Sevoflurane Inhibition of the Slowly Activating Delayed Rectifier K+ Current in Guinea Pig Ventricular Cells

Prediction of anesthetic torsadogenicity using a human ventricular cell model

This simulation study was designed to predict the torsadogenicity of sevoflurane and propofol in healthy control, as well as type 1 and type 2 long QT syndrome (LQT1 and LQT2, respectively), using the O'Hara-Rudy dynamic model. LQT1 and LQT2 models were simulated by decreasing the conductances of slowly and rapidly activating delayed rectifier K+ currents (IKs and IKr, respectively) by 50%, respectively. Action potential duration at 50% repolarization level (APD50) and diastolic intracellular Ca2+ concentration were measured in epicardial cell during administration of sevoflurane (1 ~ 5%) and propofol (1 ~ 10 μM). Torsadogenicity can be predicted from the relationship between APD50 and diastolic intracellular Ca2+ concentration, which is classified by the decision boundary. Whereas the relationships in control and LQT1 models were distributed on nontorsadogenic side in the presence of sevoflurane at all tested concentrations, those in LQT2 models were shifted to torsadogenic side by concentrations of ≥ 2%. In all three models, propofol shifted the relationships in a direction away from the decision boundary on nontorsadogenic side. Our findings suggest that sevoflurane, but not propofol, exerts torsadogenicity in patients with reduced IKr, such as LQT2 patients. Caution should be paid to the occurrence of arrhythmia during sevoflurane anesthesia in patients with reduced IKr.

Huffing and twist: Fatal Torsade de pointes associated with Tetrafluoroethane Inhalation and amphetamine use

Many volatile chemicals inhaled for a recreational high have a chemical structure similar to chloroform and may lead to Ikr blockade and subsequent torsades de pointes. This is one potential mechanism of action for huffing-associated sudden death.

In vivo analysis of concentration-dependent effects of halothane or isoflurane inhalation on the electrocardiographic and hemodynamic variables in dogs

We assessed concentration-dependent effects of halothane or isoflurane inhalation on the electrocardiographic and hemodynamic variables using a cross-over design in intact beagle dogs (n = 4). Elevation of inhaled halothane from 1.0% to 2.0% or isoflurane from 1.5% to 2.5% decreased the mean blood pressure and prolonged the QRS width without significantly altering the heart rate, PR interval or QT interval. However, the observed changes disappeared after regressions of both anesthetic conditions to their initial settings. These results indicate that hypotension-induced, reflex-mediated increase of sympathetic tone may have counterbalanced the direct negative chronotropic, dromotropic and repolarization slowing effects of the anesthetics.

In vivo comparison of dl-sotalol-induced electrocardiographic responses among halothane anesthesia, isoflurane anesthesia with nitrous oxide, and conscious state

We compared dl-sotalol-induced electrocardiographic responses in intact dogs using a repeated-measures design among 1% halothane anesthesia, 1.5% isoflurane anesthesia with nitrous oxide (N₂O), and conscious state to clarify influences of the anesthetics (n = 4). Basal PR interval was longer in halothane than either in isoflurane with N₂O or in conscious state, reflecting sympathetic nerve suppression for the atrioventricular node by halothane. Both anesthetics exhibited longer basal QRS width than conscious state, suggesting their ventricular I_Na inhibition. Also, both anesthetics showed longer basal QT interval, QTcF and T_peak-T_end than conscious state, indicating their ventricular I_Kr inhibition. Meanwhile, dl-sotalol prolonged PR interval similarly in isoflurane with N₂O and in conscious state, which was less great in halothane, suggesting further sympathetic nerve suppression for the atrioventricular node might be limited in halothane. dl-Sotalol prolonged QT interval and QTcF >3 times greater in either of the anesthetics than in conscious state; moreover, dl-sotalol prolonged T_peak-T_end similarly in both anesthetics, but hardly altered it in conscious state; indicating isoflurane with N₂O as well as halothane may have reduced the repolarization reserve to increase the sensitivity of ventricle toward I_Kr suppression. Thus, isoflurane with nitrous oxide could be useful for in vivo I_Kr assay like halothane.

