BACKGROUND Regulatory volume decrease (RVD) after osmotic cellular swelling has been shown in several gastrointestinal epithelia but not in esophageal cells. In acid reflux disease, esophageal injury may be related in part to loss of RVD. METHODS Isolated basal esophageal cells were exposed to an external hyposmolar solution, and changes in relative cell size were assessed using a Coulter counter (Hilaleah, FL) in the presence of K+ and Cl- transport inhibitors and at varying extracellular pH (pHo). RESULTS At pHo 7.4, a 30% hyposmotic dilution of the external solution caused an initial peak cell swelling (1.15 +/- 0.05-fold) followed by a return to starting cell size by 5 minutes (RVD). RVD was inhibited by Ba2+ (4 mmol/L), quinine (1 mmol/L), or increasing the [K+]o > or = 10 mmol/L. RVD was also inhibited by depleting [Cl-]i or in the presence of 0.5 mmol/L 4,4'-diisothiocyanastostilbene-2,2'-disulfonic acid disodium salt (DIDS) or 50 mumol/L diphenylamine-2-carboxylate, a Cl- conductance inhibitor. To test the effect of pH on RVD, cells in solutions at pHo 7.4, 7.0, or 6.8 were subjected to hyposmotic stress; RVD was significantly inhibited at pHo 6.8. This pH-dependent inhibition of RVD was reversed in the presence of valinomycin, a K+ ionophore. CONCLUSIONS These studies show that isolated esophageal cells possess RVD mechanisms that are mediated by Cl(-)- and pH-dependent K+ effluxes. RVD appears to be inhibited by a decrease in pHo, suggesting the possibility that acid-induced esophageal injury results from inhibition of normal volume regulatory mechanisms.