Calcium concentration and movement in the ventricular cardiac cell during an excitation-contraction cycle.
This paper extends the model for Ca movement in the cardiac ventricular cell from the diadic cleft space to the entire sarcomere. The model predicts the following: 1) Shortly after SR release there is a [Ca] gradient >3 orders of magnitude from cleft center to M-line which, 50 ms after release, is still >30. Outside the cleft, 40 ms after cessation of release, the axial gradient from Z to M-line is >3. 2) At the end of SR release, >50% of the total Ca released is bound to low-affinity inner sarcolemmal phospholipid binding sites within the cleft. 3) Halving the SR release almost doubles the fraction of release removed from the cell via Na/Ca exchange and reduces average sarcomeric free [Ca] by 70%. 4) Adding 100 microM fluo-3, which doubles the buffering capacity of the cytoplasm, reduces peak average sarcomeric [Ca] by >50% and increases the initial half-time for [Ca] decrease by approximately twofold. 5) A typical Ca "spark" can be generated by an SR release 20% of maximum (4 x 10(-20) moles) over 2 ms. Fluo-3 (100 microM) significantly "shrinks" the spark. 6) The "spark" is a consequence of elementary events within the diadic cleft space. For example, removal of cleft binding sites would cause average sarcomeric Ca to increase by >10 fold, fall 10 times more rapidly, decrease latency for appearance of the spark by >20 times, and reduce spark duration by 85%. 7) Dividing SR Ca release between cleft and corbular SR produces a secondary [Ca] peak and a "flattening" of the sarcomeric [Ca] transient. These changes probably could not be resolved with current confocal microscopic techniques.
Peskoff
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A
Department of Physiology, UCLA School of Medicine, Los Angeles, California 90095-1760, USA. apeskoff@ucla.edu
Langer
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GA
D000814:Aniline Compounds; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D020746:Calcium Channels, L-Type; D004058:Diffusion; D005456:Fluorescent Dyes; D006321:Heart / Q000502:physiology*; D006352:Heart Ventricles; D007700:Kinetics; D008856:Microscopy, Fluorescence; D008955:Models, Cardiovascular; D008961:Models, Structural; D009200:Myocardial Contraction / Q000502:physiology*; D012518:Sarcomeres / Q000502:physiology*; D013997:Time Factors; D014966:Xanthenes
D000814:Aniline Compounds; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D005456:Fluorescent Dyes; D014966:Xanthenes; C059715:Fluo-3; D002118:Calcium