Ignition of calcium sparks in arterial and cardiac muscle through caveolae.
Ca(2+) sparks are localized intracellular Ca(2+) events released through ryanodine receptors (RyRs) that control excitation-contraction coupling in heart and smooth muscle. Ca(2+) spark triggering depends on precise delivery of Ca(2+) ions through dihydropyridine (DHP)-sensitive Ca(2+) channels to RyRs of the sarcoplasmic reticulum (SR), a process requiring a very precise alignment of surface and SR membranes containing Ca(2+) influx channels and RyRs. Because caveolae contain DHP-sensitive Ca(2+) channels and may colocalize with SR, we tested the hypothesis that caveolae are the structural element necessary for the generation of Ca(2+) sparks. Using methyl-ss-cyclodextrin (dextrin) to deplete caveolae, we found that dextrin dose-dependently decreased the frequency, amplitude, and spatial size of Ca(2+) sparks in arterial smooth muscle cells and neonatal cardiomyocytes. However, temporal characteristics of Ca(2+) sparks were not significantly affected. We ruled out the possibility that the decreases in Ca(2+) spark frequency and size are caused by changes in DHP-sensitive L-type channels, SR Ca(2+) load, or changes in membrane potential. Our results suggest a novel signaling model that explains the formation of Ca(2+) sparks in a caveolae microdomain. The transient elevation in [Ca(2+)](i) at the inner mouth of a single caveolemmal Ca(2+) channel induces simultaneous activation and thus opens several RyRs to generate a local Ca(2+) release event, a Ca(2+) spark. Alterations in the molecular assembly and ultrastructure of caveolae may lead to pathophysiological changes in Ca(2+) signaling. Thus, caveolae may be intimately involved in cardiovascular cell dysfunction and disease.
Löhn
M
M
Franz Volhard Clinic and Max Delbrück Center for Molecular Medicine, Charité University Hospitals, Humboldt University of Berlin, Germany.
Fürstenau
M
M
Sagach
V
V
Elger
M
M
Schulze
W
W
Luft
F C
FC
Haller
H
H
Gollasch
M
M
D000375:Aging / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D021941:Caveolae / Q000378:metabolism* / Q000648:ultrastructure; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D002469:Cell Separation; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D003505:Cyclodextrins / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D047392:beta-Cyclodextrins
D020746:Calcium Channels, L-Type; D003505:Cyclodextrins; D010726:Phosphodiesterase Inhibitors; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D012433:Ryanodine; D002110:Caffeine; D002784:Cholesterol; D002118:Calcium