Uncoupling of Na+H+ from Cl?HCO 3 ? exchange under some steady state conditions in rabbit gallbladder

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Abstract
The transapical Cl− influx and transepithelial Na+ transport were measured in rabbit gallbladder. Only 11.7% of the transported Na+ was found to be accompanied by HCO 3 − . 10−4 M SITS eliminated the HCO 3 − dependent fraction of Cl− influx (50%) but did not significantly alter intracellular Na+ activity and Na+ transport. Exposure to HCO3-free salines or to 10−4 M acetazolamide about halved Cl− influx and Na+ transport. 25 mM SCN− reduced Cl− influx to zero, decreased intracellular Na+ activity, but only halved Na+ transport which under these conditions was abolished only in the absence of HCO 3 − . Exposure to a Cl−-free saline produced effects similar to those caused by SCN−. These resuits suggest that when Cl−/HCO 3 − exchange is inhibited at the apical membrane, Na+/H+ exchange and transepithelial Na+ transfer are unmodified if HCO 3 − is available for transport. The permanent uncoupling of the exchangers and the elevated transepithelial transport of Na+ are not due to an increased activity of the parallel Na+−Cl− cotransport but to a redirection of HCO 3 − flux toward the basolateral side.