Development of difference between red and white muscles in sensitivity to Ca²⁺ in the rabbit from embryo to adult

Abstract

VARIOUS properties of the Ca²⁺-activated troponin system are different in red (slow twitch) and white (fast twitch) muscle; these differences are in molecular weight^1,2, amino acid sequences of the subunits³, Ca²⁺ binding to troponin^4,2, and biochemical measures of contraction (actomyosin ATPase activity and superprecipitation^4,7). Although the preceding differences have been investigated, no report on physiological differences in Ca²⁺-activated tension have been published. We compared the development of Ca²⁺-activated tension in an oxidative muscle fibre (soleus) and that in a glycolytic muscle fibre (adductor magnus) of the rabbit from embryo to adult. We used a technique recently developed in our laboratory⁵ for mechanically disrupting the sarcolemma of skeletal muscle fibres. We then examined the data, in view of the known biochemical differences, for possible clues to the roles that troponins have in the Ca²⁺ sensitivity of the various types of muscle.