K+ selectivity and HCl secretion in Xenopus and their relation to cAMP and Ba2+

Doses of 1, 5, and 10 mM adenosine 3',5'-cyclic monophosphate (cAMP) applied to previously resting Xenopus gastric mucosae initiated a dose-dependent acid secretory response. Increases in the K+ concentration of the submucosal solution. [K+sm], resulted in higher acid secretory rates and concomitant lower transmucosal resistances at the indicated cAMP concentration. The transmucosal potential difference, PD, had a liner slope against log [K+sm] over the range of 20-80 mM K+sm. Values of the slope (K+ selectivity, -PD/log[K+sm]) were less than 26 mV/log for resting mucosae, and in the range of 29-58 mV/log for both spontaneously secreting and cAMP-stimulated mucosae. These values were dose dependent on the cAmP concentration. In the presence of 10 mM Ba2+ together with cAMP, the K+ selectivity and the H+ secretory rate decreased compared with the case of cAMP only.