Uncoupling of Na+H+ from Cl-HCO3- exchange under some steady state conditions in rabbit gallbladder

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 HCO3-. 10(-4) M SITS eliminated the HCO3- 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 HCO3-. Exposure to a Cl- -free saline produced effects similar to those caused by SCN-. These results suggest that when Cl-/HCO3- exchange is inhibited at the apical membrane, Na+/H+ exchange and transepithelial Na+ transfer are unmodified if HCO3- 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 HCO3- flux toward the basolateral side.