Confocal imaging of calcium release events in single smooth muscle cells.
Localized [Ca2+]i transients ('sparks') first directly detected in cardiac myocytes were considered to represent 'elementary' Ca(2+)-release events playing a key role during excitation-contraction coupling (Cheng et al. 1993). In this study we employed confocal [Ca2+]i imaging to characterize subcellular calcium signalling in fluo-3 loaded visceral and vascular smooth muscle cells. In some experiments membrane potential of the myocyte was controlled using whole-cell patch clamp technique and changes in membrane current were recorded simultaneously with [Ca2+]i imaging. Some local [Ca2+]i transients were very similar to 'Ca2+ sparks' observed in heart, i.e. lasting approximately 200 ms with a peak fluorescence ratio of 1.75 +/- 0.23 (mean +/- SD, n = 33). Ca2+ sparks were found to occur in certain preferred locations in the cell, termed frequent discharge sites. Other events were faster and smaller, lasting only approximately 40 ms with a peak normalized fluorescence of 1.36 +/- 0.09 (mean +/- SD, n = 28). A high correlation between spontaneous transient outward currents and spark occurrence was observed. Proliferating waves of elevated [Ca2+]i initiated during membrane depolarization seem to arise from spatio-temporal recruitment of local Ca(2+)-release events. The spatial non-uniformity of sarcoplasmic reticulum and ryanodine receptor distribution within the cell may account for the existence of 'frequent discharge sites' and the wide variation in the Ca2+ wave propagation velocities observed.
Bolton
T B
TB
Department of Pharmacology and Clinical Pharmacology, St. George's Hospital Medical School, London, UK.
Gordienko
D V
DV
D000814:Aniline Compounds; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D005456:Fluorescent Dyes; D006168:Guinea Pigs; D007082:Ileum / Q000166:cytology / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D008638:Mesenteric Arteries / Q000166:cytology / Q000502:physiology; D018613:Microscopy, Confocal; D009119:Muscle Contraction / Q000502:physiology; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D014966:Xanthenes
D000814:Aniline Compounds; D005456:Fluorescent Dyes; D014966:Xanthenes; C059715:Fluo-3; D002118:Calcium