RECEPTOR-ACTIVATED INCREASES IN INTRACELLULAR CALCIUM AND PROTEIN-TYROSINE PHOSPHORYLATION IN VASCULAR SMOOTH-MUSCLE CELLS

We studied the effects of protein tyrosine kinase inhibitors (genistei n and tyrphostin) on receptor-activated increases in cellular Ca2+ ([C a2+](i)), and protein tyrosine phosphorylation in cultured canine femo ral 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 7 0-80% of the transient increase in [Ca2+](i) evoked by either agonist is due to influx of extracellular Ca2+ whereas the plateau phase is on ly due to Ca2+ entry, Pre-incubation with genistein or tyrphostin mark edly inhibited the transient rise in [Ca2+](i) evoked by serotonin or phenylephrine. Immunoblot analysis of cell extracts with antiphosphoty rosine antibodies revealed that serotonin and phenylephrine also evoke d an increase in tyrosine phosphorylation of several substrates. These increases were abolished by tyrosine kinase inhibitors, One of the ma jor substrates was recognized by an antibody for rasGAP. These data su ggest that receptor-activated increases in [Ca2+](i) in vascular smoot h muscle cells may be coupled to receptor-activated increases in prote in tyrosine phosphorylation.