The influence of dantrolene, diazepam, pentobarbital and 4-aminopyridine on shortening induced depression in isolated muscle fibres of the frog.
The influence of dantrolene, diazepam, pentobarbital and 4-aminopyridine on the depressant effect of active shortening during twitch and tetanus was investigated in isolated muscle fibres of the frog. These drugs are all presumed to alter the kinetics of the release and re-uptake of activator calcium during the excitation-contraction process. The shortening induced depression was calculated as the difference in redeveloped force after a small (control) and a larger (test) release step and was expressed in per cent of the control. The depressant effect in response to a given amount of shortening during twitch contraction as well as during the plateau of a tetanus was approximately doubled after addition of 10 microM dantrolene. In contrast, diazepam (150 microM) reduced the shortening effect during the twitch to about one tenth of the value obtained in ordinary Ringer solution, while the force depression by shortening during tetanic stimulation remained essentially unaltered. Pentobarbital (1.0 mM) reduced the shortening induced depression during the twitch by 95-100%. 4-aminopyridine (3.0 mM) completely abolished the depressant effect of shortening obtained during the twitch and approximately halved the shortening effect during tetanic contraction.
D015761:4-Aminopyridine; D000631:Aminopyridines / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D003620:Dantrolene / Q000494:pharmacology*; D003975:Diazepam / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009132:Muscles / Q000378:metabolism; D010424:Pentobarbital / Q000494:pharmacology*; D011896:Rana temporaria
D000631:Aminopyridines; D015761:4-Aminopyridine; D003620:Dantrolene; D010424:Pentobarbital; D003975:Diazepam; D002118:Calcium