MODEL OF BICARBONATE SECRETION BY RESTING FROG STOMACH FUNDUS MUCOSA .2. ROLE OF THE OXYNTOPEPTIC CELLS

In the present publication we report mainly electrophysiological studi es on oxyntopeptic cells of frog gastric mucosa which aim at clarifyin g a possible involvement of these cells in the process of resting gast ric alkali (HCO3-) secretion, described in the preceding publication. The experiments were performed on intact gastric fundus mucosa of Rana esculenta mounted in Ussing chambers. After removal of the muscle, an d connective tissue layer oxyntopeptic cells were punctured from the s erosal surface with conventional or pH-sensitive microelectrodes to me asure, besides transepithelial voltage and resistance, the basolateral cell membrane potential, the voltage divider ratio, and the cell pH i n response to secretagogues and/or changes in serosal ion concentratio n. Carbachol (10(-4) mol/l), which transiently stimulated HCO3- secret ion by 0.22 mu mol.cm(-1).h(-1), transiently acidified the cells by 0. 09+/-SEM 0.03 pH units (n=6) and transiently induced an apical cell me mbrane anion conductance. According to the model of gastric HCO3- secr etion presented in the preceding publication, this anion conductance c ould be involved in gastric HCO3- secretion, mediating, besides Cl- ef flux, also apical HCO3- efflux. In addition carbachol stimulated basol ateral Na+(HCO3-)(n)-cotransport, which according to the results from the preceding publication mediates basolateral HCO3- uptake for secret ion. By contrast, cAMP-mediated secretagogues, such as histamine or ot hers, which stimulate HCl secretion and transiently alkalinize the oxy ntopeptic cells; were found to down-regulate the basolateral Na+(HCO3- )(n)-cotransporter. The data indicate that the oxyntopeptic cells may play a role in HCO3- secretion across resting frog fundus mucosa.