Effects of Caffeine and Cyclopiazonic Acid on Contractile Proteins of Adult and Newborn Ferret Cardiac Fibre

Ventricular trabeculae from adult and newborn ferret heart were chemically skinned by Triton X-100 which disrupts all cellular membranes. In newborn preparations, maximal Ca2+-activated tension was two times smaller than in adult fibres while Ca2+sensitivity was higher. Caffeine (10 m ) and cyclopiazonic acid (100 and 200μ ) increased the Ca2+sensitivity in the two groups of preparations. The caffeine effects were more pronounced in adult than in newborn fibres while the cyclopiazonic acid effects were larger in newborn preparations. In the presence of both drugs, the increase of Ca2+sensitivity was equal to the addition of the effect of each drug applied separately. These results suggest that the drugs act on two different binding sites. Consequently, care must be taken when caffeine and cyclopiazonic acid are used to study the function of the sarcoplasmic reticulum in intact or saponin-skinned fibres.