Figure 2. Lack of effect of MHC composition on force–pCa relationships.

Thyroidectomized myocardium (0%α-MHC, •, n= 10) and hyperthyroid myocardium (100%α -MHC, ○, n= 10) displayed similar force–pCa relationships. Data points are means ±s.e.m. Forces measured at submaximal free [Ca²⁺] were expressed relative to the maximal force obtained at pCa 4.5. The smooth lines were fitted using the Hill equation: P/P_o=[Ca²⁺]ⁿ/(kⁿ+[Ca²⁺]ⁿ)], where P is the force measured at submaximal free [Ca²⁺], P_o is the force measured at maximal free [Ca²⁺] (pCa 4.5), n_H is the Hill coefficient, and k is the Ca²⁺ concentration required for half-maximal activation.