VASCULAR SMOOTH-MUSCLE CELLS GROWN ON MATRIGEL - A MODEL OF THE CONTRACTILE PHENOTYPE WITH DECREASED ACTIVATION OF MITOGEN-ACTIVATED PROTEIN-KINASE

Vascular smooth muscle cells have been shown to exist in two phenotypi c states which have been designated proliferative and contractile. The properties of rat aortic vascular smooth muscle cells grown on Matrig el were compared with cells grown on untreated plastic culture dishes. Cells grown on Matrigel manifested at least four important properties characteristic of the contractile phenotype as compared with cells gr own on plastic. The cells grown on Matrigel had altered morphology sim ilar to in vivo studies of contractile vascular smooth muscle. The cel ls had a low proliferative index, showed enhanced levels of the smooth muscle isoform of alpha-actin, and had an enhanced contractile respon se to the vasoconstrictor arginine vasopressin. All of these changes w ere maintained through at least five passages and could be reversed by replating cells grown on Matrigel back to uncoated plastic dishes. Ch anges in post-receptor signaling pathways which could account for the altered physiologic responses of the cells were investigated. Cells gr own on Matrigel showed no alterations in agonist-induced mobilization of intracellular Ca2+ or agonist-stimulated cAMP levels. However, stim ulation of mitogen activated protein kinase (MAP kinase) by both vasoc onstrictors and growth factors was inhibited by 50% in cells grown on Matrigel as compared with plastic. This decrease in agonist-induced MA P kinase was associated with a decrease in the levels of both p42 and p44 MAP kinase protein and a decrease in tyrosine phosphorylation of b oth isoforms in cells grown on Matrigel. Alterations in MAP kinase act ivation can account at least in part for the observed physiologic resp onses of contractile vascular smooth muscle. Growth of vascular smooth muscle cells on Matrigel represents a useful model to examine phenoty pic-dependent alterations in post-receptor signaling.