Effects of a monovalent ionophore, lonomycin A, on the contractile force in canine cardiac Purkinje fibers.
The mechanism for the positive inotropic effects of a monovalent ionophore, lonomycin A, in the canine cardiac Purkinje fibers was examined. Lonomycin A increased developed and resting tensions in Tyrode solution containing 1.8 mM Ca2+. The per cent increase in contractile force induced by lonomycin A was more marked in Tyrode solution with lower Ca2+ than in that with higher Ca2+. Lonomycin A did not elicit marked positive inotropic effects in modified Tyrode solution containing 40.5 mM Na+ and 0.3-0.6 mM Ca2+, compared with the positive inotropy elicited in 1.8 mM Ca2+ Tyrode solution containing 152.7 mM Na+. In 40.5 mM Na+ Tyrode solution, the concentration of Ca2+ was adjusted so that the fibers would show roughly the same contractile force before replacement of Tyrode solution containing 1.8 mM Ca2+ and 152.7 mM Na+. Ouabain remarkably augmented the positive inotropic effect induced by lonomycin A. The increased contractile force induced by lonomycin A is thus mainly due to extracellular Na+ transport into cytosol, resulting in increased [Ca2+]i via a Na-Ca exchange.
Tsuchida
K
K
Research Center, Taisho Pharmaceutical Co., Ltd., Saitama, Japan.
Kaneko
K
K
Otomo
S
S
D000818:Animals; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004285:Dogs; D066298:In Vitro Techniques; D007476:Ionophores / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects*; D009550:Nigericin / Q000031:analogs & derivatives* / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D011690:Purkinje Fibers / Q000187:drug effects*; D012964:Sodium / Q000378:metabolism; D013268:Stimulation, Chemical
D007476:Ionophores; C012410:lonomycin; D010042:Ouabain; D012964:Sodium; D009550:Nigericin