Calcium transients in single fibers of low-frequency stimulated fast-twitch muscle of rat.
Ca(2+) transients were investigated in single fibers isolated from rat extensor digitorum longus muscles exposed to chronic low-frequency stimulation for different time periods up to 10 days. Approximately 2.5-fold increases in resting Ca(2+) concentration ([Ca(2+)]) were observed 2 h after stimulation onset and persisted throughout the stimulation period. The elevated [Ca(2+)] levels were in the range characteristic of slow-twitch fibers from soleus muscle. In addition, we noticed a transitory elevation of the integral [Ca(2+)] per pulse with a maximum ( approximately 5-fold) after 1 day. Steep decreases in rate constant of [Ca(2+)] decay could be explained by an immediate impairment of Ca(2+) uptake and, with longer stimulation periods, by an additional loss of cytosolic Ca(2+) binding capacity resulting from a decay in parvalbumin content. A partial recovery of the rate constant of [Ca(2+)] decay in 10-day stimulated muscle could be explained by an increasing mitochondrial contribution to Ca(2+) sequestration.
Carroll
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S
Faculty of Biology, University of Konstanz, D-78457 Constance, Germany.
Nicotera
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P
Pette
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D
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002454:Cell Differentiation; D004594:Electrophysiology; D006706:Homeostasis / Q000502:physiology; D007037:Hypothyroidism / Q000378:metabolism; D007536:Isomerism; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D018656:Muscle Fibers, Fast-Twitch / Q000166:cytology / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000166:cytology / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000201:enzymology; D018995:Myosin Heavy Chains / Q000737:chemistry / Q000378:metabolism; D010320:Parvalbumins / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000201:enzymology
D002021:Buffers; D010320:Parvalbumins; D000255:Adenosine Triphosphate; D018995:Myosin Heavy Chains; D000252:Calcium-Transporting ATPases; D002118:Calcium