The correlation of acto-myosin ATPase rate with tension redevelopment kinetics (k(tr)) was determined during Ca+2-activated contractions of demembranated rabbit psoas muscle fibers; the ATPase rate was either increased or decreased relative to control by substitution of ATP (5.0 mM) with 2-deoxy-ATP (dATP) (5.0 mM) or by lowering [ATP] to 0.5 mM, respectively. The activation dependence of k(tr) and unloaded shortening velocity (V(u)) was measured with each substrate. With 5.0 mM ATP, V(u) depended linearly on tension (P), whereas k(tr) exhibited a nonlinear dependence on P1 being relatively independent of P at submaximum levels and rising steeply at P > 0.6-0.7 of maximum tension (P(o)). With dATP, V(u) was 25% greater than control at P(o) and was elevated at all P > 0.15P(o), whereas P(o) was unchanged. Furthermore, the Ca+2 sensitivity of both k(tr) and P increased, such that the dependence of k(tr) on P was not significantly different from control, despite an elevation of V(u) and maximal k(tr). In contrast, lowering [ATP] caused a slight (8%) elevation of P(o), no change in the Ca+2 sensitivity of P, and a decrease in V(u) at all P. Moreover, k(tr) was decreased relative to control at P > 0.75P(o), but was elevated at P < 0.75P(o). These data demonstrate that the cross-bridge cycling rate dominates k(tr) at maximum but not submaximum levels of Ca2+ activation.
Regnier, M., Martyn, D. A., & Chase, P. B. (1998). Calcium regulation of tension redevelopment kinetics with 2-deoxy-ATP or low [ATP] in rabbit skeletal muscle. Biophysical Journal, 74(4), 2005–2015. https://doi.org/10.1016/S0006-3495(98)77907-X