Myosin light chain and caldesmon phosphorylation in arterial muscle stimulated with endothelin-1

Endothelin-1 contracts porcine carotid arterial smooth muscle with an ED₅₀ of 10 nm. Contraction is associated with phosphorylation of the 20 000 dalton-regulatory light chain subunits of vascular myosin. Phosphopeptide mapping of light chains isolated from ³²PO₄-loaded muscle strips stimulated by endothelin-1 (5 × 10^-8 m) and comparison with maps generated from light chains phosphorylated in vitro or muscles stimulated with KCl (110 mm) or angiotensin-II (5 × 10^-8 m) indicates that Ca²⁺-calmodulin activation of myosin light chain kinase is a biochemical pathway stimulated by all three agonists. However, a small amount of phosphate (17%) was detected in a light chain peptide phosphorylated by protein kinase C. Endothelin-1 also stimulated phosphorylation of the thin filament protein, caldesmon, (from 0.35 mol PO₄/mol caldesmon to 0.52 mol PO₄/mol). Collectively, these results provide evidence that the effects of endothelin-1 on force generation and maintenance in vascular muscle may be dependent upon myosin light chain phosphorylation by Ca²⁺ calmodulin-requiring myosin light chain kinase and upon a thin filament mechanism that is modulated by phosphorylation of caldesmon.