Frequency-dependent and proarrhythmogenic effects of FK-506 in rat ventricular cells.
FK-506, a widely used immunosuppressant, has caused a few clinical cases with QT prolongation and torsades de pointe at high blood concentration. The proarrhytmogenic potential of FK-506 was investigated in single rat ventricular cells using the whole cell clamp method to record action potentials (APs) and ionic currents. Fluorescence measurements of Ca2+ transients were performed with indo-1 AM using a multiphotonic microscope. FK-506 (25 micromol/l) hyperpolarized the resting membrane potential (RMP; -3 mV) and prolonged APs (AP duration at 90% repolarization increased by 21%) at 0.1 Hz. Prolongation was enhanced by threefold at 3.3 Hz, and early afterdepolarizations (EADs) occurred in 59% of cells. EADs were prevented by stronger intracellular Ca2+ buffering (EGTA: 10 vs. 0.5 mmol/l in the patch pipette) or replacement of extracellular Na+ by Li+, which abolishes Na+/Ca2+ exchange [Na+/Ca2+ exchanger current (INaCa)]. In indo-1-loaded cells, FK-506 generated doublets of Ca(2+) transients associated with increased diastolic Ca2+ in one-half of the cells. FK-506 reversibly decreased the L-type Ca2+ current (ICaL) by 25%, although high-frequency-dependent facilitation of ICaL persisted, and decreased three distinct K+ currents: delayed rectifier K+ current (IK; >80%), transient outward K+ current (<20%), and inward rectifier K+ current (IK1; >40%). A shift in the reversal potential of IK1 (-5 mV) accounted for RMP hyperpolarization. Numerical simulations, reproducing all experimental effects of FK-506, and the use of nifedipine showed that frequency-dependent facilitation of ICaL plays a role in the occurrence of EADs. In conclusion, the effects of FK-506 on the cardiac AP are more complex than previously reported and include inhibitions of IK1 and ICaL. Alterations in Ca2+ release and INaCa may contribute to FK-506-induced AP prolongation and EADs in addition to the permissive role of ICaL facilitation at high rates of stimulation.
Fauconnier
Jérémy
J
Physiolpatholgie Cardiovascularie, Institut National de la Santé et de la Recherche Médicale U-637, Université Montpellier 1, Montpellier, France.
Lacampagne
Alain
A
Rauzier
Jean-Michel
JM
Fontanaud
Pierre
P
Frapier
Jean-Marc
JM
Sejersted
Ole M
OM
Vassort
Guy
G
Richard
Sylvain
S
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000139:chemically induced* / Q000503:physiopathology; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000502:physiology; D004562:Electrocardiography; D005110:Extracellular Space / Q000378:metabolism; D006339:Heart Rate; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D066298:In Vitro Techniques; D008133:Long QT Syndrome / Q000139:chemically induced; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000502:physiology; D010138:Pacemaker, Artificial; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000502:physiology; D051381:Rats; D011921:Rats, Inbred WKY; D012964:Sodium / Q000378:metabolism; D016559:Tacrolimus / Q000494:pharmacology*
D020746:Calcium Channels, L-Type; D007166:Immunosuppressive Agents; D024661:Potassium Channels, Inwardly Rectifying; D012964:Sodium; D002118:Calcium; D016559:Tacrolimus