title: The differential effects of twitch potentiators on charge movements in frog skeletal muscle.
abstract: The effects of twitch potentiators at physiologically effective concentrations on intramembrane charge movements were examined in voltage-clamped frog skeletal muscle in the presence and absence of tetracaine. Caffeine, even at high concentrations (2.5 mM) did not alter the potential dependence of either tetracaine-sensitive or tetracaine-resistant portions of non-linear charge through a voltage range that included the mechanical threshold. Perchlorate (8 mM) altered the form and shifted the potential dependence of the non-linear charge by about -25 mV in the hyperpolarizing direction, but did not alter the total available charge. Comparing charge movements in the presence and absence of 4 mM-tetracaine demonstrated that perchlorate shifted the threshold and voltage dependence of the delayed ('q gamma') transients but had no action on the steady-state tetracaine-resistant charge. Thiocyanate (10 mM) shifted the voltage dependence of charge movements by about 20 mV in the hyperpolarizing direction. Experiments employing 4 mM-tetracaine demonstrated that this was the result of effects on both tetracaine-sensitive and tetracaine-resistant charge movements. On the basis of their effects on contractile activation reported on earlier occasions, these differential effects of twitch potentiators are explicable in terms of tetracaine-sensitive and tetracaine-resistant charge components being causally separate and not requiring a direct participation of tetracaine-resistant charge in contractile activation.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects*; D009132:Muscles / Q000502:physiology*; D010472:Perchlorates / Q000494:pharmacology; D011896:Rana temporaria; D017670:Sodium Compounds; D013748:Tetracaine / Q000494:pharmacology; D013861:Thiocyanates / Q000494:pharmacology
chemical_list: D010472:Perchlorates; D017670:Sodium Compounds; D013861:Thiocyanates; D013748:Tetracaine; D002110:Caffeine; C031068:sodium perchlorate; C031760:thiocyanate