Fig. 1
From: Regulation of myocardial contraction as revealed by intracellular Ca2+ measurements using aequorin
Modified from Fig. 3 of [38] in an open access article published by Springer Nature with permission.
Structure and arrangement of cardiac thin filament proteins in the absence and presence of Ca2+. Upon Ca2+ binding to TnC, the C-terminus region of TnI dissociates from actin, allowing for Tm movement and, consequently, myosin binding to actin (indicated by arrows). Tm, tropomyosin; TnT, troponin T; TnI, troponin I; TnC, troponin C. C, COOH terminus; N, NH2 terminus. The equilibrium between the “off” state and the “on” state is a function of [Ca2+]i. H+ competes with Ca2+ for the regulatory Ca2+-binding site of TnC and thereby apparently inhibits the actomyosin interaction.