The effect of membrane stretch on voltage-activated Ba2+ current (IBa) was studied in antral circular myocytes of guinea-pig using the whole- cell patch-clamp technique. The changes in cell volume were elicited by superfusing the myocytes with anisosmotic solutions. Hyposmotic superfusate (202 mosmol/l) induced cell swelling and increased peak values of IBa at 0 mV (from -406.6 +/- 45.5 pA to -547.5 +/- 65.6 pA, mean +/- SEM, n = 8) and hyperosmotic superfusate (350 mosmol/l) induced cell shrinkage and decreased peak values of IBa at 0 mV (to -269.5 +/- 39.1 pA, n = 8). Such changes were reversible and the extent of change was dependent on the osmolarity of superfusate. The values of normalized IBa at 0 mV were 1.43 +/- 0.04, 1.30 +/- 0.06, 1.23 +/- 0.04, 1.19 +/- 0.04, 1 and 0. 68 +/- 0.06 at 202, 220, 245, 267, 290 and 350 mosmol/l, respectively (n = 8). IBa was almost completely blocked by nicardipine (5 microM) under hyposmotic conditions. The values of steady-state half-inactivation voltage (-37.7 +/- 3.3 and -36.5 +/- 2.6 mV, under control and hyposmotic conditions, respectively) or the half-activation voltage (-13.6 +/- 2.3 and -13.9 +/- 1.9 mV) of IBa were not significantly changed (P > 0.05, n = 6). Cell membrane capacitance was slightly increased from 50.00 +/- 2.86 pF to 50.22 +/- 2.82 pF by a hyposmotic superfusate (P < 0.05, n = 6). It is suggested that cell swelling increases voltage-operated L-type calcium channel current and that such a property is related to the response of gastric smooth muscle to mechanical stimuli.