title: D600 prolongs inactivation of the contractile system in frog twitch fibres.
abstract: (1) Single twitch fibres were dissected from tibialis muscles of Rana temporaria and used to study the effect of D600 (gallopamil) on potassium-induced contractures. (2) 95 mM K-Ringer's was applied for 8-15 s at intervals of generally 2.5-5 min; at temperatures of 6-8 degrees C and in the absence of D600 the amplitude of the contractures remained fairly constant. After pretreatment with D600 (30 microM) a single (conditioning) K-contracture was sufficient to 'paralyze' the fibres (cf. Eisenberg et al. 1983). (3) Complete paralysis could also be achieved at 18-20 degrees C. In three fibres a single conditioning K-application was sufficient; in two more fibres two or three conditioning K-applications were required. (4) D600-paralysis could not only be achieved with high K-concentrations but also by conditioning with sub- or suprathreshold K-concentrations (20-40 mM); the duration of the conditioning periods required to induce complete paralysis was approximately the same before and after D600-treatment. (5) Contractures were partially abolished by application of 20-40 mM K-Ringer's for short conditioning periods; after D600-treatment the degree of contracture loss was similar. (6) At low temperature the state of partial or complete paralysis induced by subthreshold K-concentrations and D600 was maintained for long periods of time. (7) The presence of 10 mM Ca2+ did not protect the fibres from being paralyzed by treatment with D600 and high K-Ringer's at low temperature; however, more than one conditioning K-application was required.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D005711:Gallopamil / Q000494:pharmacology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology; D011896:Rana temporaria; D013696:Temperature
chemical_list: D005711:Gallopamil; D011188:Potassium; D002118:Calcium