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 microfil ament in hyposmotic increase of voltage-operated calcium channel curre nt (I-BR) was studied in guinea-pig gastric myocytes. Hyposmotic super fusate (212 mOsm) increased peak I-Ba amplitude by 32.7 +/- 6.5%; when cytochalasin-D (Cyt-D, 20 mu M), an actin cytoskeleton disruptor, was used, an increase of only 9.7 +/- 3.1% was seen, I-Ba response to osm otic stress was potentiated (45.1 +/- 4.1% increase) by 20 mu M phallo idin, an actin microfilament stabilizer, However, colchicine (100 mu M ): an microtubule cytoskeleton disrupter, had no effect on either I-Ba or its response to hyposmotic solution, Phalloidin also induced a rig htward shift of the I/V relationship of I-Ba, while Cyt-D itself had n o effect, These results suggest that actin cytoskeleton may mediate hy posmotic stretch-induced I-Ba increase in gastric smooth muscle.