Activation of tyrosine kinase pathway by vanadate in gallbladder smooth muscle

Vanadate, an inhibitor of tyrosine phosphatase activity, might induce gallb ladder contraction through the stimulation of the tyrosine kinase pathway. The aim of this study was to characterize the effects of vanadate in the gu inea pig gallbladder smooth muscle. Vanadate exerts contractile effects whi ch are not mediated by neurotransmitter release. The tyrosine kinase inhibi tor genistein nearly abolished vanadate contraction, suggesting that an inc rease in protein tyrosine phosphorylation mediates the actions of vanadate. This suggestion was confirmed by Western blot analysis. Vanadate contracti ons were reduced in the presence of methoxyverapamil or in Ca2 + -free medi um, suggesting that vanadate may induce Ca2 + influx. Neither inactivation of the Na (+) /K (+) pump nor reversal of the Na (+) /Ca2 + exchanger can a ccount for vanadate's actions. Vanadate contractile effects were reduced by indomethacin, as well as mepacrine, the inhibitor of phospholipase A(2), b ut were not affected by phospholipase C inhibitors. Neither inhibitors of d iacylglycerol lipase nor protein kinase C reduced the response induced by v anadate. These data indicate that the effects of vanadate on smooth muscle are mainly mediated by protein tyrosine phosphorylation and reveal a new li nk between tyrosine phosphorylation and arachidonic acid metabolism in the control of gallbladder smooth muscle contraction. (C) 2000 Elsevier Science Inc.