MASS ANALYSIS OF 1,2-DIACYLGLYCEROL IN CULTURED RABBIT VASCULAR SMOOTH-MUSCLE CELLS - COMPARISON OF STIMULATION BY ANGIOTENSIN-II AND ENDOTHELIN

We compared the effects of angiotensin II and endothelin on mass levels of 1,2-diacylglycerol, an endogenous activator of protein kinase C, in cultured rabbit vascular smooth muscle cells with the effects of these vasoconstrictors on contractile responses of rabbit aortic strips. At a high concentration (1 μM), both angiotensin II and endothelin induced a biphasic formation of 1,2-diacylglycerol with an early transient phase and a late sustained phase. At this high concentration, angiotensin II caused a transient contraction followed by a gradual relaxation, whereas endothelin caused a slowly developing and sustained contraction. At a low concentration (EC50 for the early phase of 1,2-diacylglycerol formation), angiotensin II also induced a biphasic formation of 1,2-diacylglycerol and caused a transient contraction, but endothelin induced a monophasic formation of 1,2-diacylglycerol with only an early peak. Despite a rapid decrease of 1,2-diacylglycerol, endothelin at this low concentration still caused a sustained contraction. At both the high and low concentrations, the 1,2-diacylglycerol level was sustained higher for angiotensin II, whereas the tension during the late tonic phase of contraction was greater for endothelin. These results suggest that the unique persistent nature of endothelin-induced contraction is not attributed simply to the stimulatory effect of this peptide on the 1,2-diacylglycerol/protein kinase C pathway.