Table I

Parameters used for the calculations

123456
Calcium  Dbuf  k1,buf  k−1,buf  Kd,buf  [buf]R
buffer
10−6cm2s1  108M1s1  s1  μM  mM
EGTA     1.7§    0.025§    1.485§  0.594  18.24
ATP     1.4    0.136  30,000  2,200   5.5
troponin     0  0.575*   115*    0.42§
fura-2  0.54    0.7   30§  0.43   0.05-6
123456
Calcium  Dbuf  k1,buf  k−1,buf  Kd,buf  [buf]R
buffer
10−6cm2s1  108M1s1  s1  μM  mM
EGTA     1.7§    0.025§    1.485§  0.594  18.24
ATP     1.4    0.136  30,000  2,200   5.5
troponin     0  0.575*   115*    0.42§
fura-2  0.54    0.7   30§  0.43   0.05-6

Column 1 gives the name of the Ca buffer. Column 2 gives the value of the diffusion coefficient in myoplasm. Columns 3 and 4 give the values of the apparent forward and backward rate constants for Ca complexation. Column 5 gives the values of the apparent dissociation constant, equal to the ratio of the values in columns 4 and 3. Column 6 gives the resting concentrations that were used for the calculations. The values in columns 4 and 5 for EGTA are estimated for pH = 6.9. The value in column 6 for troponin gives the concentration of Ca-regulatory sites on troponin (expressed in terms of myoplasmic concentration in the I-band) for a sarcomere length of 3.6 μm, with the assumption that all the troponin lies on the thin filaments, which have a length of 2.05 μm (Page and Huxley, 1963); the value of 0.42 mM for the concentration in the I-band corresponds to a spatially averaged myoplasmic concentration of (2.05/3.6)0.42 = 0.24 mM, as estimated by Baylor et al. (1983). Values of other parameters are DCa = 3 × 10−6 cm2 s−1 (Pape et al., 1995), and, unless noted otherwise, øpoint = 0.5 × 106 ions s−1 (which corresponds to 0.16 pA). In the equations in Appendix C, αATP = Kd,ATP−1).

*

Baylor et al. (1983),

Pape et al. (1993),

§

Pape et al. (1995),

Baylor and Hollingworth (1998).

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