Electrophysiological investigation of microdissected gastric glands of bullfrog I. Basolateral membrane properties in the resting state

In the present experiments we have made a new attempt to characterize the ion transport properties of H+-secreting cells of the gastric mucosa using electrophysiological techniques. Individual gastric glands of bullfrog fundus mucosa were manually dissected, mounted in holding pipettes and superfused with various test solutions while individual cells were punctured with conventional or H+-sensitive double-barrelled microelectrodes. All measurements were performed in the resting state (0.1 mmol/l cimetidine). In HCO3− containing control Ringer solution the cell membrane potential (Vb) averaged −45.6±0.9 mV (±SEM, n=54). From the fast initial Vb responses to changing bath K+, Na+, Cl− or HCO3− concentrations we deduced that the basolateral cell membrane contains conductances for K+, Na+, and Cl− but not for HCO3−, and that a Na+-HCO3− cotransporter is not present. The K+ conductance was inhibited by Ba2+ (3 mmol/l), but the Cl− conductance was not inhibited by 4,4′ diisothiocyanato-stilbene-2,2′disulphonic acid (DIDS, 0.3 mmol/l), nor selectively inhibited by 5-nitro-2-(3)-phenylpropyl-aminobenzoate (NPPB, 10 (μmol/l). In a great number of cells the Vb response to Cl− substitution revealed two components: an initial spiking depolarization which reflected conductive Cl− efflux and a secondary slow hyperpolarization, the origin of which was not immediately evident. Since the latter response could be mimicked by CO2-free perfusion, strongly depressed by Ba2+ and eliminated by DIDS, we conclude that it reflects HCO3− uptake into the cells via a DIDS sensitive Cl−/HCO3− exchanger which alkalinizes the cells and stimulates the basolateral K+ conductance. Our results confirm, revise and extend the results of previous, less direct, investigations of gastric cell ion transport