ISSN:
1432-1424
Keywords:
bicarbonate
;
Necturus
;
proximal tubule
;
basolateral membrane
;
electrical properties
;
transference numbers
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary The effects of stepwise concentration changes of K+ and HCO 3 − in the basolateral solution on the basolateral membrane potential (V bl) of proximal tubule cells of the doubly-perfusedNecturus kidney were examined using conventional microelectrodes. Apparent transference numbers were calculated from changes inV bl after alterations in external K+ concentration from 1.0 to 2.5mm (t K, 1.0–2.5), 2.5 to 10, and in external HCO 3 − concentration (at constant pH) from 5 to 10mm (t HCO3, 5–10), 10 to 20, or 10 to 50.t K, 2.5–10 was 0.38±0.02 under control conditions but was sharply reduced to 0.08±0.03 (P〉0.001) by 4mm Ba++. This concentration of Ba++ reducedV bl by 9±1 mV (at 2.5 external K+). Perfusion with SITS (5×10−4 m) for 1 hr hyperpolarizedV bl by 10±3 mV and increasedt K, 2.5–10 significantly to 0.52±0.01 (P〈0.001). Ba++ application in the presence of SITS depolarizedV bl by 22±3 mV. In control conditionst HCO3, 10–50 was 0.63±0.05 and was increased to 0.89±0.07 (P〈0.01) by Ba++ but was decreased to 0.14±0.02 (P〈0.001) by SITS. In the absence of apical and basolateral chloride, the response ofV bl to bicarbonate was diminished but still present (t HCO3, 10–20 was 0.35±0.03). Intracellular pH, measured with liquid ion-exchange microelectrodes, increased from 7.42±0.19 to 7.57±0.17 (P〈0.02) when basolateral bicarbonate was increased from 10 to 20mm at constant pH. These data show that the effects of bicarbonate onV bl are largely independent of effects on the K+ conductance and that there is a significant current-carrying bicarbonate pathway in the basolateral membrane. Hence, both K+ and HCO 3 − gradients are important in the generation ofV bl, and their relative effects vary reciprocally.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01872118
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