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 inhibi ting 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 ce ll voltage clamp technique, intracellular application of the tyrosine phosphatase inhibitors, sodium orthovanadate (100 mu M) and peroxyvana date (100 mu M orthovanadate + 1 mM H2O2) increased voltage-operated c alcium channel currents by 56% and 83%, respectively. 3 Bath applicati on of two other membrane permeant tyrosine phosphatase inhibitors, phe nylarsine oxide (100 mu M) and dephostatin (50 mu M) also increased vo ltage-operated calcium channel currents by 48% and 52%, respectively. 4 The selective tyrosine kinase inhibitor, tyrphostin-23 (100 mu M) re duced calcium channel currents by 41%. Pre-incubation with tyrphostin- 23 abolished the effects of peroxyvanadate, phenylarsine oxide and dep hostatin on calcium channels. 5 Western blot analysis of rabbit ear ar tery 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 o f tyrosine phosphatases increase voltage-operated calcium channel curr ents in arterial smooth muscle cells presumably due to increased tyros ine phosphorylation.