EFFECTS OF CAFFEINE AND CYCLOPIAZONIC ACID ON CONTRACTILE PROTEINS OFADULT AND NEWBORN FERRET CARDIAC FIBERS

Ventricular trabeculae from adult and newborn ferret heart were chemic ally skinned by Triton X-100 which disrupts all cellular. membranes. I n newborn preparations, maximal Ca2+-activated tension was two times s maller than in adult fibres while Ca2+ sensitivity was higher. Caffein e (10 mM) and cyclopiazonic acid (100 and 200 mu M) increased the Ca2 sensitivity in the two groups of preparations. The caffeine effects w ere more pronounced in adult than in newborn fibres while the cyclopia zonic acid effects were larger in newborn preparations. In the presenc e of both drugs, the increase of Ca2+ sensitivity was equal to the add ition of the effect of each drug applied separately. These results sug gest that the drugs act on two different binding sites. Consequently, care must be taken when caffeine and cyclopiazonic acid are used to st udy the function of the sarcoplasmic reticulum in intact or saponin-sk inned fibres. (C) 1996 Academic Press Limited