Interaction of propofol with voltage-gated human Kv1.5 channel through specific amino acids within the pore region

The intravenous anesthetic propofol affects the function of a diversity of ligand-gated and voltage-gated ion channels. However, there is little information as to whether propofol directly interacts with voltage-gated ion channel proteins to modulate their functions. The Kv1.5 channel is activated by membrane depolarization during action potentials and contributes to atrial repolarization in the human heart. This study was undertaken to examine the effect of propofol on voltage-gated human Kv1.5 (hKv1.5) channel and to elucidate the underlying molecular determinants. Site-directed mutagenesis was carried out through six amino acids that reside within the pore domain of hKv1.5 channel. Whole-cell patch-clamp technique was used to record membrane currents through the wild type and mutant hKv1.5 channels heterologously expressed in Chinese hamster ovary cells. Propofol (≥5 μM) reversibly and concentration-dependently (IC50 of 49.3±9.4 μM; n=6) blocked hKv1.5 current. Propofol-induced block of hKv1.5 current gradually progressed during depolarizing voltage-clamp steps and was enhanced by higher frequency of activation, consistent with a preferential block of the channels in their open state. The degree of current block by propofol was significantly attenuated in T480A, I502A, I508A and V516A, but not in H463C and L510A mutants of hKv1.5 channel. Thus, several amino acids near the selectivity filter (Thr480) or within S6 (Ile502, Ile508 and Val516) are found to be critically involved in the blocking action of propofol. This study provides the first evidence suggesting that direct interaction with specific amino acids underlies the blocking action of propofol on voltage-gated hKv1.5 channel.

Enhanced effects of isoflurane on the long QT syndrome 1-associated A341V mutant

BACKGROUND

The impact of volatile anesthetics on patients with inherited long QT syndrome (LQTS) is not well understood. This is further complicated by the different genotypes underlying LQTS. No studies have reported on the direct effects of volatile anesthetics on specific LQTS-associated mutations. We investigated the effects of isoflurane on a common LQTS type 1 mutation, A341V, with an unusually severe phenotype.

METHODS

Whole cell potassium currents (IKs) were recorded from HEK293 and HL-1 cells transiently expressing/coexpressing wild-type KCNQ1 (α-subunit), mutant KCNQ1, wild-type KCNE1 (β-subunit), and fusion KCNQ1 + KCNE1. Current was monitored in the absence and presence of clinically relevant concentration of isoflurane (0.54 ± 0.05 mM, 1.14 vol %). Computer simulations determined the resulting impact on the cardiac action potential.

RESULTS

Isoflurane had significantly greater inhibitory effect on A341V + KCNE1 (62.2 ± 3.4%, n = 8) than on wild-type KCNQ1 + KCNE1 (40.7 ± 4.5%; n = 9) in transfected HEK293 cells. Under heterozygous conditions, isoflurane inhibited A341V + KCNQ1 + KCNE1 by 65.2 ± 3.0% (n = 13) and wild-type KCNQ1 + KCNE1 (2:1 ratio) by 32.0 ± 4.5% (n = 11). A341V exerted a dominant negative effect on IKs. Similar differential effects of isoflurane were also observed in experiments using the cardiac HL-1 cells. Mutations of the neighboring F340 residue significantly attenuated the effects of isoflurane, and fusion proteins revealed the modulatory effect of KCNE1. Action potential simulations revealed a stimulation frequency-dependent effect of A341V.

CONCLUSIONS

The LQTS-associated A341V mutation rendered the IKs channel more sensitive to the inhibitory effects of isoflurane compared to wild-type IKs in transfected cell lines; F340 is a key residue for anesthetic action.

Ionic mechanisms underlying the negative chronotropic action of propofol on sinoatrial node automaticity in guinea pig heart

BACKGROUND AND PURPOSE

Propofol is a widely used intravenous anaesthetic agent, but has undesirable cardiac side effects, including bradyarrhythmia and its severe form asystole. This study examined the ionic and cellular mechanisms underlying propofol-induced bradycardia.

