Table 2.

Estimate of maximum rate of SR Ca2+ pumping in intact fast-twitch human muscle fibers

VariableValue
Isometric ATP turnovera 2,333 μM s−1 
Fraction of ATP turnover by Ca pumpb 0.35 
ATP turnover for Ca pumping at 37°C 817 μM s−1 
ATP turnover for Ca pumping at 25°Cc 355 μM s−1 
Maximum rate of Ca uptake at 25°Cd 711 μM s−1 
a

Expressed relative to myoplasmic H2O volume; converted from 140 mM min−1 in sustained maximal contraction at 37°C (for details, see Barclay, 2017).

b

From data for type 2A human fibers (Szentesi et al., 2001) and other mammalian muscles (Barclay et al., 2007).

c

Assumed Q10 = 2 (Barclay, 2012).

d

Two Ca2+ translocated for each ATP-splitting cycle (Weber et al., 1966).

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