Table 1. Concentrations and diffusion... | Rockefeller University Press

Table 1.

Concentrations and diffusion coefficients assumed in the model for frog twitch fibers and mouse fast-twitch fibers (16°C)

Constituent	Concentration	Concentration of binding-sites	Diffusion coefficient
	µM	µM	10⁻6 cm²/s
Free [Ca²⁺]	0.050 (resting)	−	3
Free [Mg²⁺]	1,000	−	−
Troponin	120	240 (Ca²⁺ regulatory sites)	0
SR Ca²⁺ pump	120	240 (Ca²⁺ regulatory sites)	0
Parvalbumin	750	1,500 (Ca²⁺/Mg²⁺ sites)	0.15
ATP	8,000	8,000 (Ca²⁺/Mg²⁺ sites)	1.4
Furaptra	100	100 (Ca²⁺/Mg²⁺ sites)	1.59
Protein	500	500 (furaptra sites)	0

Constituent	Concentration	Concentration of binding-sites	Diffusion coefficient
	µM	µM	10⁻6 cm²/s
Free [Ca²⁺]	0.050 (resting)	−	3
Free [Mg²⁺]	1,000	−	−
Troponin	120	240 (Ca²⁺ regulatory sites)	0
SR Ca²⁺ pump	120	240 (Ca²⁺ regulatory sites)	0
Parvalbumin	750	1,500 (Ca²⁺/Mg²⁺ sites)	0.15
ATP	8,000	8,000 (Ca²⁺/Mg²⁺ sites)	1.4
Furaptra	100	100 (Ca²⁺/Mg²⁺ sites)	1.59
Protein	500	500 (furaptra sites)	0

All concentrations are spatially averaged and referred to the myoplasmic water volume; except for [Ca²⁺] and [Mg²⁺], total concentrations are given. Because these concentrations are spatially averaged and because troponin and the SR Ca²⁺ pump molecules do not diffuse, the actual concentrations of troponin and the Ca²⁺ pump in the relevant compartments of the multicompartment (Fig. 2) are 2.0 and 3.0, respectively, times the values listed here. The concentration of protein applies to the four-state furaptra reaction scheme (see Fig. 1 E and Table 2 E of Baylor and Hollingworth, 2007). Free [Mg²⁺] is assumed to be constant during activity; pH (which affects the Ca²⁺ pump reaction) is assumed to be 7 and constant. The diffusion coefficients of ATP and furaptra apply to both the Ca²⁺-free and Ca²⁺-bound forms; the diffusion coefficient for parvalbumin applies to the Ca²⁺-bound, Mg²⁺-bound, and metal-free forms. From Baylor and Hollingworth (2007).

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