title: Analysis of moricizine block of sodium current in isolated guinea-pig atrial myocytes. Atrioventricular difference of moricizine block.
abstract: The effects of moricizine on Na+ channel currents (INa) were investigated in guinea-pig atrial myocytes and its effects on INa in ventricular myocytes and on cloned hH1 current were compared using the whole-cell, patch-clamp technique. Moricizine induced the tonic block of INa with the apparent dissociation constant (Kd,app) of 6.3 microM at -100 mV and 99.3 microM at -140 mV. Moricizine at 30 microM shifted the h infinity curve to the hyperpolarizing direction by 8.6 +/- 2.4 mV. Moricizine also produced the phasic block of INa, which was enhanced with the increase in the duration of train pulses, and was more prominent with a holding potential (HP) of -100 mV than with an HP of -140 mV. The onset block of INa induced by moricizine during depolarization to -20 mV was continuously increased with increasing the pulse duration, and was enhanced at the less negative HP. The slower component of recovery of the moricizine-induced INa block was relatively slow, with a time constant of 4.2 +/- 2.0 s at -100 mV and 3.0 +/- 1.2 s at -140 mV. Since moricizine induced the tonic block of ventricular INa with Kd,app of 3.1 +/- 0.8 microM at HP = -100 mV and 30.2 +/- 6.8 microM at HP = -140 mV, and cloned hH1 with Kd,app of 3.0 +/- 0.5 microM at HP = -100 mV and 22.0 +/- 3.2 microM at HP = -140 mV, respectively, either ventricular INa or cloned hH1 had significantly higher sensitivity to moricizine than atrial INa. The h infinity curve of ventricular INa was shifted by 10.5 +/- 3.5 mV by 3 microM moricizine and that of hH1 was shifted by 5.0 +/- 2.3 mV by 30 microM moricizine. From the modulated receptor theory, we have estimated the dissociation constants for the resting and inactivated state to be 99.3 and 1.2 microM in atrial myocytes, 30 and 0.17 microM in ventricular myocytes, and 22 and 0.2 microM in cloned hH1, respectively. We conclude that moricizine has a higher affinity for the inactivated Na+ channel than for the resting state channel in atrial myocytes, and moricizine showed the significant atrioventricular difference of moricizine block on INa. Moricizine would exert an antiarrhythmic action on atrial myocytes, as well as on ventricular myocytes, by blocking Na+ channels with a high affinity to the inactivated state and a slow dissociation kinetics.
authors.affiliation: Division of Cardiology, Department of Medicine, Tottori University Faculty of Medicine, Nishimachi 36-1, Yonago, 683, Japan.
authors.forename: Gias U
authors.initials: GU
authors.lastname: Ahmmed
authors.forename: Ichiro
authors.initials: I
authors.lastname: Hisatome
authors.forename: Yasutaka
authors.initials: Y
authors.lastname: Kurata
authors.forename: Naomasa
authors.initials: N
authors.lastname: Makita
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Tanaka
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Okamura
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Sonoyama
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Furuse
authors.forename: Masaru
authors.initials: M
authors.lastname: Kato
authors.forename: Yasutaka
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Ogura
authors.forename: Masaki
authors.initials: M
authors.lastname: Shimoyama
authors.forename: Junichiro
authors.initials: J
authors.lastname: Miake
authors.forename: Norihito
authors.initials: N
authors.lastname: Sasaki
authors.forename: Kazuhide
authors.initials: K
authors.lastname: Ogino
authors.forename: Osamu
authors.initials: O
authors.lastname: Igawa
authors.forename: Akio
authors.initials: A
authors.lastname: Yoshida
authors.forename: Chiak
authors.initials: C
authors.lastname: Shigemasa
mesh_terms: D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D002478:Cells, Cultured; D006168:Guinea Pigs; D006325:Heart Atria / Q000166:cytology; D006352:Heart Ventricles / Q000166:cytology; D007700:Kinetics; D008955:Models, Cardiovascular; D016293:Moricizine / Q000494:pharmacology*; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects* / Q000502:physiology
chemical_list: D000889:Anti-Arrhythmia Agents; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D016293:Moricizine