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 x 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 x 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.

Abscisic acid enhances aggregation and fusion of phospholipid vesicles.

The plant hormone abscisic acid (ABA) is shown to enhance the aggregation and fusion of small unilamellar lipid vesicles composed of 80 mol% dimyristoylphosphatidylcholine (DMPC) and 20 mol% dimyristoylphosphatidylcholine (DMPE). Aggregation and fusion did not occur with single component (100 mol%) DMPC vesicles. Fusion was followed by two fundamentally different techniques, fluorescence resonance energy transfer which monitors intermixing of bilayers and ANTS-DPX which monitors intermixing of the sequestered aqueous interiors. It is suggested that a previously unreported role of ABA may be as a membrane fusagen.