Evidence for rheogenic sodium bicarbonate cotransport in the basolateral membrane of oxyntic cells of frog gastric fundus

Ionic conductance properties of the basolateral cell membrane of oxyntic cells were studied in frog gastric fundus in vitro. After mounting the fundus in a modified Ussing chamber the serosal connective tissue was dissected off and individual oxyntic cells were punctured from the serosal surface with microelectrodes. Under resting conditions the membrane potential averaged −56.9, SD±9.5 mV (n=63), cytoplasm negative. Lowering or raising serosal HCO ⁻₃ concentration from 17.8 to 6 or 36 mmol/l respectively at constant\(p_{CO_2 } \) depolarized or hyperpolarized the cell membrane by +16.7 or −18.2 mV respectively. Sudden removal of serosal Na⁺ also depolarized the cell membrane (anomalous Nernst response). Since both the HCO ⁻₃ dependent and the Na⁺ dependent potential changes were strongly depressed by the disulfonic stilbene SITS and since the potential response to HCO ⁻₃ was virtually abolished in Na⁺-free solution we conclude that a rheogenic Na⁺ (HCO ⁻₃ ) _n -cotransport system (n>1) is present in the basolateral cell membrane of oxyntic cells. Its possible role in base transfer during HCl-secretion or HCO ⁻₃ secretion remains to be elucidated.