The study demonstrates that Vmax and Pmax in rabbit papillary muscles are governed by a common control mechanism in excitation-contraction coupling that is altered by pacing frequency.
Abstract The time course of the active state, the force‐velocity relationship and the series compliance of rabbit papillary muscles were studied at different inotropic states produced by altered pacing of the muscles within the range 18 to 72 stimulations per minute. The inotropic intervention produced a shift of the force‐velocity curve, without markedly changing the shape of the curve, suggesting that V max , the capacity to produce motion, and P max the capacity to produce tension, were affected to the same degree. Intensification of the active state in response to an increase in stimulation frequency was associated with a steeper rise of the active state and an earlier attainment of maximum. The series compliance was unaffected by the inotropic intervention. The results are taken as evidence (1) that the two parameters of the active state, V max and P max , are governed by a common control mechanism in the excitation‐contraction coupling and (2) that the inotropic effect is due to altered kinetics of this control function. The nature of the mechanism governing the active state is discussed in relation to the slicling‐filament theory of muscular contraction.
Edman et al. (Thu,) studied this question.