Ethanol induces volume changes and gap junction closure via intracellular Ca2+ signalling pathway in cultured rabbit gastric epithelial cells

Abstract

Background: Ethanol is a well‐established ‘barrier breaker’ in gastric mucosa, but its effects at cellular level remain to be detailed. Methods: Gastric epithelial cells were isolated from rabbits and cultured to monolayers. Intracellular calcium was measured spectrofluorometrically with fura‐2. The patency of gap junctions was assessed by photobleaching a small area of 5‐carboxyfluorescein loaded monolayer and measuring recovery of fluorescence. For cell volume measurements the change in fluorescence intensity was followed in calcein‐loaded monolayers with a confocal microscope. Results: Intracellular calcium concentration was increased from 65 ± 9 to 140 ± 17 nM; recovery of fluorescence signal after photobleaching was diminished from 53% ± 11% to 9% ± 3%; and cell volume was decreased significantly after 10 min exposure to 5% (vol/vol) ethanol. This volume decrease was prevented with serosal application of the potassium channel blocker, quinine, or by blocking the intracellular calcium signalling pathway with the intracellular calcium‐chelating agent BAPTA. This suggests that luminal ethanol opens the basolateral calcium‐dependent potassium selective channels via calcium signalling pathway, with resultant shrinkage of the cell. Conclusion: Intracellular calcium concentration is increased, gap junctions are closed and cell volume is decreased after exposure to 5% ethanol. Since gap junctions are known to be calcium gated, it is likely that their closure is secondary to the elevated cytosolic calcium in ethanol injured cells. This may have a protective function by limiting intercellular spread of impending cell injury. The opening of the basolateral potassium channel probably underlies the ethanol‐induced cell shrinkage and might contribute to the ethanol‐provoked epithelial damage.