Acid secretion, resistance, short-circuit current, and voltage-clamping in frog's stomach

Abstract

Certain findings seemed to invalidate the author's separate site theory of HCl formation (separate H+ and Cl– ion electrogenic mechanisms). These findings are analyzed and further pertinent experimental data on the frog's stomach are presented. With an in vitro chamber method it was found that the onset of secretion (histamine stimulation) resulted in a sustained decrease in transmucosal resistance and a small initial increase in potential difference (PD) followed by a larger decrease. The ratio PD/resistance (the predicted short-circuit current, Isc) initially increased and then decreased. During short-circuiting, the onset of secretion resulted in the predicted changes in Isc. Following the establishment of secretion, changes in the H+ ion secretory rate frequently occurred without significant changes in Isc. Thiocyanate inhibition resulted in a transient increase in Isc and a sustained increase in both the PD and resistance. Clamping of the voltage across the mucosa at negative levels (nutrient negative) reversibly decreased the H+ ion rate. The average voltage necessary to reduce the H+ ion rate to zero was –140 mv. With a single loop equivalent circuit the average EMF of the H+ ion mechanism on the basis of the voltage-clamping experiments is 140 mv. Findings are explained by the separate site theory with the assumption of cytoplasmic biochemical coupling.