Pharmacological studies of charge movement in frog skeletal muscle.
Charge movements in frog twitch fibres were studied using the three-microelectrode voltage-clamp technique. In a solution made moderately hypertonic with 350 mM-sucrose, fibre contraction was effectively blocked and a secondary hump appeared in the decay phase of the 'on' part of charge movement. At small depolarizations, the hump (Q gamma) is small and slow. As depolarization is increased, Q gamma becomes larger in magnitude and faster in kinetics until it merges with the main part of charge movement (Q beta). As the fibre is perfused extracellularly with a test solution saturated with dantrolene sodium, Q gamma disappears in about 30 min whereas the kinetics of Q beta are slowed down. After equilibration in the dantrolene sodium solution, the total moveable charge is reduced by about 20%, which could very well be the charge carried by Q gamma. Tetracaine also suppresses Q gamma but does not seem to have any effect on the kinetics of Q beta. The suppression of Q gamma appears to be dose-dependent, with complete abolition occurring at about 4 mM-tetracaine. Dissection of charge movement with tetracaine indicates that Q gamma might be bell-shaped and capacitive in nature. Q beta and Q gamma might be two distinct species of charge and Q gamma would probably be more closely associated with calcium release from the sarcoplasmic reticulum.
D000818:Animals; D003620:Dantrolene / Q000494:pharmacology; D006982:Hypertonic Solutions; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000502:physiology*; D011896:Rana temporaria; D013748:Tetracaine / Q000494:pharmacology
D006982:Hypertonic Solutions; D013748:Tetracaine; D003620:Dantrolene