The site concentrations are spatially averaged and referred to the myoplasmic water volume (Baylor et al., 1983). The fast-twitch model ignores the 240-µM troponin-nonspecific sites (Ca²⁺/Mg²⁺ sites) because their buffering effect is small compared with the sites on parvalbumin, which are present in the fast-twitch model at a large concentration. Other myoplasmic Ca²⁺-binding sites, such as those on inorganic phosphate, calmodulin, calpain, calcineurin, sorcin, annexin, S100A, the plasmalemma Ca²⁺ pump, and the Na⁺/Ca²⁺ exchanger, have been ignored because their concentrations are small relative to those of the major buffers listed in the table. The kinetic parameters for the sites at 16°C are given in Baylor and Hollingworth (2007) and Hollingworth et al. (2012). Both models assume that free [Ca²⁺] at rest is 0.05 µM and that free [Mg²⁺] is 1 mM and constant.

van Eerd and Takahashi, 1976; Potter et al., 1977; and Robertson et al., 1981.

Kushmerick et al., 1992, and Racay et al., 2006.

Heizmann et al., 1982, and Leberer and Pette, 1986.

Robertson et al., 1981.

Ferguson and Franzini-Armstrong, 1988.

Baylor and Hollingworth, 2007, and Hollingworth et al., 2012.