AVP-INDUCED ACTIVATION OF MAP KINASE IN VASCULAR SMOOTH-MUSCLE CELLS IS MEDIATED THROUGH PROTEIN-KINASE-C

Arginine vasopressin (AVP) has been shown to stimulate late tyrosine p hosphorylation and activation of p42 mitogen-activated activated prote in (MAP) kinase (p42MAPK) in vascular smooth muscle cells (VSMC). In V SMC, AVP increases free intracellular Ca2+ concentration ([Ca2+]i) and activates protein kinase C (PKC) through activation of phospholipase C. The contribution of PKC and [Ca2+]i in p42MAPK regulation was there fore determined. Activation of PKC by phorbol 12-myristate 13-acetate (PMA) stimulated tyrosine phosphorylation and activation of p42MAPK to the same extent as AVP. Inhibition of PKC by staurosporine or downreg ulation of PKC by PMA pretreatment abolished AVP-induced stimulation o f p42MAPK. When [Ca2+]i was elevated to the same level as with AVP, us ing either ionomycin (0.1 muM) or thapsigargin (0.1 muM), MAP kinase w as only partially activated. Elevation of [Ca2+]i to supraphysiologica l levels by 1 muM ionomycin stimulated MAP kinase activity to the same extent as AVP. This effect was blocked by downregulation of PKC. The intracellular Ca2+ chelator BAPTA ,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid) blocked AVP-induced [Ca2+], increase but did not, affect AVP stimulation of p42MAPK. Thus AVP-induced activation of p42 MAPK requires only the activation of PKC but not an increase in [Ca2+] i.