Effects of ryanodine and cyclopiazonic acid on skinned fibers of ventricular myocardium from neonatal and adult rats

• Published in: Japanese Journal of Pharmacology 1994, Vol.64 (suppl.1), p.264-264
• Main Authors: Takahashi, Sumiko, Kawada, Hiroya, Agata, Naoki, Tanaka, Hikaru, Shigenobu, Koki
• Format: Article
• Language: English
• ISSN: 0021-5198
• DOI: 10.1016/S0021-5198(19)50689-8

We previously reported that the negative inotropic potency of ryanodine (RYA) and cyclopiazonic acid (CPA) in the isolated rat ventricular myocardium were lower in the neonate than in the adult and concluded that the dependence on Ca^2+ -release from the SR increases during development (JMCC, 21：1305-1313,1989;BJP,108：571-572,1993). In the present study, we examined the effects of these agents on the caffeine-induced tension of saponin-skinned myocardial fibers from the neonate and the adult to confirm their effectiveness on the SR per se at both ages. Both RYA and CPA dose-dependently reduced the caffeine induced tension. The dose-response curves for both drugs were similar between the neonate and the adult, though slightly different; 1μM RYA and 20μM CPA reduced the caffeine-induced tension to less than 20% of control values. Further, both agents had no substantial effect on the Ca^2+ -tension relationship at both ages. Thus, the low inotropic potency of RYA and CPA on neonatal rat myocardium could not be ascribed to the ineffectiveness of these agents on Ca^2+ -release from the SR, but were most likely due to low dependence of neonatal contraction on SR function.