Mechanism of bicarbonate exit across basolateral membrane of the rabbit proximal convoluted tubule

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Abstract
To clarify the mechanism(s) of HCO-3 movement across the basolateral membrane, rabbit proximal convoluted tubules were perfused in vitro. Two possible mechanisms were examined: neutral HCO-3 exit coupled to chloride and rheogenic HCO-3 exit. A complete C1- substitution with isethionate in the lumen and bath did not affect HCO-3 reabsorption, suggesting that HCO-3 exit is not coupled to chloride. Addition of 2 mM Ba2+ to the bath, which has been shown to depolarize the basolateral membrane potential difference, caused a 42% inhibition of HCO-3 reabsorption and a 32% inhibition of volume flux, suggesting that HCO-3 exit is rheogenic. Ba2+ did not affect the volume flux when HCO-3 reabsorption was inhibited by acetazolamide, suggesting that the Ba2+ effect is not due to a general inhibition of cell metabolism. From these data we propose that HCO-3 exits the basolateral membrane by a rheogenic, chloride-independent mechanism.

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