CELLULAR MECHANISMS OF CYCLIC NUCLEOTIDE-INDUCED VASORELAXATION

Purpose: Endothelial-derived vasorelaxants such as prostacyclin and ni tric oxide (NO) induce vascular smooth muscle relaxation through activ ation of cyclic nucleotide-dependent cellular signaling pathways. Howe ver, the specific events that lead to dissociation of actin and myosin and relaxation are not known. The purpose of this investigation was t o determine the late phase signaling events that modulate vascular smo oth muscle relaxation. Methods: Fresh bovine carotid artery smooth mus cle (BCASM) contractile responses were determined in a muscle bath und er Ca2+-containing and Ca2+-free conditions. Physiologic responses wer e correlated with phosphorylation events using whole cell phosphorylat ion and two-dimensional gel electrophoresis. Results: Cyclic nucleotid e-dependent vasorelaxation can occur without detectable changes in int racellular Ca2+ concentrations. However, vascular smooth muscles that had been precontracted with the phosphatase inhibitor calyculin were r efractory to relaxation. Vascular smooth muscle relaxation was associa ted with an increase in the phosphorylation of two 20 kDa proteins und er Ca2+-containing and Ca2+-free conditions. Conclusions: These result s suggest that Ca2+-independent mechanisms may also modulate vascular smooth muscle relaxation. Two possible late phase signaling mechanisms include phosphatase activation and an increase in the phosphorylation of two 20 kDa phosphoproteins.