Differential effects of a K+ channel agonist and Ca2+ antagonists on myosin light chain phosphorylation in relaxation of endothelin-1-contracted tracheal smooth muscle.
Smooth muscle contraction and relaxation are generally considered to be associated with phosphorylation and dephosphorylation of the 20-kDa regulatory myosin light chain (LC20). Thus, contractions of lamb tracheal smooth muscle induced by Bay K 8644 and relaxed by calcium channel blockers (verapamil, D-600 and nitrendipine) are accompanied by an increase and decrease, respectively, of LC20 phosphorylation. Similarly, endothelin-1 (ET-1) induces a sustained contraction, which is coupled with elevated LC20 phosphorylation and reversed by LC20 dephosphorylation after application of a potassium channel agonist (EMD 52692). In contrast, calcium channel blockers relax ET-1-induced contraction without any dephosphorylation of myosin light chains (MLC), suggesting that MLC phosphatase is inhibited in this case. Obviously, MLC dephosphorylation is not a prerequisite for smooth muscle relaxation. The variable relationship between MLC phosphorylation and force during relaxation suggests that there are mechanisms other than MLC phosphorylation that are important for regulation of contraction and relaxation in smooth muscle.
Katoch
S S
SS
Department of Biosciences, Himachal Pradesh University, Summer Hill, Shimla-171005, India.
Rüegg
J C
JC
Pfitzer
G
G
D000818:Animals; D001578:Benzopyrans / Q000494:pharmacology*; D004095:Dihydropyridines / Q000494:pharmacology*; D019332:Endothelin-1 / Q000494:pharmacology*; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D018994:Myosin Light Chains / Q000187:drug effects*; D009568:Nitrendipine / Q000494:pharmacology; D012756:Sheep; D014132:Trachea / Q000187:drug effects*; D014700:Verapamil / Q000494:pharmacology*
D001578:Benzopyrans; D004095:Dihydropyridines; D019332:Endothelin-1; D018994:Myosin Light Chains; C061050:bimakalim; D009568:Nitrendipine; D014700:Verapamil