Specific inhibition of stretch-induced increase in L-type calcium channel currents by herbimycin A in canine basilar arterial myocytes

1 The effects of protein-tyrosine kinase (PTK) and protein-tyrosine phosphatase (PTP) inhibitors on voltage-activated barium currents (I-Ba) through L-type calcium channels increased by hypotonic solution were investigated in canine basilar arterial myocytes by the whole-cell patch-clamp technique. 2 I-Ba was elicited by depolarizing step from a holding potential of - 80 to + 10 mV and identified by using an L-type calcium channel agonist, Bay K 8643 (100 nM), and an L-type calcium channel blocker, nicardipine (1 mu M). 3 Hypotonic superfusate induced cell swelling and acted as a stretch stimulus, which reversibly increased peak I-Ba amplitude at +10 mV. I-Ba was also decreased by nicardipine (1 mu M) under the hypotonic condition. 4 PTK inhibitors such as herbimycin A (30 nM), genistein (10 mu M), and lavendustin A (10 mu M) decreased I-Ba enhanced by hypotonic solution. Genistein also decreased I-Ba in a concentration-dependent manner under the isotonic condition. The inactive genistein analogue daidzein (10 mu M) had no effect on I-Ba under either the isotonic or hypotonic condition. By contrast, herbimycin A did not decrease I-Ba under the isotonic condition. Sodium orthovanadate (10 mu M), a PTP inhibitor, increased I-Ba under both conditions. 5 The present results suggest that cell swelling by hypotonic solution increases the L-type calcium channel currents in canine basilar artery and that herbimycin-sensitive PTK activity is primarily involved in the enhancement of calcium channel currents.