Endothelin increases myofilament Ca2+ sensitivity in alpha-toxin-permeabilized rabbit mesenteric artery

Area of Science:

• Vascular Physiology
• Molecular Pharmacology

Background:

• Endothelin-1 (ET-1) is a potent vasoconstrictor.
• The precise mechanisms underlying ET-1-induced vascular smooth muscle contraction are not fully elucidated.
• Investigating ET-1's role in smooth muscle requires controlled experimental conditions.

Purpose of the Study:

• To investigate the mechanism of endothelin-1 (ET-1) contractions in Staphylococcus alpha-toxin-permeabilized vascular smooth muscle.
• To determine the role of G proteins and protein kinase C in ET-1-mediated vascular smooth muscle contraction.
• To elucidate the relationship between myosin light chain phosphorylation and contractile force.

Main Methods:

• Utilized alpha-toxin-permeabilized rabbit small mesenteric arteries.
• Measured isometric and isotonic force generation.
• Determined myosin light chain (MLC) phosphorylation levels.
• Assessed the effects of ET-1, GTP, GDP beta S, cAMP, cGMP, staurosporine, and chelerythrine.

Main Results:

• ET-1 plus GTP significantly enhanced myofilament Ca2+ sensitivity compared to Ca2+ alone, an effect reversed by GDP beta S.
• ET-1-induced contractions were relaxed by cAMP or cGMP.
• Inhibition of protein kinase C (PKC) relaxed ET-1 plus GTP-induced contractions.
• ET-1 plus GTP enhanced MLC phosphorylation but not shortening velocity, suggesting PKC activation over MLC kinase.

Conclusions:

• ET-1 increases myofilament Ca2+ sensitivity through a G protein-dependent pathway.
• Subsequent activation of protein kinase C plays a crucial role in ET-1-mediated vascular smooth muscle contraction.
• The study highlights a distinct signaling cascade for ET-1 compared to Ca2+-dependent mechanisms.