Comparative mechanical and electrical actions of A23187 and X-537A in canine Purkinje fibers.
1. At concentrations lower than 10(-5) M, A23187 did not affect the contractile force in canine Purkinje fibers, but at 2 x 10(-5) M, decreased it significantly. 2. X-537A (10(-6) M) slightly increased the contractile force. The increase was not modified by 10(-7) M pindolol. 3. At 20 min after application both ionophores (2 x 10(-5) M) affected little or no changes in the action potential configurations, except for a marked shortening of the action potential duration. A delayed afterdepolarization and an aftercontraction occurred. 4. The electrophysiological effects were potentiated with an increase in extracellular Ca2+ and further by isoproterenol (1-3 x 10(-7) M). 5. A post-rest potentiation was depressed in the presence of these Ca2+ ionophores. 6. When the stimulation frequency was stepped up from 120 to 180 beats/min, the negative staircase of the contractile force was reversed to positive one in the presence of A23187, high Ca2+ and isoproterenol. 7. These results indicate that in canine Purkinje fibers, X-537A produces cellular Ca2+ overload, but A23187 alone does not cause it. Mechanical and electrophysiological effects induced by these ionophores are potentiated by addition of high Ca2+ and isoproterenol.
Satoh
H
H
Department of Pharmacology, Nara Medical University, Japan.
Tsuchida
K
K
Kaneko
K
K
Otomo
S
S
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects; D004285:Dogs; D004594:Electrophysiology; D066298:In Vitro Techniques; D007476:Ionophores / Q000494:pharmacology*; D007545:Isoproterenol / Q000494:pharmacology; D007832:Lasalocid / Q000494:pharmacology*; D011690:Purkinje Fibers / Q000187:drug effects*; D012849:Sinoatrial Node / Q000187:drug effects / Q000502:physiology
D015220:Calcium Channels; D007476:Ionophores; D000001:Calcimycin; D007545:Isoproterenol; D007832:Lasalocid