@article {Takahashi1095, author = {S Takahashi and Y Kato and M Adachi and N Agata and H Tanaka and K Shigenobu}, title = {Effects of cyclopiazonic acid on rat myocardium: inhibition of calcium uptake into sarcoplasmic reticulum.}, volume = {272}, number = {3}, pages = {1095--1100}, year = {1995}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {The effects of cyclopiazonic acid (CPA), which is reported to inhibit Ca++ uptake into intracellular Ca++ store sites in skeletal and smooth muscles, were examined in ventricular myocardia of the adult rat. In isolated papillary muscle, 0.3 to 30 microM CPA concentration-dependently decreased the contractile force and prolonged the relaxation phase of twitch contractions. In skinned papillary muscle with functional sarcoplasmic reticulum (SR) preserved, application of CPA during the Ca++ loading period reduced the peak tension of subsequent caffeine-induced contractions. When CPA was applied during exposure to caffeine, it had no significant effect on the peak tension, but prolonged the decay of the caffeine-induced contraction. CPA had no substantial influence on the pCa-tension relationship of skinned fibers without functional SR. CPA had no substantial influence on the peak inward and steady-state membrane currents of isolated myocardial cells. These results suggest that CPA inhibits Ca uptake into SR by acting as a specific inhibitor of SR Ca(++)-ATPase in cardiac muscle as in skeletal and smooth muscles and thus provides a valuable pharmacological tool for studying myocardial excitation-contraction mechanisms.}, issn = {0022-3565}, URL = {https://jpet.aspetjournals.org/content/272/3/1095}, eprint = {https://jpet.aspetjournals.org/content/272/3/1095.full.pdf}, journal = {Journal of Pharmacology and Experimental Therapeutics} }