Voltage-activated elementary calcium release events in isolated mouse skeletal muscle fibers.
The elementary Ca(2+)-release events underlying voltage-activated myoplasmic Ca(2+) transients in mammalian muscle remain elusive. Here, we looked for such events in confocal line-scan (x,t) images of fluo-3 fluorescence taken from isolated adult mouse skeletal muscle fibers held under voltage-clamp conditions. In response to step depolarizations, spatially segregated fluorescence signals could be detected that were riding on a global increase in fluorescence. These discrete signals were separated using digital filtering in the spatial domain; mean values for their spatial half-width and amplitude were 1.99 +/- 0.09 microm and 0.16 +/- 0.005 DeltaF/F(0) (n = 151), respectively. Under control conditions, the duration of the events was limited by the pulse duration. In contrast, in the presence of maurocalcine, a scorpion toxin suspected to disrupt the process of repolarization-induced ryanodine receptor (RyR) closure, events uninterrupted by the end of the pulse were readily detected. Overall results establish these voltage-activated low-amplitude local Ca(2+) signals as inherent components of the physiological Ca(2+)-release process of mammalian muscle and suggest that they result from the opening of either one RyR or a coherently operating group of RyRs, under the control of the plasma membrane polarization.
Csernoch
Laszlo
L
Department of Physiology, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary.
Pouvreau
Sandrine
S
Ronjat
Michel
M
Jacquemond
Vincent
V
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004594:Electrophysiology / Q000379:methods; D066298:In Vitro Techniques; D051379:Mice; D018613:Microscopy, Confocal; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism* / Q000502:physiology*; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology; D013997:Time Factors
D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium