Calcium sparks in human coronary artery smooth muscle cells resolved by confocal imaging.
OBJECTIVE
The observation of local 'elementary' Ca2+ release events (Ca2+ sparks) through ryanodine receptor (RyR) channels in the sarcoplasmic reticulum (SR) has changed our understanding of excitation-contraction (EC) coupling in cardiac and smooth muscle. In arterial smooth muscle, Ca2+ sparks have been suggested to oppose myogenic vasoconstriction and to influence vasorelaxation by activating co-localized Ca2+ activated K+ (K(Ca)) channels (STOCs). However, all prior studies on Ca2+ sparks have been performed in non-human tissues.


METHODS
In order to understand the possible significance of Ca2+ sparks to human cardiovascular function, we used high spatial resolution confocal imaging to record Ca2+ sparks in freshly-isolated, individual myocytes of human coronary arteries loaded with the Ca2+ indicator fluo-3.


RESULTS
Local SR Ca2+ release events recorded in human myocytes were similar to 'Ca2- sparks' recorded previously from non-human smooth muscle cells. In human myocytes, the peak [Ca2+]i amplitudes of Ca2+ sparks (measured as F/F0) and width at half-maximal amplitude were 2.3 and 2.27 microm, respectively. The duration of Ca2+ sparks was 62 ms. Ca2+ sparks were completely inhibited by ryanodine (10 micromol/l). Ryanodine-sensitive STOCs could be identified with typical properties of K(Ca) channels activated by Ca2+ sparks.


CONCLUSIONS
Our data implies that modern concepts suggesting an essential role of Ca2+ spark generation in EC coupling recently derived from non-human muscle are applicable to human cardiovascular tissue. Although the basic properties of Ca2+ sparks are similar, our results demonstrate that Ca2+ sparks in coronary arteries in humans, have features distinct from non-arterial smooth muscle cells of other species.
Fürstenau
M
M
Franz Volhard Clinic at the Max Delbrück Center for Molecular Medicine, Charité University Hospitals, Humboldt University Berlin, Germany.
Löhn
M
M
Ried
C
C
Luft
F C
FC
Haller
H
H
Gollasch
M
M
D000814:Aniline Compounds; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D003331:Coronary Vessels / Q000737:chemistry / Q000378:metabolism*; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D005260:Female; D005456:Fluorescent Dyes; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D018613:Microscopy, Confocal / Q000379:methods*; D009131:Muscle, Smooth, Vascular / Q000737:chemistry / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000737:chemistry / Q000378:metabolism; D014661:Vasoconstriction / Q000502:physiology; D014664:Vasodilation / Q000502:physiology; D014966:Xanthenes
D000814:Aniline Compounds; D002614:Chelating Agents; D005456:Fluorescent Dyes; D015221:Potassium Channels; D019837:Ryanodine Receptor Calcium Release Channel; D014966:Xanthenes; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D012433:Ryanodine; C059715:Fluo-3; D004533:Egtazic Acid; D002118:Calcium