Utilization of fatigued and non-fatigued isolated guinea-pig papillary muscles and ventricular myocytes on the comparison of inotropic, chronotropic and intracellular calcium changes induced by monensin and digoxin

Abstract

We investigated four different concentrations of digoxin (0.3,1,3 and 10 junol/1) and three different concentrations of monensin (2,7 and 12 |amol/l) on the contraction force of guinea-pig papillary muscles. The highest increase in contraction force was obtained by using 3 |imol/l digoxin or 7 ^mol/1 monensin. These concentrations were chosen for subsequent experiments to study the effects of these drugs on contraction force (CF), initial contraction velocity (ICV), averse contraction velocity (ACV), initial relaxation velocity (IRV) and stimulus to response time (ST) change in fatigued (defined as the level at which papillary muscle contraction had lost 30% of its original contraction force with the elapse of time) and non-fatigued guinea-pig papillary muscles. The five hours of measurement in Experiment 3 were divided into five periods (TO was equilibration, Tl, T2, T3, and T4 were respectively one, two, three, and four hours after drug administration). We found that both monensin and digoxin increased the CF and ACV at Tl and increased the IRV at T2. Digoxin lost its effect with the elapse of time while monensin did not Digoxin also