title: Excitation-induced Ca(2+) influx in rat soleus and EDL muscle: mechanisms and effects on cellular integrity.
abstract: In rat skeletal muscle, electrical stimulation increases Ca(2+) influx leading to progressive accumulation of calcium. Excitation-induced Ca(2+) influx in extensor digitorum longus (EDL; fast-twitch fibers) and soleus muscle (slow-twitch fibers) is compared. In EDL and soleus, stimulation at 40 Hz increased (45)Ca uptake 34- and 21-fold and (22)Na uptake 17- and 7-fold, respectively. These differences may be related to the measured 70% higher concentration of Na(+) channels in EDL. Repeated stimulation at 40 Hz elicited a delayed release of lactic acid dehydrogenase (LDH) from EDL (11-fold increase) and soleus (5-fold increase). Continuous stimulation at 1 Hz increased LDH release only from EDL (18-fold). This was associated with increased Ca(2+) content and was augmented at high extracellular Ca(2+) concentration ([Ca(2+)](o)) and suppressed at low [Ca(2+)](o). The data support the hypothesis that excitation-induced Ca(2+) influx is mediated in part by Na(+) channels and that the ensuing increase in intracellular Ca(2+) induces cellular damage. This is most pronounced in EDL, which may account for the repeated observation that prolonged exercise leads to preferential damage to fast-twitch fibers.
authors.affiliation: Department of Physiology, University of Aarhus, DK-8000 Arhus C, Denmark. HGN@fi.au.dk
authors.forename: H
authors.initials: H
authors.lastname: Gissel
authors.forename: T
authors.initials: T
authors.lastname: Clausen
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D004558:Electric Stimulation; D005260:Female; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000166:cytology / Q000201:enzymology*; D018482:Muscle, Skeletal / Q000166:cytology* / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000502:physiology; D012979:Sodium Radioisotopes; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D002132:Calcium Radioisotopes; D015222:Sodium Channels; D012979:Sodium Radioisotopes; D013779:Tetrodotoxin; D007770:L-Lactate Dehydrogenase; D002118:Calcium