Effects of ryanodine and cyclopiazonic acid on skinned fibers of ventricular myocardium from neonatal and adult rats.
1. We examined the effects of ryanodine and cyclopiazonic acid (CPA) on Ca2+ release from myocardial sarcoplasmic reticulum (SR) with skinned fibers of neonatal rat ventricular myocardium. 2. Both ryanodine and CPA concentration dependently reduced the caffeine-induced tension in skinned fibers with functional SR preserved; 1 microM ryanodine and 20 microM CPA reduced the caffeine-induced tension to less than 20% of control values. 3. Both agents had no effect on the Ca(2+)-tension relation of skinned fibers without functional SR. 4. These results suggest that ryanodine and CPA inhibit Ca2+ release from the SR and Ca2+ uptake into it in neonatal myocardia. 5. Thus, less-negative inotropic effects of ryanodine and CPA on neonatal myocardia compared with those on adult myocardia (Agata et al., 1993; Tanaka and Shigenobu, 1989) could not be ascribed to lack of drug effects on the SR per se.
Takahashi
S
S
Department of Pharmacology, Toho University School of Pharmaceutical Sciences, Chiba, Japan.
Tanaka
H
H
Shigenobu
K
K
D000818:Animals; D006352:Heart Ventricles / Q000187:drug effects; D007211:Indoles / Q000494:pharmacology*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D012433:Ryanodine / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D014665:Vasodilator Agents / Q000494:pharmacology*
D007211:Indoles; D014665:Vasodilator Agents; D012433:Ryanodine; C000543:cyclopiazonic acid