title: Voltage-gated Ca(2+) influx through L-type channels contributes to sarcoplasmic reticulum Ca(2+) loading in skeletal muscle.
abstract: Muscle contraction is triggered by Ca(2+) ions released from the sarcoplasmic reticulum (SR) in response to depolarization of skeletal muscle fibres. Muscle activation is also associated with a voltage-activated trans-sarcolemmal Ca(2+) influx early identified as a current flowing through L-type Ca(2+) channels. Because removal of external Ca(2+) does not impede fibres from contracting, a negligible role was given to this voltage-activated Ca(2+) entry, although the decline of Ca(2+) release is more pronounced in the absence of Ca(2+) during long-lasting activation. Furthermore, it is not clearly established whether Ca(2+) exclusively flows through L-type channels or in addition through a parallel voltage-activated pathway distinct from L-type channels. Here, by monitoring the quenching of fura-2 fluorescence resulting from Mn(2+) influx in voltage-controlled mouse and zebrafish isolated muscle fibres, we show that the L-type current is the only contributor to Ca(2+) influx during long-lasting depolarizations in skeletal muscle. Calibration of the Mn(2+) quenching signal allowed us to estimate a mean Mn(2+) current of 0.31 ± 0.06 A F(-1) flowing through L-type channels during a train of action potentials. Measurements of SR Ca(2+) changes with fluo-5N in response to depolarization revealed that an elevated voltage-activated Ca(2+) current potentiated SR Ca(2+) loading and addition of external Mn(2+) produced quenching of fluo-5N in the SR, indicating that voltage-activated Ca(2+) /Mn(2+) influx contributes to SR Ca(2+) /Mn(2+) loading.
authors.affiliation: Université de Lyon, Université Lyon 1, CNRS UMR 5534, Centre de Génétique et de Physiologie Moléculaire et Cellulaire, Villeurbanne, France.
authors.forename: Gaëlle
authors.initials: G
authors.lastname: Robin
authors.affiliation: Université de Lyon, Université Lyon 1, CNRS UMR 5534, Centre de Génétique et de Physiologie Moléculaire et Cellulaire, Villeurbanne, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Allard
mesh_terms: D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D020013:Calcium Signaling; D002478:Cells, Cultured; D008345:Manganese / Q000378:metabolism; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D015027:Zebrafish
chemical_list: D020746:Calcium Channels, L-Type; D008345:Manganese; D002118:Calcium