Effects of amrinone on the electromechanical coupling in frog skeletal muscle fibres.
The contractile effects of 1.1 mM amrinone were studied on isolated skeletal muscle fibres of the frog (2-5 degrees C, slack length). Amrinone potentiated the twitch amplitude and the maximum tetanic tension and also enhanced the maximum contracture response elicited by 117.5 mM K+ (mean increase 6.3 +/- 1.8%, n = 6, P less than 0.02). The time to half-relaxation of the potassium contracture was slightly increased (mean change 13.8 +/- 3.5%, n = 7, P less than 0.01). Amrinone furthermore shifted the S-shaped curve relating contracture tension to log K+ to the left, and thus reduced the threshold depolarization (the mechanical threshold) needed to elicit a contracture (mean reduction 11 +/- 1 mV). The duration of the action potential at the -25 mV level was slightly increased by amrinone, whereas the resting membrane potential was unaffected.
Mörner
S E
SE
Department of Pharmacology, University of Lund, Sweden.
Månsson
A
A
D000200:Action Potentials / Q000187:drug effects; D000676:Amrinone / Q000494:pharmacology*; D000818:Animals; D001696:Biomechanical Phenomena; D004056:Differential Threshold; D004594:Electrophysiology; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000187:drug effects* / Q000502:physiology; D011188:Potassium / Q000494:pharmacology; D011896:Rana temporaria; D011930:Reaction Time
D000676:Amrinone; D011188:Potassium