Quinidine enhances intracellular Ca2+ accumulation during rapid stimulation.
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.
Hasegawa
J
J
Department of Internal Medicine, Faculty of Medicine, Tottori University, Yonago, Japan.
Tsuboi
M
M
Narasaki
K
K
Hirai
S
S
Nawada
T
T
Kotake
H
H
Mashiba
H
H
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
D002110:Caffeine; D011802:Quinidine; D002118:Calcium; D016257:Fura-2