EXPERIMENTAL APPROACH

Sinoatrial node cells, isolated from guinea pig hearts, were current- and voltage-clamped to record action potentials and major ionic currents involved in their spontaneous activity, such as the hyperpolarization-activated cation current (If ), T-type and L-type Ca(2+) currents (ICa,T and ICa,L , respectively) and the rapidly and slowly activating delayed rectifier K(+) currents (IKr and IK s , respectively). ECGs were recorded from Langendorff-perfused, isolated guinea pig hearts.

KEY RESULTS

Propofol (≥5 μM) reversibly decreased the firing rate of spontaneous action potentials and their diastolic depolarization rate. Propofol impaired If activation by shifting the voltage-dependent activation to more hyperpolarized potentials (≥1 μM), slowing the activation kinetics (≥3 μM) and decreasing the maximal conductance (≥10 μM). Propofol decreased ICa,T (≥3 μM) and ICa,L (≥1 μM). Propofol suppressed IKs (≥3 μM), but had a minimal effect on IKr . Furthermore, propofol (≥5 μM) decreased heart rates in Langendorff-perfused hearts. The sinoatrial node cell model reasonably well reproduced the negative chronotropic action of propofol.

CONCLUSIONS AND IMPLICATIONS

Micromolar concentrations of propofol suppressed the slow diastolic depolarization and firing rate of sinoatrial node action potentials by impairing If activation and reducing ICa,T , ICa,L and IKs . These observations suggest that the direct inhibitory effect of propofol on sinoatrial node automaticity, mediated via multiple channel inhibition, underlies the propofol-induced bradycardia observed in clinical settings.

Direct negative chronotropic action of desflurane on sinoatrial node pacemaker activity in the guinea pig heart

BACKGROUND

Desflurane inhalation is associated with sympathetic activation and concomitant increase in heart rate in humans and experimental animals. There is, however, little information concerning the direct effects of desflurane on electrical activity of sinoatrial node pacemaker cells that determines the intrinsic heart rate.

METHODS

Whole-cell patch-clamp experiments were conducted on guinea pig sinoatrial node pacemaker cells to record spontaneous action potentials and ionic currents contributing to sinoatrial node automaticity, namely, hyperpolarization-activated cation current (If), T-type and L-type Ca currents (ICa,T and ICa,L, respectively), Na/Ca exchange current (INCX), and rapidly and slowly activating delayed rectifier K currents (IKr and IKs, respectively). Electrocardiograms were recorded from ex vivo Langendorff-perfused hearts and in vivo hearts.

RESULTS

Desflurane at 6 and 12% decreased spontaneous firing rate of sinoatrial node action potentials by 15.9% (n = 11) and 27.6% (n = 10), respectively, which was associated with 20.4% and 42.5% reductions in diastolic depolarization rate, respectively. Desflurane inhibited If, ICa,T, ICa,L, INCX, and IKs but had little effect on IKr. The negative chronotropic action of desflurane was reasonably well reproduced in sinoatrial node computer model. Desflurane reduced the heart rate in Langendorff-perfused hearts. High concentration (12%) of desflurane inhalation was associated with transient tachycardia, which was totally abolished by pretreatment with the β-adrenergic blocker propranolol.

CONCLUSIONS

Desflurane has a direct negative chronotropic action on sinoatrial node pacemaking activity, which is mediated by its inhibitory action on multiple ionic currents. This direct inhibitory action of desflurane on sinoatrial node automaticity seems to be counteracted by sympathetic activation associated with desflurane inhalation in vivo.

The effect of sevoflurane and ondansetron on QT interval and transmural dispersion of repolarization in children

BACKGROUND

This study evaluated the prolongation of QT interval by the combination of sevoflurane and ondansetron in pediatric patients. Additionally, transmural dispersion of repolarization as interval between the peak and end of the T wave (Tp-e) and Tp-e/QT ratio was also measured to assess the risk of ventricular arrhythmia.

METHODS

The 3-lead electrocardiography (ECG) in lead II was sampled at three stages: at preinduction, just before (Sevo alone) and finally, after administration of ondansetron (Sevo+Ondansetron) in 41 children aged from 3 to 12 years. The QT interval was corrected for heart rate using Bazett's formula. And, Tp-e interval was obtained, and Tp-e/QT ratio was calculated. For analysis of the changes of parameters, a repeated-measures analysis of variance was used to identify significant differences in QTc, Tp-e interval and Tp-e/QT ratio at the three epochs.

