title: On the ionic mechanism of cyproheptadine-induced bradycardia in a rabbit sinoatrial node preparation.
abstract: The effects of cyproheptadine (0.1-10 microM) on the membrane potentials and currents of rabbit sinoatrial node were examined with the double-microelectrode voltage clamp technique. Cyproheptadine reduced the heart rate, maximum rate of depolarization and action potential amplitude. It also decreased the slope of phase 4 depolarization. On the current systems, cyproheptadine decreased the slow inward current (Isi), the time-dependent potassium outward current (Ik) and the hyperpolarization-activated current (Ih). The reduction of Isi was the major effect. Furthermore, Isi was progressively decreased by repetitive membrane depolarization during administration of cyproheptadine, an effect suggestive of frequency-dependent block of Isi. These electrophysiological observations indicate that cyproheptadine has a calcium antagonistic property, and additionally, decreases Ik and Ih in rabbit sinoatrial node.
authors: 1st Department of Internal Medicine, Yonago, Japan.
authors: H
authors: H
authors: Kotake
authors: M
authors: M
authors: Saitoh
authors: K
authors: K
authors: Ogino
authors: S
authors: S
authors: Hirai
authors: S
authors: S
authors: Matsuoka
authors: J
authors: J
authors: Hasegawa
authors: H
authors: H
authors: Mashiba
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D003533:Cyproheptadine / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects*; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D011817:Rabbits; D012849:Sinoatrial Node / Q000187:drug effects / Q000502:physiology*
chemical_list: D003533:Cyproheptadine