Fig. 3. Illustration of passive tension in striated muscle showing the effect of titin isoform expression (N2A, N2BA and/or combination thereof as indicated by shaded area between lines) and modulation of titin by Ca²⁺ binding or phosphorylation on passive tension in mammalian cardiac muscle. Redrawn from Granzier and Labeit (Granzier and Labeit, 2004). Passive tension data measured from isolated rainbow trout ventricular myocytes [replotted from Shiels et al. (Shiels et al., 2006)] showing the low level of passive force generated by fish heart, even at long sarcomere lengths.