RESULTS

The mean QTc at preinduction period was 413.8 (20.8) ms. The mean Sevo alone and Sevo+Ondansetron QTcs were 432.5 (28.1) and 439.2 (27.6) ms, and the differences in QTc prolongation between stages were all significant (P < 0.01). Ondansetron increased Tp-e interval significantly; however, Tp-e/QT ratio was not different among three stages. There were no ECG abnormalities such as atrial or ventricular arrhythmia and T-wave abnormality in any patient.

CONCLUSIONS

Sevoflurane prolongs the QTc interval and its combination with ondansetron further increased this effect in children. However, the dispersion of ventricular repolarization was not significantly affected, and there were no adverse events such as ventricular arrhythmia in this study. The combination of sevoflurane and ondansetron may be clinically safe, but careful ECG monitoring is still advisable.

Perioperative doses of ondansetron or dolasetron do not lengthen the QT interval

OBJECTIVE

To test the primary hypothesis that ondansetron or dolasetron extends the rate-corrected QT electrocardiographic interval (QTc) greater than 60 milliseconds or increases the fraction of patients with QTc greater than 500 milliseconds in patients having noncardiac surgery, and the secondary hypothesis that QTc prolongation is worse in diabetic patients.

PATIENTS AND METHODS

We extracted data from the Cleveland Clinic's Perioperative Health Documentation System between March 25, 2006, and September 30, 2010, and additional perioperative medications from Cleveland Clinic pharmacy's Epic Cost of Goods Sold (COGS) system. We searched for patients who had a preoperative electrocardiogram within 1 month of surgery and postoperatively within 2 hours. We excluded patients given an antiemetic drug other than ondansetron or dolasetron perioperatively, and those given amiodarone.

RESULTS

A total of 1429 patients given serotonin-3 receptor (5HT3R) antagonists and 1022 controls met the enrollment criteria. Seventeen percent of patients given 5HT3R antagonists (n=242) and 22% of controls (n=220) had postoperative QTc exceeding 500 milliseconds. Mean ± SD presurgical and postsurgical QTc, respectively, were 438±37 milliseconds and 464±41 milliseconds for 5HT3R antagonist patients and 443±40 milliseconds and 469±47 milliseconds for control patients. Univariable mean ± SD perioperative increases in QTc were 26±39 and 26±48 milliseconds in the 2 groups. After adjusting for confounding variables, there were no differences in the mean increase in QTc in patients who were and were not given 5HT3R antagonists: -0.1 milliseconds (97.5% CI, -5.2 to 5.0 milliseconds; multivariable P=.97). The QTc was prolonged, but not significantly, in diabetic patients given 5HT3R antagonists (P=.16).

CONCLUSIONS

The average QTc prolongation from baseline was only 6%. Perioperative use of ondansetron or dolasetron was not associated with extended QT prolongation, and these results did not vary by diabetic status. Perioperative use of 5HT3R antagonists does not produce potentially dangerous perioperative electrocardiographic changes and does not seem to warrant a drug safety warning from the Food and Drug Administration.

Direct effects of esmolol and landiolol on cardiac function, coronary vasoactivity, and ventricular electrophysiology in guinea-pig hearts

The ultra-short acting, selective β(1)-adrenergic antagonists landiolol and esmolol are widely used perioperatively; however, little is known about their acute direct actions on the heart. The current study utilized the Langendorff perfused heart system to measure changes in cardiac function and hemodynamics in response to each drug. Furthermore, electrophysiological analysis was performed on isolated ventricular myocytes. Direct application of esmolol significantly decreased systolic left ventricular pressure and heart rate at concentrations > 10 µM, while it dose-dependently increased coronary perfusion pressure. Esmolol also shortened the action potential duration (APD) in a concentration-dependent manner, an action maintained even when the delayed rectifier K(+) current or ATP sensitive K(+) current was blocked. Moreover, esmolol inhibited both the inward rectifier K(+) current (I(K1)) and the L-type Ca(2+) current (I(CaL)) and increased the outward current dose-dependently. In contrast, landiolol had minimal cardiac effects. In the Kyoto Model computer simulation, inhibition of either I(K1) or I(CaL) alone failed to shorten the APD; however, an additional increase in the time-independent outward current caused shortening of the APD, equal to that induced by esmolol. In conclusion, esmolol directly inhibits cardiac performance significantly more so than landiolol, an effect revealed to be at least in part mediated by esmolol-induced APD shortening.

