SARCOPLASMIC-RETICULUM FUNCTION IN NEWBORN FERRET CREMASTER SKELETAL-MUSCLES

A study of the properties of the sarcoplasmic reticulum was performed with newborn ferret cremaster muscles at two different development sta ges: at 8 and 21 days. The effects of extracellular Ca2+, caffeine and cyclopiazonic acid, a specific sarcoplasmic reticulum Ca2+-ATPase inh ibitor, were examined on intact cremaster skeletal muscles. The uptake and release of Ca2+ were explored on saponin-skinned fibres with or w ithout cyclopiazonic acid and some results obtained were compared with those obtained with adult cremaster muscle. The results have shown th at skeletal muscle sarcoplasmic reticulum of newborn animals possesses the ability to accumulate and release Ca2+. Furthermore, application of cyclopiazonic acid modified the twitch, the caffeine responses and decreased the amount of Ca2+ taken up by the sarcoplasmic reticulum in saponin-skinned fibres. In contrast to adult skeletal muscle, in newb orn cremaster muscles, the Ca2+ dependence of the twitch suggests that the Ca2+ influx at the sarcolemma level was mainly involved in the ac tivation of the contraction. Furthermore, the results obtained in the presence of cyclopiazonic acid were in favour, as in adult muscle, of a participation of the sarcoplasmic reticulum in the relaxation proces s.