Spatial distribution of dihydropyridine receptors in the plasma membrane of guinea pig cardiac myocytes investigated by correlative confocal microscopy and label-fracture electron microscopy.
Excitation-contraction coupling in cardiac muscle is thought to depend fundamentally on the spatial organization of sarcolemmal dihydropyridine receptors (L-type calcium channels) in relation to ryanodine receptors (calcium-release channels of the sarcoplasmic reticulum). In the present study, we have investigated the distribution of dihydropyridine receptors in the guinea pig myocyte plasma membrane by correlative immunoconfocal microscopy and label-fracture electron microscopy. Label-fracture, a method in freeze-fracture cytochemistry, permits immunogold localization of cell surface proteins in en face membrane views. Taken together, results from confocal microscopy and label-fracture replicas suggest that, in the peripheral plasma membrane, calcium channels are organized predominantly in the form of clusters. Confocal microscopy also suggests a similar organization in the transverse tubules. It is hypothesized that these clusters may lie adjacent to junctional sarcoplasmic reticulum, permitting the close coupling of influx of calcium through plasma membrane calcium channels to trigger release of calcium from the intracellular stores, as part of the mechanism of calcium-induced calcium release.
Takagishi
Y
Y
Imperial College School of Medicine, National Heart and Lung Institute, Royal Brompton Hospital, London, UK.
Rothery
S
S
Issberner
J
J
Levi
A
A
Severs
N J
NJ
D000818:Animals; D015220:Calcium Channels / Q000032:analysis*; D020746:Calcium Channels, L-Type; D002462:Cell Membrane / Q000737:chemistry; D019084:Fluorescent Antibody Technique, Indirect; D005614:Freeze Fracturing; D006168:Guinea Pigs; D018613:Microscopy, Confocal / Q000379:methods*; D016253:Microscopy, Immunoelectron / Q000379:methods*; D009206:Myocardium / Q000737:chemistry* / Q000166:cytology
D015220:Calcium Channels; D020746:Calcium Channels, L-Type