Role of actin microfilament in osmotic stretch-induced increase of voltage-operated calcium channel current in guinea-pig gastric myocytes.

Using the whole-cell patch clamp technique, the role of actin microfilament in hyposmotic increase of voltage-operated calcium channel current (IBa) was studied in guinea-pig gastric myocytes. Hyposmotic superfusate (212 mOsm) increased peak IBa amplitude by 32.7 +/- 6.5%; when cytochalasin-D (Cyt-D, 20 microM), an actin cytoskeleton disruptor, was used, an increase of only 9.7 +/- 3.1% was seen. IBa response to osmotic stress was potentiated (45.1 +/- 4.1% increase) by 20 microM phalloidin, an actin microfilament stabilizer. However, colchicine (100 microM), an microtubule cytoskeleton disruptor, had no effect on either IBa or its response to hyposmotic solution. Phalloidin also induced a rightward shift of the I/V relationship of IBa, while Cyt-D itself had no effect. These results suggest that actin cytoskeleton may mediate hyposmotic stretch-induced IBa increase in gastric smooth muscle.