THE THIADIAZINONE EMD-57033 SPEEDS THE ACTIVATION OF SKINNED CARDIAC-MUSCLE PRODUCED BY THE PHOTOLYSIS OF NITR-5

EMD 57033 is thought to produce its potentiating effect by increasing the apparent Ca2+ sensitivity of the myofilaments, possibly by alterin g the kinetics of actomyosin interaction. We have investigated the eff ect of 10 mu M EMD 57033 upon activation speed, induced by flash photo lysis of 2mM nitr-5 (caged Ca2+), in chemically skinned trabeculae fro m the guinea-pig at 12 degrees C. EMD 57033 increases the half time of activation from 238 +/- 18.5 msec (n=6) to 132.1 +/- 34.0 msec (n=8)( mean +/- s.e.m.) and suggests that this Ca2+ sensitiser has an importa nt effect upon f(app), that is the transition from the non-force to fo rce generating cross-bridge states