Volume regulation and intracellular calcium in the rabbit proximal convoluted tubule

The hypothesis that an increase of calcium leads to activation of calcium-activated ionic conductances during cell swelling was examined in the isolated perfused proximal convoluted tubule of the rabbit. Reduction of bath and luminal osmolality by 90 mosmol/kgH2O caused the cells to swell by 23.6 +/- 1.5% (n = 5) and intracellular calcium to rise from 227 +/- 35 to 347 +/- 60 nM (n = 6). Both these increases were transient, with volume decreasing to 5.5 +/- 1.2% above control and intracellular calcium concentration decreasing to 272 +/- 46 nM after 5-9 min. The addition of glucose and alanine to the tubule lumen to increase transcellular sodium transport caused a sustained increase in cell volume of 15.6 +/- 3.4% (n = 4). In parallel experiments, no significant increase in intracellular calcium concentration was observed. Addition of 1 microM of the calcium ionophore, ionomycin, reversibly increased intracellular calcium by 224 +/- 60 nM from a control value of 301 +/- 29 nM (n = 7) and reversibly depolarized the basolateral membrane by 3.6 +/- 0.9 mV (n = 5). However, there was no initial increase in the apparent transference number for potassium or chloride and no significant change in cell volume. We conclude from these observations that the sustained increase in basolateral potassium conductance observed when cells are swollen by hypotonicity or increased sodium transport (J. S. Beck and D. J. Potts. J. Physiol. Lond. 425: 369-378, 1990) is not due to a calcium-activated potassium conductance.

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Relationship between sodium transport and intracellular ATP in isolated perfused rabbit proximal convoluted tubule

AJP Renal Physiology ◽

10.1152/ajprenal.1991.261.4.f634 ◽

1991 ◽

Vol 261 (4) ◽

pp. F634-F639 ◽

Cited By ~ 11

Author(s):

J. S. Beck ◽

S. Breton ◽

H. Mairbaurl ◽

R. Laprade ◽

G. Giebisch

Keyword(s):

Potassium Channels ◽

Cell Volume ◽

Intracellular Ph ◽

Sodium Transport ◽

Sodium Pump ◽

Basolateral Membrane ◽

Potassium Conductance ◽

Transference Number ◽

Proximal Convoluted Tubule ◽

A Cell

The effect of alterations in sodium transport on cell ATP content and pH in the isolated perfused proximal convoluted tubule (PCT) of the rabbit was examined. Stimulating sodium transport by the addition of luminal glucose and alanine decreased cell ATP from 4.44 +/- 0.93 to 2.69 +/- 0.62 mM (n = 4), increased intracellular pH by 0.13 +/- 0.02 (n = 7), and increased cell volume by 0.10 +/- 0.02 nl/mm (n = 4). Blocking the sodium pump with 10(-4) M strophanthidin in tubules in which sodium transport had been stimulated increased cell ATP from 2.04 +/- 0.24 to 2.42 +/- 0.32 mM (n = 6). In parallel experiments the same dose of strophanthidin depolarized the basolateral membrane from -52.6 +/- 1.9 to -6.4 +/- 1.6 mV, depolarized the transepithelial potential from -3.2 +/- 0.3 to -0.1 +/- 0.1 mV, and reduced the basolateral membrane potassium transference number from 0.47 to 0.26 indicating a reduction in basolateral potassium conductance. Since strophanthidin caused a cell alkalinization of 0.15 +/- 0.03, this latter effect cannot be due to changes of intracellular pH. Strophanthidin caused no change in cell volume over the period studied, suggesting that stretch-activated potassium channels are not involved either. Instead, potassium conductance inhibition may be the result of the closure of ATP-sensitive potassium channels. These same channels might thus be partly responsible for the increase in potassium conductance commonly observed during stimulation of sodium transport.

