CYTOSOLIC Ca ION ACTIVITY IN PROXIMAL TUBULAR CELLS OF NECTURUS KIDNEY

Lee, Chin O.; Taylor, Ann; Windhager, Erich E.

doi:10.1016/b978-0-08-026824-8.50048-5

Cited by 3 publications

(5 citation statements)

References 4 publications

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“…At the time of the experiments we were not sure whether the vesicles were right-side or inside out and we wanted to allow sufficient time for equilibration of the internal vesicular calcium concentration. Calcium clearly reduced the permeability of the luminal membrane vesicles, and the half-maximal inhibition calculated from a Hill plot is 0.5/~M, very much within the range of cytosolic calcium activity as measured by ion-selective microelectrodes (31,32,37). We assume that because the permeability of the vesicles is sensitive to calcium in the submicromolar range, and in whole tissue there seems to be little effect of external millimolar calcium on luminal sodium permeability, the effect of calcium in these experiments was exerted on the cytosolic face of the membrane (6).…”

Section: Effect Of Calcium On the Permeability Of The Luminal Membranesupporting

confidence: 56%

“…We recently demonstrated the existence of a sodium-calcium exchanger in the basolateral membrane of toad bladder (5). Also, Lorenzen et al (37) and Lee et al (32) showed that changes in cell calcium activity in Necturus tubule were coupled to the sodium gradient across the serosal membrane. As yet, unfortunately, no measurement of cell calcium as a function of luminal sodium is available.…”

Section: Introductionmentioning

confidence: 83%

“…Only recently has cytosolic calcium activity been measured in epithelia with ion-selective electrodes. Lee and associates (32,37) have measured cell calcium in Necturus proximal tubule under a variety of conditions, including removal of serosal sodium and the addition of ouabain. We had previously performed identical experiments in intact toad bladder and found that the permeability of the luminal membrane was reduced under these conditions.…”

Section: Correlation Between the In Vivo And In Vitro Responsesmentioning

confidence: 99%

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Calcium reduces the sodium permeability of luminal membrane vesicles from toad bladder. Studies using a fast-reaction apparatus.

Chase¹,

Al‐Awqati²

1983

The Journal of General Physiology

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Regulation of the sodium permeability of the luminal membrane is the major mechanism by which the net rate of sodium transport across tight epithelia is varied. Previous evidence has suggested that the permeability of the luminal membrane might be regulated by changes in intracellular sodium or calcium acti¥ities. To test this directly, we isolated a fraction of the plasma membrane from the toad urinary bladder, which contains a fast, amiloridesensitive sodium flux with characteristics similar to those of the native luminal membrane. Using a flow-quench apparatus to measure the initial rate of sodium efflux from these vesicles in the millisecond time range, we have demonstrated that the isotope exchange permeability of these vesicles is very sensitive to calcium. Calcium reduces the sodium permeability, and the half-maximal inhibitory concentration is 0.5 #M, well within the range of calcium activity found in cells. Also, the permeability of the luminal membrane vesicles is little affected by the ambient sodium concentration. These results, when taken together with studies on whole tissue, suggest that cell calcium may be an important regulator of transepithelial sodium transport by its effect on luminal sodium permeability. The effect of cell sodium on permeability may be mediated by calcium rather than by sodium itself.

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Section: Effect Of Calcium On the Permeability Of The Luminal Membranesupporting

confidence: 56%

Section: Introductionmentioning

confidence: 83%

Section: Correlation Between the In Vivo And In Vitro Responsesmentioning

confidence: 99%

See 1 more Smart Citation

Calcium reduces the sodium permeability of luminal membrane vesicles from toad bladder. Studies using a fast-reaction apparatus.

Chase¹,

Al‐Awqati²

1983

The Journal of General Physiology

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“…Our studies suggest that the stoichiometry is also 3 sodium:calcium. 3 Using the value of 3 as the stoichiometry, the open-circuit electrical measurements of Narvarte and Finn (35), the cell calcium activity obtained by Lee (25,26) and an estimate of cell sodium activity (Table IX), one can calculate the direction of the sodium-calcium exchange by calculating the electrochemical potentials for each ion (~q2)…”

Section: Discussionmentioning

confidence: 99%

“…Our studies suggest that the stoichiometry is also 3 sodium:calcium. 3 Using the value of 3 as the stoichiometry, the open-circuit electrical measurements of Narvarte and Finn (35), the cell calcium activity obtained by Lee (25,26) and an estimate of cell sodium activity (Table IX) Hence, the driving force for the exchange is 3 A~Na --~Ca. Table IX shows that, when mucosal sodium is low, the exchanger operates in a calcium out, sodium in mode; when mucosal sodium is high, calcium moves in and sodium out.…”

Section: ~ + A23t87mentioning

confidence: 99%

Regulation of the sodium permeability of the luminal border of toad bladder by intracellular sodium and calcium: role of sodium-calcium exchange in the basolateral membrane.

Chase¹,

Al‐Awqati²

1981

The Journal of General Physiology

108

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Sodium movement across the luminal membrane of the toad bladder is the rate-limiting step for active transepitheliaI transport. Recent studies suggest that changes in intracellular sodium regulate the Na permeability of the luminal border, either directly or indirectly via increases in cell calcium induced by the high intracellular sodium. To test these proposals, we measured Na movement across the luminal membrane (the Na influx) and found that it is reduced when intracellular Na is increased by ouabain or by removal of external potassium. Removal of serosal sodium also reduced the influx, suggesting that the Na gradient across the serosal border rather than the cell Na concentration is the critical factor. Because in tissues such as muscle and nerve a steep transmembrane sodium gradient is necessary to maintain low cytosolic calcium, it is possible that a reduction in the sodium gradient in the toad bladder reduces luminal permeability by increasing the cell calcium activity. We found that the inhibition of the influx by ouabain or low serosal Na was prevented, in part, by removal of serosal calcium. To test for the existence of a sodium-calcium exchanger, we studied calcium transport in isolated basolateral membrane vesicles and found that calcium uptake was proportional to the outward directed sodium gradient. Uptake was not the result of a sodium diffusion potential. Calcium efflux from preloaded vesicles was accelerated by an inward directed sodium gradient. Preliminary kinetic analysis showed that the sodium gradient changes the Vm, x but not the Km of calcium transport. These results suggest that the effect of intracellular sodium on the luminal sodium.permeability is due to changes in intracellular calcium.

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INHIBITION OF FLUID REABSORPTION AND SODIUM EFFLUX BY LOW PERITUBULAR Na AND BY A23187 OR QUINIDINE IN ISOLATED PERFUSED PROXIMAL TUBULES OF THE RABBIT

Figueiredo

Friedman

Maack

et al. 1981

Kidney and Body Fluids

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CYTOSOLIC Ca ION ACTIVITY IN PROXIMAL TUBULAR CELLS OF NECTURUS KIDNEY

Cited by 3 publications

References 4 publications

Calcium reduces the sodium permeability of luminal membrane vesicles from toad bladder. Studies using a fast-reaction apparatus.

Calcium reduces the sodium permeability of luminal membrane vesicles from toad bladder. Studies using a fast-reaction apparatus.

Regulation of the sodium permeability of the luminal border of toad bladder by intracellular sodium and calcium: role of sodium-calcium exchange in the basolateral membrane.

INHIBITION OF FLUID REABSORPTION AND SODIUM EFFLUX BY LOW PERITUBULAR Na AND BY A23187 OR QUINIDINE IN ISOLATED PERFUSED PROXIMAL TUBULES OF THE RABBIT

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