Anesthesia induction with sevoflurane and propofol: evaluation of P-wave dispersion, QT and corrected QT intervals

The present study compared the effects of anesthesia induction with sevoflurane and propofol on hemodynamics, P-wave dispersion (Pwd), QT interval and corrected QT (QTc) interval. A total of 72 adult patients were included in this prospective study. All patients had control electrocardiograms (ECGs) before anesthesia induction. Anesthesia was induced with sevoflurane inhalation or intravenous propofol. Electrocardiography for all patients was performed during the 1(st) and 3(rd) minutes of induction, 3 minutes after administration of muscle relaxant, and at 5 minutes and 10 minutes after intubation. Pwd and QT intervals were measured on all ECGs. QTc intervals were determined using the Bazett formula. There was no significant difference in Pwd and QT and QTc intervals on control ECGs. In the sevoflurane group, except for control ECGs, Pwd and QTc interval on all ECGs were significantly longer than those in the propofol group (p < 0.05). We conclude that propofol should be used for anesthesia induction in patients with a predisposition to preoperative arrhythmias, and in those whose Pwd and QTc durations are prolonged on preoperative ECGs.

Drug-induced arrhythmias

The objective of this review is to characterize the mechanisms, risk factors, and offending pharmacotherapeutic agents that may cause drug-induced arrhythmias in critically ill patients. PubMed, other databases, and citation review were used to identify relevant published literature. The authors independently selected studies based on relevance to the topic. Numerous drugs have the potential to cause drug-induced arrhythmias. Drugs commonly administered to critically ill patients are capable of precipitating arrhythmias and include antiarrhythmics, antianginals, antiemetics, gastrointestinal stimulants, antibacterials, narcotics, antipsychotics, inotropes, digoxin, anesthetic agents, bronchodilators, and drugs that cause electrolyte imbalances and bradyarrhythmias. Drug-induced arrhythmias are insidious but prevalent. Critically ill patients frequently experience drug-induced arrhythmias; however, enhanced appreciation for this adverse event has the potential to improve prevention, treatment, patient safety, and outcomes in this patient population.

Evaluation of drug-induced QT prolongation in a halothane-anesthetized monkey model: effects of sotalol

INTRODUCTION

Cynomolgus monkeys are used in in vivo models of safety pharmacological studies to evaluate the effects of drug candidates on the cardiovascular system. Models using halothane-anesthetized animals have been used for the detection of drug-induced QT interval prolongation, but few studies with anesthetized monkeys have been reported.

METHODS

The electrophysiological changes induced by dl-sotalol, a representative class III antiarrhythmic drug, were assessed in halothane-anesthetized monkeys (n = 4) or conscious and unrestrained monkeys (n = 4).

RESULTS

In terms of basal characteristics, the QT interval was longer and the heart rate (HR) was lower under anesthesia than those under conscious conditions. Intravenous administration of 0.1 to 3 mg/kg dl-sotalol to anesthetized monkeys decreased the HR and prolonged the QT interval, monophasic action potential (MAP) duration and ventricular effective refractory period in a dose-dependent manner. In addition, reverse use-dependent prolongation of MAP duration was detected by electrical pacing, whereas the terminal repolarization period was hardly affected at any dose. Oral administration of 3 to 30 mg/kg dl-sotalol to conscious monkeys also decreased the HR and prolonged the QT interval in a dose-dependent manner. When compared at similar plasma concentrations of sotalol, the extent of QT interval prolongation under halothane anesthesia was equal to or greater than that under conscious conditions.

DISCUSSION

The sensitivity for detection of drug-induced QT prolongation under halothane anesthesia may be satisfactory compared with that under conscious conditions. The present examinations indicated the usefulness of a model using halothane-anesthetized monkeys for evaluation of drug-induced QT interval prolongation.

