Calcium transients in developing mouse skeletal muscle fibres.
Ca(2)(+) transients elicited by action potentials were measured using MagFluo-4, at 20-22 degrees C, in intact muscle fibres enzymatically dissociated from mice of different ages (7, 10, 15 and 42 days). The rise time of the transient (time from 10 to 90% of the peak) was 2.4 and 1.1 ms in fibres of 7- and 42-day-old mice, respectively. The decay of the transient was described by a double exponential function, with time constants of 1.8 and 16.4 ms in adult, and of 4.6 and 105 ms in 7-day-old animals. The fractional recovery of the transient peak amplitude after 10 ms, F(2(10))/F(1), determined using twin pulses, was 0.53 for adult fibres and ranged between 0.03 and 0.60 in fibres of 7-day-old animals This large variance may indicate differences in the extent of inactivation of Ca(2)(+) release, possibly related to the difference in ryanodine receptor composition between young and old fibres. At the 7 and 10 day stages, fibres responded to Ca(2)(+)-free solutions with a larger decrease in the transient peak amplitude (25% versus 11% in adult fibres), possibly indicating a contribution of Ca(2)(+) influx to the Ca(2)(+) transient in younger animals. Cyclopiazonic acid (1 mum), an inhibitor of the sarcoplasmic reticulum (SR) Ca(2)(+)-ATPase, abolished the Ca(2)(+) transient decay in fibres of 7- and 10-day-old animals and significantly reduced its rate in older animals. Analysis of the transients with a Ca(2)(+) removal model showed that the results are consistent with a larger relative contribution of the SR Ca(2)(+) pump and a lower expression of myoplasmic Ca(2)(+) buffers in fibres of young versus old animals.
Capote
Joana
J
[corrected] Instituto Venezolano de Investigaciones Cientificas IVIC, Apartado 21827, Caracas 1020A, Venezuela.
Bolaños
Pura
P
Schuhmeier
Ralph Peter
RP
Melzer
Werner
W
Caputo
Carlo
C
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000494:pharmacology / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000254:growth & development*
D007211:Indoles; D002118:Calcium; C000543:cyclopiazonic acid
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