Length dependent potentiation and inhibition of post-rest twitch tension development in adult cat and kitten papillary muscles.

Abstract

If a rest interval is applied to a regularly stimulated cardiac muscle, the first contraction after this interval (post-rest contraction) has either a greater (post-rest potentiation) or a smaller (post-rest inhibition) developed tension than the regular contraction. Positive inotropic interventions will augment the post-rest potentiation and reduce the post-rest inhibition. We examined the effects of muscle stretching on the post-rest contraction in papillary muscles isolated from adult cats and from kittens and compared the effects with those of two typical inotropic interventions: high frequency stimulation and high calcium concentration. We found that muscle stretching augmented the post-rest potentiation and reduced the post-rest inhibition in a manner similar to the two inotropic interventions in the adult cat papillary muscle, and that these effects were consistently reversed in the kitten papillary muscle. The similarity of the effect of muscle stretching to those of the two typical inotropic interventions in either adult cat or kitten papillary muscle suggests that the effect of muscle stretching is due to an inotropic effect of muscle length change.