Diagram showing proposed effects of cMyBP-C on the cross-bridge interaction cycle in cardiac muscle. Based on Campbell's (1997) model, strongly bound cross-bridges (predominantly A-M · ADP) cooperatively recruit cross-bridges to bind to the thin filament (represented by A). We propose that cMyBP-C is normally repressive to this mechanism by constraining cross-bridges. However, this constraint is relieved by ablation or PKA phosphorylation of cMyBP-C, resulting in increased cooperative recruitment and rates of recruitment of cross-bridges. As shown in the diagram, Ca²⁺ is required for activation of contraction (+Ca²⁺), but once initiated, the feedback mechanism shown here cooperatively increases the numbers and rate of cross-bridge binding to actin.