REGULATION OF THE EXPRESSION OF CYCLIC GMP-DEPENDENT PROTEIN-KINASE BY CELL-DENSITY IN VASCULAR SMOOTH-MUSCLE CELLS

Cyclic GMP-dependent protein kinase (cGMP kinase) is the major recepto r protein for cGMP in vascular smooth muscle. Vascular smooth muscle c ells (VSMC) isolated from the rat aorta express type I cGMP kinase at high levels, but expression decreases markedly upon passage of the cel ls. In primary or early passage, the expression of cGMP kinase is lowe st when cells are plated at low density as assessed by immunological a nd Northern analyses. Expression increases at confluence and is mainta ined in postconfluent cultures. With repeated passaging, however, the levels of cGMP kinase decrease even in confluent and postconfluent cul tures so that after several passages enzyme levels are undetectable. T he decrease in expression in passaged cells is not due to exposure to serum-derived growth factors, but rather on the repeated exposure of c ells to conditions in which cell density is reduced (i.e., subculturin g). These results indicate that aortic VSMC grown at low density or th ose repetitively passaged have reduced expression of cGMP kinase, and thus may not represent appropriate cultures with which to investigate the role of nitric oxide and cGMP in VSMC function.