EFFECT OF STRETCH ON CALCIUM-CHANNEL CURRENTS RECORDED FROM THE ANTRAL CIRCULAR MYOCYTES OF GUINEA-PIG STOMACH

The effect of membrane stretch on voltage-activated Ba2+ current (I-Ba ) was studied in antral circular myocytes of guinea-pig using the whol e-cell patch-clamp technique. The changes nicely volume were elicited by superfusing the myocytes with anisosmotic solutions. Hyposmotic sup erfusate (202 mosmol/l) induced cell swelling and increased peak value s of I-Ba 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 c ell shrinkage and decreased peak values of I-Ba at 0 mV (to -269.5 +/- 39.1 pA, n = 8). Such changes were reversible and the extent of chang e was dependent on the osmolarity of superfusate. The values of normal ized I-Ba 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 mo smol/l, respectively (n = 8). I-Ba was almost completely blocked by ni cardipine(5 mu M) under hyposmotic conditions. The values of steady-st ate half-inactivation voltage (-37.7 +/- 3.3 and -36.5 +/- 2.6 mV, und er control and hyposmotic conditions, respectively) or the half-activa tion voltage (-13.6 +/- 2.3 and -13.9 +/- 1.9 mV) of I-Ba were not sig nificantly changed (P > 0.05, n = 6). Cell membrane capacitance was sl ightly increased from 50.00 +/- 2.86 pF to 50.22 +/- 2.82 pF by a hypo smotic superfusate (P < 0.05, n = 6). It is suggested that cell swelli ng 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.