte nor R
te were significantly altered by either PTH or hCT. However, in the post-experimental period a significant decrease in PDte was noted. Time control experiments carried out under similar conditions revealed a significant decrease in PDte with time, which could have masked the hormonal response. In mTAL segments, Mg2+ and Ca2+ transport was close to zero. hCT did not exert any detectable effect on either PDte or J
Cl
–, J
Na
+
J
K
+, J
Mg
2+ and J
Ca
2+ in these segments. In conclusion, our data demonstrate that PTH and hCT stimulate NaCl reabsorption as well as Mg2+ and Ca2+ reabsorption in the cTAL segment of the mouse. These data are in agreement with and extend data obtained in vivo in the rat. 相似文献
16.
Mareile Weigt Paul Dietl Stefan Silbernagl Hans Oberleithner 《Pflügers Archiv : European journal of physiology》1987,408(6):609-614
Increased chronic intake of K+ induced H+ and K+ secretion in amphibian distal tubule, paralleled by an elevation of plasma aldosterone. The present experiments test whether the mineralocorticoid hormone is responsible for the alteration of ion transport. The blood capillaries of the isolated kidneys of NaCl-adapted (i.e. aldosterone-suppressed)Rana pipiens were perfused with HEPES-buffered amphibian Ringer solution (pH 7.8). Limiting intraluminal pH (pH1u) was measured continuously with pH-sensitive microelectrodes while aldosterone (3·10–7 to 3·10–6 mol/l) was applied in the peritubular perfusate. Concomitant with a decrease of the lumen-positive transepithelial potential (V
te) from 8.5±1.1 mV to 4.0±0.6 mV pH1u dropped from 7.73±0.02 to a new steady-state value of 7.17±0.05 within 60 to 180 min of aldosterone administration. Significant luminal acidification occurred already 20 min after application of aldosterone. Luminal addition of 10–3 mol/l amiloride reversed luminal acidification to a pH1u of 7.68±0.04; at the same timeV
te recovered partially. Pretreatment of the distal tubules with spironolactone prevented the aldosterone-induced acidification of the tubule fluid. We conclude that in early distal tubule of the amphibian kidney aldosterone — after interaction with cytoplasmic receptors — activates the luminal, amiloride-inhibitable Na+/H+ exchanger. This mechanism could explain enhanced H+ secretion found in the K+ adapted animal. 相似文献
17.
G. Planelles T. Anagnostopoulos 《Pflügers Archiv : European journal of physiology》1992,421(4):307-313
To find out the mechanism(s) underlying NaCl absorption in the distal tubule of Necturus, we devised a variant of the split-drop technique. Following injection an oil column, subsequently split by a NaCl solution isotonic to plasma, a double-barrelled microelectrode (conventional/selective to Na+ or to Cl– ions) recorded Na+ (
Na) or Cl– (
Cl) activity and transepithelial potential (V
te). Paired control/low-Na+ solutions yielded reabsorptive half-times (t
1/2) of 0.68±0.11 min and 7.6±1.8 min respectively; corresponding V
te values were –22.2±4.0 mV and –7.6±1.9 mV. t
1/2 values of control versus low-Cl– solutions were 0.77±0.32 min and 6.5±1.7 min respectively, whereas respective V
te values were not different from one another: –23.8±4.3 mV versus –18.8±5.5 mV. Nominally K+-free solutions or bumetanide, 10 mol/l, did not alter t
1/2 or V
te, with regard to the paired control. Amiloride, 5 mol/l or 2 mmol/l, failed to decrease t
1/2 or to lower V
te; apparently, the role of a Na+/H+ antiport does not contribute significantly to NaCl absorption. Furosemide, 0.1 mmol/l, reduced t
1/2 by 54% with regard to the control state. Determination of t
1/2 as a function of increasing hydrochlorothiazide concentrations revealed apical high- and low-affinity sites, estimated at 0.56 mol/l and 0.115 mmol/l respectively. Taken together these observations indicate that NaCl absorption is predominantly carried out by an electroneutral Na+-Cl– cotransport. 相似文献
18.
Albrecht Schwab Hans Oberleithner 《Pflügers Archiv : European journal of physiology》1988,411(3):268-272
In frog diluting segment transepithelial K+ net flux (J
te
K
) occurs via trans- and paracellular transport routes. Inhibition of transcellular K+ transport disclosesJ
te
K
across the shunt-pathway. By means of K+-sensitive microelectrodes we have measured secretoryJ
te
K
induced by an acute K+ load, in the diluting segment of the isolated and doublyperfused frog kidney. Transcellular K+ transport was inhibited by blocking the luminal K+ permeability either directly by barium or indirectly by the diuretic drug amiloride (via intracellular acidification induced
by inhibition of Na+/H+ exchange), by the the Na+/K+ pump inhibitor ouabain or by inducing an acute acid load. All experimental maneouvers led to a reduction of secretoryJ
te
K
to about 50% of the controlJ
te
K
. The apparent permeability coefficient for K+ of this nephron portion after inhibition of transcellular secretoryJ
te
K
was reduced to a similar extent. We conclude: In frog diluting segment the ratio of trans- over paracellularJ
te
K
is close to unity. This ratio represents a minimum estimate because inhibition of the transcellular K+ pathway by barium, amiloride or an acute acid load may have been incomplete. Acidosis and/or amiloride exert large antikaliuretic
effects due to the inhibition of the luminal K+ permeability. 相似文献
19.
