ANGIOTENSIN-II INDUCED PHOSPHORYLATION OF MYOSIN LIGHT CHAIN IN VASCULAR SMOOTH-MUSCLE CELLS FROM SPONTANEOUSLY HYPERTENSIVE AND NORMOTENSIVE RATS

Study objective - The aim was to determine the changes in the phosphorylation of myosin light chain induced by angiotensin II in cultured vascular smooth muscle cells derived from normotensive (WKY) and spontaneously hypertensive rats (SHR). Design - Extracts of vascular smooth muscle cells incubated with [P-32]orthophosphoric acid were subjected to 4M urea-SDS electrophoresis, followed by autoradiography and laser densitometry. Experimental material - Confluent primary cultures of vascular smooth muscle cells from aorta, superior mesenteric arteries and cerebral arteries were used. Measurements and main results - The basal myosin light chain phosphorylation of SHR did not differ significantly from that of WKY. Stimulation with 1 nM angiotensin II increased incorporation of P-32 into the myosin light chain, which peaked at 4 min and then slowly declined until 15 min. Exposure to angiotensin II (0.001-10 nM) for 4 min evoked a dose dependent increase in the phosphorylation of myosin light chain with a maximal response 40-45% above basal values. No significant differences in the response to angiotensin II were detected between cells derived from the two strains. Saralasin, a specific angiotensin II antagonist, did not affect the basal phosphorylation of myosin light chain but completely abolished the effect of angiotensin II. Conclusions - Angiotensin II enhances the phosphorylation of the myosin light chain from vascular smooth muscle cells in aorta, mesenteric arteries, and cerebral arteries, but there are no differences in response between SHR and WKY.