title: Twitch activation in Ca2+ -free solutions in the myotomes of the lancelet (Branchiostoma lanceolatum).
abstract: The question of whether a Ca2+ influx is necessary to activate twitches in the very thin myotome cells of the lancelet was reinvestigated. Though twitches were blocked in EGTA containing Ca2+- free bathing solutions, they reappeared under certain conditions: a) when the Mg2+ level was lowered, b) when small amounts of caffeine were added, and c) when Cl- in the bathing solution was partly replaced by SCN-. In Ca2+ -containing solutions the changes a) to c) increased the twitch height. The results suggest that a Ca2+ release from the intracellular stores is involved in twitch activation and that external Ca2+ modifies the coupling between excitation and Ca2+ release rather than initiating contractile activation.
mesh_terms: D000200:Action Potentials; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002816:Chordata, Nonvertebrate / Q000502:physiology*; D007454:Iodides / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000378:metabolism*; D009566:Nitrates / Q000494:pharmacology; D013861:Thiocyanates / Q000494:pharmacology
chemical_list: D007454:Iodides; D009566:Nitrates; D013861:Thiocyanates; D002110:Caffeine; D008274:Magnesium; D002118:Calcium