ELECTROPHYSIOLOGICAL INVESTIGATION OF MICRODISSECTED GASTRIC GLANDS OF BULLFROG .1. 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 muco sa using electrophysiological techniques. Individual gastric glands of bullfrog fundus mucosa were manually dissected, mounted in fielding p ipettes and superfused with various test solutions while individual ce lls 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 t he cell membrane potential (V-b) averaged -45.6+/-0.9 mV (+/-SEM, n=54 ). From the fast initial V-b responses to changing bath K+, Na+, Cl- o r HCO3- concentrations we deduced that the basolateral cell membrane c ontains conductances for K+, Na+, and Cl- but not for HCO3- and that a Na+-HCO3- cotransporter is not present. The K+ conductance was inhibi ted 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-aminobenzoat e (NPPB, 10 mu mol/l). In a great number of cells the V-b response to Cl- substitution revealed two components: an initial spiking depolariz ation which reflected conductive Cl- efflux and a secondary slow hyper polarization, the origin of which was not immediately evident. Since t he latter response could be mimicked by CO2-free perfusion, strongly d epressed by Ba2+ and eliminated by DIDS, we conclude that it reflects HCO3- uptake into the cells via a DIDS sensitive Cl-/HCO3- exchanger w hich alkalinizes the cells and stimulates the basolateral K+ conductan ce. Our results confirm, revise and extend the results of previous, le ss direct, investigations of gastric cell ion transport.