Anomalous potential difference responses to changes in sodium concentration in the antrum of frog stomach.

Previously, an electrogenic Na-Cl symport was found in the fundus, and the question arises of whether there is one in the antrum, a tissue that does not secrete acid. In an in vitro preparation of the antrum of Rana catesbeiana, we found that when the [Na+] in nutrient solution was decreased (choline for Na+) the transmucosal potential difference (PD) decreased (the positivity of nutrient side decreased), and when the [Na+] was increased the PD increased. These PD changes were anomalous for Na+ but not for choline. A linear relationship for PD versus log [Na+] and not versus log [choline] excluded a choline conductive pathway. The anomalous PD response was decreased but not abolished by 10(-3) M ouabain. Normal PD responses resulted from [Na+] changes in Cl--free (SO2-4) solutions. PD responses to changes in nutrient [Cl-] were normal but decreased in the absence of Na+. Data are compatible with a passive electrogenic Na-Cl symport with more chloride than sodium ions transported per cycle, as in the fundus. Symport conductance-to-total Cl- conductance ratio is higher in antrum than in the fundus. Data from the luminal side were compatible with apical membrane conductances for Na+ and Cl-.