title: Potassium-induced depolarizations and generation of tension in barnacle muscle fibres: effects of external calcium, strontium and barium.
abstract: Potassium-induced contractions were studied in muscle fibres from Megabalanus psittacus (Darwin) in an attempt to establish the requirement of extracellular calcium for the development of force. A sudden elevation of external potassium induced the production of contractures and/or twitches only if calcium was present. In calcium-free solutions no contraction or action potential occurred. When external calcium was replaced by barium, potassium-induced depolarizations accompanied by several action potentials did not generate either contractures or twitches. With strontium in place of calcium, action potentials of different duration were observed. Only the long-lasting ones (a few seconds) induced twitches.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001464:Barium / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D008274:Magnesium / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009129:Muscle Tonus / Q000187:drug effects; D009132:Muscles / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology*; D013324:Strontium / Q000494:pharmacology*; D001468:Thoracica
chemical_list: D001464:Barium; D008274:Magnesium; D011188:Potassium; D002118:Calcium; D013324:Strontium