Electrophysiological effects of cholinergic agonists in surface epithelium of Necturus gastric antrum

Intracellular microelectrode techniques were used to characterize voltage and conductance properties of the basolateral membrane of surface epithelial cells in in vitro Necturus antral mucosa. Flux studies confirmed that this tissue secretes HCO₃/^- under resting conditions and during response to cholinergic stimulation. In studies using intracellular microelectrodes, exposure to cholinergic agonists such as acetylcholine, bethanechol, or carbachol elicited an initial hyperpolarization followed by depolarization of the basolateral cell membrane associated with up to fourfold increases in basolateral membrane conductance. Effects of acetylcholine were dose dependent (10^-6-10^-4 M) and prevented by pretreatment of tissues with the nonselective muscarinic receptor blocker atropine. Some variation in this response to cholinergic stimulation was observed and appeared to be related to the season (fall/winter/early spring vs. late spring/summer). Despite such variability, circuit analysis and ion-substitution studies indicated that the carbachol-induced increases in basolateral conductance were due to increases in conductance to K⁺ and Cl^-. These increases in basolateral transport processes may serve to stabilize cell ion composition and membrane electrical properties during cholinergic stimulation of mucus and HCO₃/^- secretions.