Adenosine dephosphorylates myosin light chain in primary cultures of vascular smooth muscle cells from normotensive and spontaneously hypertensive rats

Objective: The aim was to determine whether vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) respond differently to adenosine than those from normotensive Wistar-Kyoto (WKY) rats. Design: Confluent primary cultures of VSMC derived from SHR and WKY aorta and mesenteric arteries and cerebral arteries were used. The effect of adenosine upon cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) formation and the phosphorylation of myosin light chain (MLC) was studied. Methods: MLC phosphorylation was estimated by subjecting VSMC extracts incubated with³²P to gel electrophoresis, followed by autoradiography and laser densitometry. cAMP and cCMP levels were measured by radioimmunoassay. Results: Baseline MLC phosphorylation levels were not significantly different in SHR and WKY VSMC. Adenosine caused dephosphorylation of MLC in a time- and dose-dependent manner. A maximal response of approximately 40% below control values was observed 5 min after addition of 10⁻⁵mol/l adenosine in SHR and WKY VSMC with no significant difference between the two strains. The maximally effective concentration of 10⁻⁵mol/l adenosine evoked increases in both cAMP and cGMP in VSMC from SHR and WKY rats to the same degree. Conclusion: We conclude that the overall ability of VSMC to relax, as evidenced by a marked decrease in MLC phosphorylation in response to adenosine, is unaltered in SHR.