tacrolimus and Arrhythmias--Cardiac

The heart contraction is controlled by the Ca2+-induced Ca2+ release (CICR) between L-type Ca2+ channels and ryanodine receptors (RyRs). The FK506-binding protein FKBP12.6 binds to RyR subunits, but its role in stabilizing RyR function has been debated for long. Recent reports of high-resolution RyR structure show that the HD2 domain that binds to the SPRY2 domain of neighbouring subunit in FKBP-bound RyR1 is detached and invisible in FKBP-null RyR2. The present study was to test the consequence of FKBP12.6 absence on the in situ activation of RyR2.. Using whole-cell patch-clamp combined with confocal imaging, we applied a near threshold depolarization to activate a very small fraction of LCCs, which in turn activated RyR Ca2+ sparks stochastically. FKBP12.6-knockout and FK506/rapamycin treatments increased spark frequency and LCC-RyR coupling fidelity without altering LCC open probability. Neither FK506 nor rapamycin further altered LCC-RyR coupling fidelity in FKBP12.6-knockout cells. In loose-seal patch-clamp experiments, the LCC-RyR signalling kinetics, indexed by the delay for a LCC sparklet to trigger a RyR spark, was accelerated after FKBP12.6 knockout and FK506/rapamycin treatments. These results demonstrated that RyRs became more sensitive to Ca2+ triggers without FKBP12.6. Isoproterenol (1 μM) further accelerated the LCC-RyR signalling in FKBP12.6-knockout cells. The synergistic sensitization of RyRs by catecholaminergic signalling and FKBP12.6 dysfunction destabilized the CICR system, leading to chaotic Ca2+ waves and ventricular arrhythmias.. FKBP12.6 keeps the RyRs from over-sensitization, stabilizes the potentially regenerative CICR system, and thus may suppress the life-threatening arrhythmogenesis.

Topics: Animals; Arrhythmias, Cardiac; Calcium Channels, L-Type; Calcium Signaling; Genotype; Isoproterenol; Kinetics; Male; Membrane Potentials; Mice, Knockout; Microscopy, Confocal; Models, Molecular; Myocytes, Cardiac; Patch-Clamp Techniques; Phenotype; Protein Binding; Protein Interaction Domains and Motifs; Receptor Cross-Talk; Ryanodine Receptor Calcium Release Channel; Sirolimus; Stochastic Processes; Tacrolimus; Tacrolimus Binding Proteins

Sudden cardiac deaths due to arrhythmias are thought to be an important cause of mortality in patients with renal transplants. Exposure to immunosuppressive drugs may lead to QT or PR interval abnormalities which may consequently cause arrhythmias. Our study investigated the long term impact of four different immunosuppressive drugs on PR and corrected QT intervals (QTc) in renal transplant patients. The study population consisted of 98 kidney transplant recipients. Study patients were receiving immunosuppressive management with tacrolimus, cyclosporine A, everolimus or azathioprine according to the local protocols. QTc and PR intervals obtained from the most recent post-transplant electrocardiograms were compared with the pre-transplant intervals dated before the transplantation procedure.. Post-transplant QTc intervals had prolonged significantly in comparison to the pre-transplant QTc intervals in all groups. However, there were no significant differences between the immunosuppressive agents with regard to post-transplant QTc interval prolongation (p > 0.05). There were no significant differences between the groups with regard to the pre and post-transplant PR interval changes (p > 0.05).. QT interval prolongation, a marker of risk for arrhythmias and sudden death, is highly prevalent among kidney transplant patients receiving different classes of immunosuppressive drugs.

Topics: Adult; Arrhythmias, Cardiac; Azathioprine; Cyclosporine; Death, Sudden, Cardiac; Disease Progression; Electrocardiography; Everolimus; Female; Humans; Immunosuppressive Agents; Kidney Failure, Chronic; Kidney Transplantation; Male; Middle Aged; Tacrolimus

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.

