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 tyrosine phosphorylation and activation of p42 mitogen-activated protein (MAP) kinase (p42MAPK) in vascular smooth muscle cells (VSMC). In VSMC, 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 therefore 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 downregulation of PKC by PMA pretreatment abolished AVP- induced stimulation of p42MAPK. When [Ca²⁺](i) was elevated to the same level as with AVP, using either ionomycin (0.1 μM) or thapsigargin (0.1 μM), MAP kinase was only partially activated. Elevation of [Ca²⁺](i) to supraphysiological levels by 1 μM ionomycin stimulated MAP kinase activity to the same extent as AVP. This effect was blocked by downregulation of PKC. The intracellular Ca²⁺ chelator BAPTA [1,2-bis(2-aminophenoxy)ethane- N,N,N',N'-tetraacetic acid] blocked AVP-induced [Ca²⁺](i) increase but did not affect AVP stimulation of p42MAPK. Thus AVP-induced activation of p42MAPK requires only the activation of PKC but not an increase in [Ca²⁺](i).