Fig. 4.

The interplay between the thick and thin filaments mediated by cMyBP-C. The relaxed state is represented as a continuum of thick filament and thin filament states, which are modulated by phosphorylation and/or force. In a completely relaxed condition very few C-zone heads are likely to be activated, at the other end of the spectrum with RLC, cMyBP-C phosphorylation, and force the number of heads ready for generating tension is maximized. Interestingly, even though phosphorylation of cMyBP-C releases heads from the thick filament, it prevents cMyBP-C interacting with the thin filament. The acute stage of activation, mediated by calcium binding to the thin filament, results in cross-bridge attachment and now cMyBP-C can reveal its second, modulatory role on contraction. The complexity of this process is grossly underestimated in this diagram, however the questions necessary to understand this process are revealed