Topics: Action Potentials; Animals; Arrhythmias, Cardiac; Calcium; Calcium Channels, L-Type; Electrocardiography; Extracellular Space; Heart Rate; Immunosuppressive Agents; In Vitro Techniques; Long QT Syndrome; Myocytes, Cardiac; Pacemaker, Artificial; Patch-Clamp Techniques; Potassium Channels, Inwardly Rectifying; Rats; Rats, Inbred WKY; Sodium; Tacrolimus

We investigated the inward rectifier potassium current (I(K1)), which can be blocked by intracellular Ca(2+), in heart failure (HF).. We used the whole-cell patch-clamp technique to record I(K1) from single rat ventricular myocytes in voltage-clamp conditions. Fluorescence measurements of diastolic Ca(2+) were performed with Indo-1 AM. HF was examined 8 weeks after myocardial infarction (coronary artery ligation).. I(K1) was reduced and diastolic Ca(2+) was increased in HF cells. The reduction of I(K1) was attenuated when EGTA was elevated from 0.5 to 10 mM in the patch pipette and prevented with high BAPTA (20 mM). Ryanodine (100 nM) and FK506 (10 microM), both of which promote spontaneous SR Ca(2+) release from ryanodine receptor (RyR2) during diastole, reproduced the effect of HF on I(K1) in normal cells but had no effect in HF cells. The effects of ryanodine and FK506 were not additive and were prevented by BAPTA. Rapamycin (10 microM), which removes FKBP binding proteins from RyR2 with no effect on calcineurin, mimicked the effect of FK506 on I(K1). Cyclosporine A (10 microM), which inhibits calcineurin via cyclophilins, had no effect. In both HF cells and normal cells treated by FK506, the protein kinase C (PKC) inhibitor staurosporine totally restored the inward component of I(K1), but only partially restored its outward component at potentials corresponding to the late repolarizing phase of the action potential (-80 to -40 mV).. I(K1) is reduced by elevated diastolic Ca(2+)in HF, which involves in parallel PKC-dependent and PKC-independent mechanisms. This regulation provides a novel paradigm for Ca(2+)-dependent modulation of membrane potential in HF. Since enhanced RyR2-mediated Ca(2+)release also reduces I(K1), this paradigm might be relevant for arrhythmias related to acquired or inherited RyR2 dysfunction.

Topics: Action Potentials; Animals; Arrhythmias, Cardiac; Calcium; Depression, Chemical; Egtazic Acid; Heart Failure; Immunosuppressive Agents; Male; Myocardial Infarction; Myocardium; Patch-Clamp Techniques; Potassium Channels, Inwardly Rectifying; Protein Kinase C; Rats; Rats, Wistar; Ryanodine; Ryanodine Receptor Calcium Release Channel; Sirolimus; Staurosporine; Tacrolimus

The use of immunosuppressant agents is mandatory in the long-term management of transplant recipients. Herein, we report a case of near fatal cardiac arrhythmia related to the use of intravenous tacrolimus in a 35-year-old woman undergoing renal transplantation.. The patient had no previous history of cardiac disease, but an initial electrocardiogram demonstrated slightly prolonged QT and QTc intervals and normal sinus rhythm. Postsurgical immunosuppression included intravenous tacrolimus and methylprednisolone. During intravenous tacrolimus infusion, marked QT prolongation occurred. The patient suffered recurrent runs of torsade de pointes, refractory to aggressive medical management and requiring numerous defibrillations. Rapid atrial pacing eventually controlled the arrhythmia.. We note not only a temporal association, but also a direct linear relationship, between this arrhythmia and blood tacrolimus levels.. We believe this case presents a little recognized hazard associated with the use of intravenous tacrolimus and points to the need for careful predrug screening for QT prolongation. Tacrolimus has been shown to effect intracellular calcium and to prolong the action potential duration experimentally. This suggests that an increase in the intracellular calcium may underlie torsades de pointes associated with intravenous tacrolimus.

Topics: Adult; Arrhythmias, Cardiac; Electrocardiography; Female; Humans; Immunosuppressive Agents; Kidney Transplantation; Tacrolimus

Topics: Arrhythmias, Cardiac; Child; Cyclosporine; Drug Therapy, Combination; Female; Heart Transplantation; Humans; Immunosuppressive Agents; Magnesium Deficiency; Tacrolimus