Endothelin-1, but not angiotensin II, induces afferent arteriolar myosin diphosphorylation as a potential contributor to prolonged vasoconstriction

Abstract

Bolus administration of endothelin-1 elicits long-lasting renal afferent arteriolar vasoconstriction, in contrast to transient constriction induced by angiotensin II. Vasoconstriction is generally evoked by myosin regulatory light chain (LC 20) phosphorylation at Ser19 by myosin light chain kinase (MLCK), which is enhanced by Rho-associated kinase (ROCK)-mediated inhibition of myosin light chain phosphatase (MLCP). LC 20 can be diphosphorylated at Ser19 and Thr18, resulting in reduced rates of dephosphorylation and relaxation. Here we tested whether LC 20 diphosphorylation contributes to sustained endothelin-1 but not transient angiotensin II-induced vasoconstriction. Endothelin-1 treatment of isolated arterioles elicited a concentration- and time-dependent increase in LC 20 diphosphorylation at Thr18 and Ser19. Inhibition of MLCK or ROCK reduced endothelin-1-evoked LC 20 mono- and diphosphorylation. Pretreatment with an ETB but not an ETA receptor antagonist abolished LC 20 diphosphorylation, and an ETB receptor agonist induced LC 20 diphosphorylation. In contrast, angiotensin II caused phosphorylation exclusively at Ser19. Thus, endothelin-1 and angiotensin II induce afferent arteriolar constriction via LC 20 phosphorylation at Ser19 due to calcium activation of MLCK and ROCK-mediated inhibition of MLCP. Endothelin-1, but not angiotensin II, induces phosphorylation of LC 20 at Thr18. This could contribute to the prolonged vasoconstrictor response to endothelin-1.