Figure 3.

Effect of [Ca²⁺] on F₀, F_SA, and F₀+F_SA. (A) Tension response to 2.5% ML step over 1.5 ms. (B) Tension response to 1% ML length step over 0.5 ms. Data are normalized to each fiber's maximum isometric tension (F₀,_max) which was measured at pCa = 4.5 after the optimal ML was determined (see Materials and Methods). Data were fit with the Hill equation, $f=\text{a}/\left(1+{10}^{\text{b}\left(\text{x}-\text{c}\right)}\right)$. The F₀ data are the same for both A and B and are from a separate set of fibers (N = 8) than was used to determine 1% and 2.5% F_SA (N = 11). Measuring isometric tension levels and step responses versus pCa from the same fiber introduced more variability into the isometric data than measuring only isometric tension versus pCa. Values are mean ± SE.