Phosphorylation events associated with cyclic nucleotide-dependent inhibition of smooth muscle contraction

Activation of cyclic nucleotide-dependent signaling pathways leads to relax ation of bovine carotid artery smooth muscle contractions and is associated with increased phosphorylation of the small heat shock-related protein (HS P20). Previous reports have shown that human umbilical artery smooth muscle is uniquely resistant to cyclic nucleotide-dependent relaxation, and HSP20 is not phosphorylated. In this investigation, we determined the phosphoryl ation events associated with cyclic nucleotide-dependent inhibition of smoo th muscle contraction. In carotid artery, activation of cyclic nucleotide-d ependent signaling pathways inhibited contractile responses to serotonin bu t did not inhibit myosin light chain phosphorylation or oxygen consumption. The inhibition of contraction was associated with increases in HSP20 phosp horylation. In umbilical artery, activation of cyclic nucleotide-dependent signaling pathways did not inhibit serotonin-induced contraction or myosin light chain phosphorylation. The lack of contractile inhibition in umbilica l artery was not associated with significant increases in HSP20 phosphoryla tion. In conclusion, cyclic nucleotide-dependent contractile inhibition is independent of the inhibition of myosin light chain phosphorylation or oxyg en consumption but does correlate with increased HSP20 phosphorylation.