Contractions induced by sodium withdrawal in crab (Callinectes danae) muscle fibres.
A study was made of the effects of Na removal on the resting tension of single muscle fibres of the crab Callinectes danae. Reduction of [Na]o (replacement with Li, Tris or choline) below a threshold value, typical for each fibre, induced spontaneous, local contractions randomly dispersed along the fibres; this was followed by propagated contractile waves and tension oscillations. Sustained contractures were occasionally seen at threshold [Na]o and were consistently observed when [Na]o was further reduced. The Na withdrawal contractions depended on [Ca]o and were abolished in Ca-free media; they were restored within seconds after the addition of Ca (3-12 mM) or Sr (15-25 mM), but not Ba (10-100 mM), to the media. Caffeine (0.2-1.0 mM) facilitated, whereas La (2-5 mM), procaine (1 mM) or lidocaine (10 mM) inhibited the Na-withdrawal contractions. It is concluded that increased Ca influx across the sarcolemma and release of stored Ca from the sarcoplasmic reticulum are involved in the contractions induced by Na-deficient solutions in crab fibres.
D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D003386:Brachyura / Q000502:physiology*; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology; D002794:Choline / Q000494:pharmacology; D066298:In Vitro Techniques; D008094:Lithium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D012684:Sensory Thresholds / Q000187:drug effects; D012964:Sodium / Q000494:pharmacology*; D014325:Tromethamine / Q000494:pharmacology
D000779:Anesthetics, Local; D002413:Cations, Divalent; D014325:Tromethamine; D002110:Caffeine; D008094:Lithium; D012964:Sodium; D002794:Choline; D002118:Calcium