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Review
. 1999 Mar;113(3):377-84.
doi: 10.1085/jgp.113.3.377.

Calcium sparks: release packets of uncertain origin and fundamental role

N Shirokova  1 , A González, W G Kirsch, E Ríos, G Pizarro, M D Stern, H Cheng
Affiliations
Review

Calcium sparks: release packets of uncertain origin and fundamental role

N Shirokova et al. J Gen Physiol. 1999 Mar.
No abstract available

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Figures

Figure 1
Figure 1
Simulations of sparks for three Ca2+ currents represented at top, of 2, 5, and 25 pA, lasting 6 ms, originating at even density from a 0.2-μm radius sphere and entering a homogeneous medium with distributed Ca2+ removal properties that simulate skeletal muscle. (Middle) Time dependence of fluorescence in the central pixel of simulated line scan image. (Inset) Peak increase in fluorescence, ΔF/F 0, vs. current; the line is traced through the first two points. (Bottom) Normalized spatial profile at the time of maximum fluorescence. Note: (a) near linearity between peak fluorescence and release current, (b) agreement between rise time and open channel time, (c) spark amplitude within the range observed experimentally, even at the largest current, and (d) the FWHM (in spatial profile) is ∼1 μm (while the experimental values are 1.5–2 μm). Details of simulation in Ríos et al. (manuscript submitted for publication). Diffusion coefficients (μm2 ms−1): Ca2+, 0.35; dye (free or Ca2+-bound), 0.02; EGTA (free or Ca2+-bound), 0.036; ATP, 0.14; parvalbumin (parv), 0.016. Association rate constants (mM−1 ms−1): Ca:dye, 32; Ca:EGTA, 2; Ca:troponin, 5.7; Ca:ATP, 150; Ca:parv, 125; Ca:pump, 500; Mg:ATP, 1.95; Mg: parv, 0.03. Dissociation rate constants (ms−1): Ca:dye, 0.033; Ca: EGTA, 0.002; Ca:pump, 0.5; Ca:ATP, 30; Mg:ATP, 0.195; Ca:parv, 0.0005; Mg:parv, 0.003; Ca:troponin, 0.0114. Maximum SR pump rate, 0.0098 mM/ms. Total concentrations (mM):dye, 0.15; pump sites, 0.24; parv, 1; troponin, 0.24; EGTA, 1; ATP, 5; [Mg2+], 0.15 (taken to be constant). Spark blurred with FWHMx = FWHMy = 0.33 μm, FWHMz = 1.0 μm.
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