Characterization of the calcium release domains during excitation-contraction coupling in skeletal muscle fibres.
The spatiotemporal properties of the Ca2+ release process in skeletal muscle fibres were determined using a confocal spot detection system. The low-affinity, fluorescent Ca2+ indicator Oregon Green 488 BAPTA-5N (OGB-5N) was used to record localized, action potential-induced fluorescence signals from consecutive locations separated by 200 nm within a single sarcomere. Three-dimensional reconstructions of the Ca2+ transients illustrated the existence of fluorescence domains around Ca2+ release sites, which are centred at the T-tubules. By constructing isochronal plots, it was estimated that the earliest detectable full width at half-maximum (FWHM) of the Ca2+ domains was 0.77+/-0.08 microm and increased rapidly with time to 1.4+/-0.04 microm at peak (17-18 degrees C). A delay of 0.64+/-0.1 ms was observed between the onset of the fluorescence transients at the Z- and M-lines. Deconvolution of fluorescence transients gave estimates of approximately 9 and 2 microM for the peak [Ca2+] changes at the Z and M-lines, respectively. Our results are compatible with the possibility that action potential stimulation elicits Ca2+ release from a region of the sarcoplasmic reticulum (SR) broader than the T-SR junction.
DiFranco
Marino
M
Department of Physiology, UCLA School of Medicine, 10833 Le Conte Avenue 53-263 CHS, Los Angeles, CA 90095-1751, USA.
Novo
David
D
Vergara
Julio L
JL
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002264:Carboxylic Acids; D002614:Chelating Agents; D004533:Egtazic Acid / Q000031:analogs & derivatives*; D004594:Electrophysiology; D005456:Fluorescent Dyes; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology*; D011892:Rana catesbeiana; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
D002264:Carboxylic Acids; D002614:Chelating Agents; D005456:Fluorescent Dyes; C436864:Oregon Green 488 carboxylic acid; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium