Transport properties of the basolateral membrane of the oxyntic cells in frog fundic gastric mucosa.

The conductive properties of the basolateral membrane of oxyntic cells (OC) of frog fundic gastric mucosa were investigated by utilizing the microelectrode technique. By examining the response of the basolateral cell membrane potential difference, Vcs, to sudden ion concentration changes in the serosal bath it was concluded that the basolateral membrane of OC has a high Ba2+-sensitive K+-conductance, and no Cl- -conductance both in resting (cimetidine) and in stimulated (histamine) state. The response of Vcs to serosal Cl- -removal, consisting in a slight hyperpolarization (anomalous Nernst response), could not be explained by possible permeability changes to K+ and Na+ since the potential response to Cl- was essentially preserved by blocking K+-permeability with Ba2+ and replacing all Na+ by choline. Conversely, hyperpolarization of Vcs after Cl- -free perfusion was abolished by exposure to HCO3- -free solution, indicating that HCO3- -ions are required at the serosal bath for Cl- to get his effect. It was investigated wether the effect of Cl- was due to an electrogenic Na+ (HCO3-)n/Cl- exchange mechanism on the basolateral membrane. Experiments showed that the potential response to HCO3- -removal and to Na+-removal, consisting in a depolarization of Vcs, was similar both in presence and in absence of Cl-. Furosemide (0.5 mmol/l) had no effect on steady Vcs and Vt. The electrophysiological analysis of the data led to excluding the involvement of Na-Cl, Na-2Cl and NaK-2Cl cotransports, and to including the existence of an electrogenic Na+(HCO3-)n/Cl- exchange process, while suggests the presence of an electroneutral Cl-/HCO3- exchange mechanism to explain Cl- -transport across the basolateral membrane of OC.