title: Evidence of a role for calmodulin in the regulation of calcium release from skeletal muscle sarcoplasmic reticulum.
abstract: The effect of calmodulin and calmodulin inhibitors on the "Ca2+ release channel" of "heavy" skeletal muscle sarcoplasmic reticulum (SR) vesicles was investigated. SR vesicles were passively loaded with 45Ca2+ in the presence of calmodulin and its inhibitors, followed by measurement of 45Ca2+ release rates by means of a rapid-quench-Millipore filtration method. Calmodulin at a concentration of 2-10 microM reduced 45Ca2+ efflux rates from passively loaded vesicles by a factor of 2-3 in media containing 10(-6)-10(-3) M Ca2+. At 10(-9) M Ca2+, calmodulin was without effect. 45Ca2+ release rates were varied 1000-fold (k1 approximately equal to 0.1-100 s-1) by using 10(-5) M Ca2+ with either Mg2+ or the ATP analogue adenosine 5'-(beta,gamma-methylenetriphosphate) in the release medium. In all instances, a similar 2-3-fold reduction in release rates was observed. At 10(-5) M Ca2+, 45Ca2+ release was half-maximally inhibited by about 2 X 10(-7) M calmodulin, and this inhibition was reversible. Heavy SR vesicle fractions contained 0.1-02 micrograms of endogenous calmodulin/mg of vesicle protein. However, the calmodulin inhibitors trifluoperazine, calmidazolium, and compound 48/80 were without significant effect on 45Ca2+ release at concentrations which inhibit calmodulin-mediated reactions in other systems. Studies with actively loaded vesicles also suggested that heavy SR vesicles contain a Ca2+ permeation system that is inhibited by calmodulin.
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000494:pharmacology*; D002417:Cattle; D007093:Imidazoles / Q000494:pharmacology*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009132:Muscles / Q000378:metabolism*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D014268:Trifluoperazine / Q000494:pharmacology*; D003189:p-Methoxy-N-methylphenethylamine / Q000494:pharmacology*
chemical_list: D002132:Calcium Radioisotopes; D002147:Calmodulin; D007093:Imidazoles; D014268:Trifluoperazine; C005147:5'-adenylyl (beta,gamma-methylene)diphosphonate; D003189:p-Methoxy-N-methylphenethylamine; C031938:calmidazolium; D000255:Adenosine Triphosphate; D008274:Magnesium; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D002118:Calcium