Ca-dependent slow action potentials in neuromuscular diseases.
Slow Ca-dependent action potentials were studied in skeletal muscle fibers from different Neuromuscular Diseases (NMD). Biopsies were obtained from: 3 myopathies [Fascioscapulohumeral Dystrophy (FSH) and Polymyositis (PM)], 6 patients with other diseases (CD) [Amyotrophic Lateral Sclerosis (ALS), Central Core Disease, Mitochondrial Myopathy, Polyneuritis (PN), von Eulenberg's Paramyotonia], and 8 normal control muscles. Experiments were carried out in muscle fibers under current-clamp conditions. Membrane currents other than Ca ones were abolished or greatly diminished. Muscle fibers produced any of 3 types of responses, when stimulated by depolarizing pulses: fully developed Ca-action potentials (CaAP), abortive non-regenerative Ca responses (NrR), or only capacitive passive responses (WR). The 3 types of responses were not dependent on the basal conditions of the fibers. The frequency of observation of CaAPs was significantly higher in myopathic disease. In myopathies, 46% of the muscle fibers had CaAPs, while only 22% of fibers from CD and 15% of the fibers from normal muscles showed CaAPs. No differences were observed in the resting constants as well as in the CaAPs parameters between normal and diseased muscle fibers.
Nicola Siri
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Instituto de Biologia Celular, Facultad de Medicina, Universidad de Buenos Aires, Republica Argentina.
Dubrovsky
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Uchitel
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D000200:Action Potentials / Q000187:drug effects* / Q000502:physiology; D002118:Calcium / Q000494:pharmacology* / Q000502:physiology; D004594:Electrophysiology; D006801:Humans; D009132:Muscles / Q000166:cytology / Q000473:pathology / Q000503:physiopathology; D009468:Neuromuscular Diseases / Q000473:pathology / Q000503:physiopathology*
D002118:Calcium