Figure 6.

Effect of P_i on the force–pCa relationship. Skinned single fiber muscle forces measured at increasing concentrations of free Ca⁺⁺ (displayed in pCa, −log units) in the presence and absence of 30 mM P_i (A). The forces are normalized to the maximum reached at saturating pCa (4.5) and fit with the Hill plot (B). The leftward shift in the curve indicates that elevated P_i makes the fibers less sensitive to Ca⁺⁺. Figure is modified from Debold et al. (2006), reprinted with permission from the American Physiological Society.