Atrial Natriuretic Factor Stimulates Phosphorylation of a 52-kDa Calmodulin-Binding Protein in Vascular Smooth Muscle Cells

The effect of atrial natriuretic factor (ANF) on the phosphorylation of the calmodulin-binding protein in vascular smooth muscle cells was investigated. Several phosphorylated calmodulin-binding proteins ranging in molecular weight from 205,000 to 50,000 were detected. Among them, we have found that the phosphorylation of a 52-kDa protein present mainly in the cytosolic fraction is stimulated by ANF and that the elevation of the phosphorylation is both time- and dose-dependent. Furthermore, the stimulation was mimicked by 8-bromo-cyclic GMP but not by 8-bromo-cyclic AMP. Endothelin induced significant inhibition of the phosphorylation. These results indicate that 52-kDa protein phosphorylation may be responsible for the regulation of vascular smooth muscle tone.