ATP increases [Ca2+]i and ion secretion via a basolateral P2Y-receptor in rat distal colonic mucosa 总被引:1,自引:0,他引:1
J. Leipziger D. Kerstan R. Nitschke R. Greger 《Pflügers Archiv : European journal of physiology》1997,434(1):77-83
Under resting conditions the mammalian distal colon is a NaCl-absorptive epithelium. NaCl absorption occurs at surface cells
in colonic crypts. Intracellular Ca2+ or cAMP are important second messengers that activate NaCl secretion, a function that is most pronounced in crypt bases. In
the present study we examined the effect of extracellular ATP on isolated crypts of rat distal colon using the fura-2 technique.
Intracellular Ca2+ ([Ca2+]i) was measured spectrofluorimetrically either by photon counting or video imaging. ATP reversibly increased [Ca2+]i in crypt base cells with an EC50 of 4.5 μmol/l (n = 11). This [Ca2+]i increase was composed of an initial peak, reflecting intracellular store release, and a secondary plateau phase reflecting
transmembrane influx. Digital video imaging revealed that agonist-induced [Ca2+]i elevations were most marked at the crypt base. In the middle part of the crypt ATP induced smaller increases of [Ca2+]i (peak and plateau) as compared to basal cells and in surface cells this [Ca2+]i transient was even further reduced. Attempts to identify the relevant P2-receptor demonstrated the following rank order of potency: 2MeS-ATP > ADP ≥ ATP >> AMP > UTP > AMP-PCP > adenosine. In Ussing
chamber experiments ATP (1 mmol/l) functioned as a secretagogue, increasing transepithelial voltage (V
te) and equivalent short-circuit current (I
sc): ΔI
sc = –36.4 ± 5.4 μA/cm2, n = 17. Adenosine itself (1 mmol/l) induced an increase of I
sc of similar magnitude to that induced by ATP: ΔI
sc = –55.1 ± 8.4 μA/cm2, n = 9. The effect of adenosine, but not that of ATP, was fully inhibited by the A1/A2-receptor antagonist 8-(p-sulphophenyl)theophylline, 0.5 mmol/l, n = 4. Together these data indicate that: (1) basolateral ATP induces [Ca2+]i in isolated rat colonic crypts and acts as a secretagogue in the distal rat colon; (2) a basolateral P2Y-receptor is responsible
for this ATP-induced NaCl secretion; (3) the ability of ATP to increase I
sc in Ussing chamber experiments is not mediated via adenosine; and (4) the agonist-induced [Ca2+]i signals are mostly located in the crypt base, which is the secretory part of the colonic crypt.
Received: 17 September 1996 / Received after revision: 20 January 1997 / Accepted: 28 January 1997 相似文献
20.
Mitochondrial Ca2+ plays important roles in the regulation of energy metabolism and cellular Ca2+ homeostasis. In this study, we characterized mitochondrial Ca2+ accumulation in Syrian hamster hearts with hereditary cardiomyopathy (strain BIO 14.6). Exposure of isolated mitochondria
from 70 nM to 30 μM Ca2+ ([Ca2+]o) caused a concentration-dependent increase in intramitochondrial Ca2+ concentrations ([Ca2+]m). The [Ca2+]m was significantly lower in cardiomyopathic (CMP) hamsters than in healthy hamsters when [Ca2+]o was higher than 1 μM and a decrease of about 52% was detected at [Ca2+]o of 30 μM (916 ± 67 nM vs 1,932 ± 132 nM in control). A possible mechanism responsible for the decreased mitochondrial Ca2+ uptake in CMP hamsters is the depolarization of mitochondrial membrane potential (Δψ
m). Using a tetraphenylphosphonium (TPP+) electrode, the measured Δψ
m in failing heart mitochondria was −136 ± 1.5 mV compared with −159 ± 1.3 mV in controls. Analyses of mitochondrial respiratory
chain demonstrated a significant impairment of complex I and complex IV activities in failing heart mitochondria. In summary,
a less negative Δψ
m resulting from defects in the respiratory chain may lead to attenuated mitochondrial Ca2+ accumulation, which in turn may contribute to the depressed energy production and myocardial contractility in this model
of heart failure. In addition to other known impairments of ion transport in sarcoplasmic reticulum and plasma membrane, results
from this paper on mitochondrial dysfunctions expand our understanding of the molecular mechanisms leading to heart failure. 相似文献