title: Quinidine enhances intracellular Ca2+ accumulation during rapid stimulation.
abstract: 1. The quinidine-induced modification of intracellular Ca2+ concentration ([Ca2+]i) was studied in guinea-pig myocardium using fura-2. Quinidine reduced the systolic fluorescence signal level for [Ca2+]i and enhanced the end-diastolic signal level during a stimulation train. 2. The diastolic decay of [Ca2+]i fitted 2 exponential curves. Quinidine distorted the stimulation frequency-dependent acceleration of rapid [Ca2+]i decay, and prolonged the mean time constant of rapid decay after 2 Hz stimulation, from 154.4 to 205.3 msec (20 microM), and to 259.7 msec (60 microM quinidine). The time constant of slow recovery from [Ca2+]i accumulation after the stimulation train was not affected by stimulation frequency, or by quinidine, or caffeine. 3. These results suggest that quinidine modulates [Ca2+]i via a balance between the slowing of rapid [Ca2+]i decay and the reduction of the systolic [Ca2+]i. This effect may contribute to the anti-arrhythmic and pro-arrhythmic effects exerted by quinidine in some conditions.
authors.affiliation: Department of Internal Medicine, Faculty of Medicine, Tottori University, Yonago, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Hasegawa
authors.forename: M
authors.initials: M
authors.lastname: Tsuboi
authors.forename: K
authors.initials: K
authors.lastname: Narasaki
authors.forename: S
authors.initials: S
authors.lastname: Hirai
authors.forename: T
authors.initials: T
authors.lastname: Nawada
authors.forename: H
authors.initials: H
authors.lastname: Kotake
authors.forename: H
authors.initials: H
authors.lastname: Mashiba
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004558:Electric Stimulation; D016257:Fura-2; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D011802:Quinidine / Q000494:pharmacology*; D013599:Systole / Q000502:physiology
chemical_list: D002110:Caffeine; D011802:Quinidine; D002118:Calcium; D016257:Fura-2