Electrophysiological investigation of microdissected gastric glands of bullfrog. II. Basolateral membrane properties in the presence of histamine

Agonist-induced cytoplasmic volume changes in cultured rabbit parietal cells

Concomitant Na(+)/H(+) and Cl(-)/HCO(3)(-) exchange activation occurs during stimulation of acid secretion in cultured rabbit parietal cells, possibly related to a necessity for volume regulation during the secretory process. We investigated whether cytoplasmic volume changes occur during secretagogue stimulation of cultured rabbit parietal cells. Cells were loaded with the fluorescent dye calcein, and the calcein concentration within a defined cytoplasmic volume was recorded by confocal microscopy. Forskolin at 10(-5) M, carbachol at 10(-4) M, and hyperosmolarity (400 mosmol) resulted in a rapid increase in the cytoplasmic dye concentration by 21 +/- 6, 9 +/- 4, and 23 +/- 5%, respectively, indicative of cell shrinkage, followed by recovery to baseline within several minutes, indicative of regulatory volume increase (RVI). Depolarization by 5 mM barium resulted in a decrease of the cytoplasmic dye concentration by 10 +/- 2%, indicative of cell swelling, with recovery within 15 min, and completely prevented forskolin- or carbachol-induced cytoplasmic shrinkage. Na(+)/H(+) exchange inhibitors slightly reduced the initial cell shrinkage and significantly slowed the RVI, whereas 100 microM bumetanide had no significant effect on either parameter. We conclude that acid secretagoguges induce a rapid loss of parietal cell cytoplasmic volume, followed by RVI, which is predominantly mediated by Na(+)/H(+) and Cl(-)/HCO(3)(-) exchange.

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 mumol/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.