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.
Physiolpatholgie Cardiovascularie, Institut National de la Santé et de la Recherche Médicale U-637, Université Montpellier 1, Montpellier, France.
Jérémy
J
Fauconnier
Alain
A
Lacampagne
Jean-Michel
JM
Rauzier
Pierre
P
Fontanaud
Jean-Marc
JM
Frapier
Ole M
OM
Sejersted
Guy
G
Vassort
Sylvain
S
Richard
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