title: Calcium action potentials in innervated and denervated rat muscle fibres.
abstract: We studied the generation of calcium action potentials (Ca APs) in innervated and denervated fibres of the extensor digitorum longus of the rat in a tetraethylammonium (TEA) sulphate solution plus 3-4 diaminopiridine (3-4 DAP). The main results are the following: (1) more than 90% of the innervated fibres were capable of developing well-sustained Ca APs that were blocked by Cd or nifedipine; (2) the incidence of Ca APs obtained from the denervated fibres was substantially lower than in the control preparations; (3) no relation was found between the appearance of Ca APs in the denervated fibres and the resting membrane potential (Vm), stimulus duration (500-2000 ms) or holding potential (-80, -100 mV); (4) The percentage of denervated fibres that exhibited Ca APs was increased significantly with the following procedures. First, by raising the external Ca concentration to 14 mM; second, by depleting the intracellular K concentration by overnight exposure of the muscles to a free K-Cs solution; (c) and third, by incubating the muscles in 500 nM apamin, a venom that inhibits the K conductance activated by Ca. Several factors may be involved in the lower incidence of Ca APs obtained in denervated fibres: (1) a diminished Ca current due to a reduction in the driving force as a result of an increment in the intracellular Ca concentration; (2) a persistence of a shunting K conductance that is not inhibited by TEA and 3-4 DAP; (3) a shift in the voltage dependence of the activation and inactivation parameters of the Ca current or the appearance of a new type of Ca channel with a different kinetics.
authors.affiliation: Instituto de Investigaciones Médicas A. Lanari, UBA, Buenos Aires, Argentina.
authors.forename: O
authors.initials: O
authors.lastname: Delbono
authors.forename: B A
authors.initials: BA
authors.lastname: Kotsias
mesh_terms: D015761:4-Aminopyridine / Q000031:analogs & derivatives / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000077770:Amifampridine; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D004553:Electric Conductivity; D009121:Muscle Denervation; D009132:Muscles / Q000294:innervation* / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D013757:Tetraethylammonium Compounds; D002104:Cadmium; D001030:Apamin; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D009543:Nifedipine; D000077770:Amifampridine; D002118:Calcium