The Ca ²⁺ sensitivities of force and the rate of force redevelopment in mammalian skinned myocardium. (A–C) Relative force–pCa (filled circle) and relative ktr–pCa (empty circle) relationships were determined in permeabilized myocardial preparations isolated from murine ventricular myocardium (A), porcine atrial myocardium (B), and porcine ventricular myocardium (C). Data points are means and the error bars are the SEM.