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Activity-induced elevations of intracellular calcium concentration in pyramidal and nonpyramidal cells of the CA3 region of rat hippocampal slice cultures

Journal of Neurophysiology ◽

10.1152/jn.1992.68.3.961 ◽

1992 ◽

Vol 68 (3) ◽

pp. 961-963 ◽

Cited By ~ 20

Author(s):

T. Knopfel ◽

B. H. Gahwiler

Keyword(s):

Intracellular Calcium ◽

Time Course ◽

Calcium Concentration ◽

Potassium Conductance ◽

Pyramidal Cells ◽

Calcium Transients ◽

Intracellular Calcium Concentration ◽

Calcium Signal ◽

Cell Somata ◽

Ca3 Region

1. Depolarization-induced elevations of intracellular calcium concentration ([Ca2+]i) were examined in slice-cultured hippocampal pyramidal and nonpyramidal cells of the CA3 region by combined intracellular and multisite fura-2 recording techniques. 2. In pyramidal cells, spiking activity induced by depolarizing current pulses (200–800 ms) induced transient elevations of somatic as well as of proximal dendritic [Ca2+]i. The calcium signals from the proximal dendrites were larger in amplitude and decayed much faster than those from the soma. Depolarization of presumed interneurons induced comparable somatic and dendritic calcium transients, which decayed faster than those observed in pyramidal cell somata. 3. The calcium transients of pyramidal cells, but not those of nonpyramidal cells, were associated with a slow afterhyperpolarization (sAHP), whose time course was correlated with that of the somatic calcium signal. We conclude that the lack of a sAHP in non-pyramidal cells cannot be explained by the absence of an efficient rise in [Ca2+]i but rather by the absence of the potassium conductance underlying the sAHP in pyramidal cells.

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Inhibition of basolateral potassium conductance by taurine in the proximal convoluted tubule

AJP Renal Physiology ◽

10.1152/ajprenal.1996.271.5.f1012 ◽

1996 ◽

Vol 271 (5) ◽

pp. F1012-F1019 ◽

Cited By ~ 1

Author(s):

S. Breton ◽

F. Belachgar ◽

M. Marsolais ◽

J. Y. Lapointe ◽

R. Laprade

Keyword(s):

Basolateral Membrane ◽

Potassium Conductance ◽

Membrane Conductance ◽

Proximal Convoluted Tubule ◽

Cell Swelling ◽

Partial Recovery ◽

Progressive Decrease ◽

Electrophysiological Properties ◽

The One ◽

Dependent Transport

The effect of taurine on the electrophysiological properties of the basolateral membrane of the rabbit proximal convoluted tubule was examined. Short-duration isosmotic pulses of 40 mM taurine in the bath solution induced basolateral membrane depolarizations (delta Vbl) of 6.44 +/- 0.5 mV, which were reduced by 58% in absence of Na+. In presence of barium and quinine, delta Vbl values were reduced by 55% in Na(+)-containing bath solutions and were completely abolished in Na(+)-free solutions. Continuous addition of taurine into the bath solutions for a period of 5 min induced 1) a decrease in the partial conductance of the basolateral membrane to K+ (tK) from 0.39 to 0.23; 2) an increase in the partial conductance to Cl- (tcl) from 0.055 to 0.172; 3) a rapid and transient increase of the partial conductance mediated by the Na-HCO3 cotransporter (tNaHCO3) from 0.37 to 0.52, followed by a progressive decrease to 0.29; and 4) a depolarization of the basolateral membrane of 16 mV. The absolute membrane conductance mediated by the Na-HCO3 cotransporter was not initially affected by taurine, whereas that to K (GK) initially decreased by a maximal factor of 2 after 1 min, followed by a partial recovery after 5 min, and that to Cl (GCl) increased by a factor of 4. Addition of taurine after a hypotonicity-induced cell swelling produced an inhibition of GK comparable to the one observed under isotonic conditions. These results demonstrate the presence of an electrogenic Na-dependent transport of taurine and indicate that taurine inhibits GK.

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