Effect of inhibition of tyrosine phosphatases on voltage-operated calcium channel currents in rabbit isolated ear artery cells

1 The effect of increasing cellular tyrosine phosphorylation by inhibiting endogenous tyrosine phosphatases was examined on voltage-operated calcium channel currents in vascular smooth muscle cells. 2 In single ear artery smooth muscle cells of the rabbit, studied by the whole cell voltage clamp technique, intracellular application of the tyrosine phosphatase inhibitors, sodium orthovanadate (100 mu M) and peroxyvanadate (100 mu M orthovanadate + 1 mM H2O2) increased voltage-operated calcium channel currents by 56% and 83%, respectively. 3 Bath application of two other membrane permeant tyrosine phosphatase inhibitors, phenylarsine oxide (100 mu M) and dephostatin (50 mu M) also increased voltage-operated calcium channel currents by 48% and 52%, respectively. 4 The selective tyrosine kinase inhibitor, tyrphostin-23 (100 mu M) reduced calcium channel currents by 41%. Pre-incubation with tyrphostin-23 abolished the effects of peroxyvanadate, phenylarsine oxide and dephostatin on calcium channels. 5 Western blot analysis of rabbit ear artery cell lysates showed increased tyrosine phosphorylation of several endogenous proteins following treatment with peroxyvanadate. 6 These results indicate that a number of structurally dissimilar inhibitors of tyrosine phosphatases increase voltage-operated calcium channel currents in arterial smooth muscle cells presumably due to increased tyrosine phosphorylation.