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

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. 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 8644 (100 nM), and an L-type calcium channel blocker, nicardipine (1 microM). 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 microM) under the hypotonic condition. PTK inhibitors such as herbimycin A (30 nM), genistein (10 microM), and lavendustin A (10 microM) 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 microM) 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 microM), a PTP inhibitor, increased I(Ba) under both conditions. 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.