Receptor-activated increases in intracellular calcium and protein tyrosine phosphorylation in vascular smooth muscle cells

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Abstract
We studied the effects of protein tyrosine kinase inhibitors (genistein and tyrphostin) on receptor-activated increases in cellular Ca2+ ([Ca2+]i), and protein tyrosine phosphorylation in cultured canine femoral arterial smooth muscle cells. Fura-2 imaging analysis showed that each agonist evoked a transient increase in ([Ca2+]i) followed by a sustained plateau phase. Experiments in Ca2+-free medium showed that 70–80% of the transient increase in [Ca2+]i evoked by either agonist is due to influx of extracellular Ca2+ whereas the plateau phase is only due to Ca2+ entry. Pre-incubation with genistein or tyrphostin markedly inhibited the transient rise in [Ca2+]i evoked by serotonin or phenylephrine. Immunoblot analysis of cell extracts with antiphosphotyrosine antibodies revealed that serotonin and phenylephrine also evoked an increase in tyrosine phosphorylation of several substrates. These increases were abolished by tyrosine kinase inhibitors. One of the major substrates was recognized by an antibody for rasGAP. These data suggest that receptor-activated increases in [Ca2+]i in vascular smooth muscle cells may be coupled to receptor-activated increases in protein tyrosine phosphorylation