[Long QT syndrome and anaesthesia]

The long QT syndrome (LQTS) is a rare, congenital or acquired disease, which may lead to fatal cardiac arrhythmias (torsade de pointes, TdP). In all LQTS subtypes, TdPs are caused by disturbances in cardiac ion channels. Diagnosis is made using clinical, anamnestic and electrocardiographic data. Triggers of TdPs are numerous and should be avoided perioperatively. Sufficient sedation and preoperative correction of electrolyte imbalances are essential. Volatile anaesthetics and antagonists of muscle relaxants should be avoided and high doses of local anaesthetics are not recommended to date. Propofol is safe for anaesthesia induction and maintenance. The acute therapy of TdPs with cardiovascular depression should be performed in accordance with the guidelines for advanced cardiac life support and includes cardioversion/defibrillation and magnesium. Torsades de pointes may be associated with bradycardia or tachycardia resulting in specific therapeutic and prophylactic measures.

FUNCTIONAL INTERACTION BETWEEN DPI 201-106, A DRUG THAT MIMICS CONGENITAL LONG QT SYNDROME, AND SEVOFLURANE ON THE GUINEA-PIG CARDIAC ACTION POTENTIAL

1. Sevoflurane produces QT prolongation on the electrocardiogram, predominantly via inhibition of the slow delayed rectifier K(+) current. DPI 201-106 is an experimental drug that produces QT prolongation by reducing Na(+) channel inactivation, thereby mimicking congenital long QT syndrome type 3 (LQT3). The present study explores the electrophysiological consequences of administration of sevoflurane in the presence of impaired Na(+) channel activity. 2. We examined the effects of sevoflurane and DPI 201-106, alone and in combination, on the cardiac action potential of guinea-pig ventricular myocytes using standard microelectrode techniques. 3. Both sevoflurane and DPI-201-106 prolonged action potential duration, with the combination of the two drugs producing greater than additive effects. Similarly, instability and triangulation of the action potential waveform, measures of pro-arrhythmia, were more pronounced when both drugs were combined. 4. Sevoflurane treatment significantly alters cardiac action potential waveforms when administered in the presence of impaired Na(+) channel inactivation. These results indicate the potential for ventricular arrhythmia when sevoflurane is administered to LQT3 patients and suggests caution when using sevoflurane in this population.

Electrophysiologic Mechanism Underlying Action Potential Prolongation by Sevoflurane in Rat Ventricular Myocytes

Background:

Despite prolongation of the QTc interval in humans during sevoflurane anesthesia, little is known about the mechanisms that underlie these actions. In rat ventricular myocytes, the effect of sevoflurane on action potential duration and underlying electrophysiologic mechanisms were investigated.

Methods:

The action potential was measured by using a current clamp technique. The transient outward K+ current was recorded during depolarizing steps from −80 mV, followed by brief depolarization to −40 mV and then depolarization up to +60 mV. The voltage dependence of steady state inactivation was determined by using a standard double-pulse protocol. The sustained outward current was obtained by addition of 5 mm 4-aminopyridine. The inward rectifier K+ current was recorded from a holding potential of −40 mV before their membrane potential was changed from −130 to 0 mV. Sevoflurane actions on L-type Ca2+ current were also obtained.

Results:

Sevoflurane prolonged action potential duration, whereas the amplitude and resting membrane potential remained unchanged. The peak transient outward K+ current at +60 mV was reduced by 18 ± 2% (P &lt; 0.05) and 24 ± 2% (P &lt; 0.05) by 0.35 and 0.7 mm sevoflurane, respectively. Sevoflurane had no effect on the sustained outward current. Whereas 0.7 mm sevoflurane did not shift the steady state inactivation curve, it accelerated the current inactivation (P &lt; 0.05). The inward rectifier K+ current at −130 mV was little altered by 0.7 mm sevoflurane. L-type Ca2+ current was reduced by 28 ± 3% (P &lt; 0.05) and 33 ± 1% (P &lt; 0.05) by 0.35 and 0.7 mm sevoflurane, respectively.

Conclusions:

Action potential prolongation by clinically relevant concentrations of sevoflurane is due to the suppression of transient outward K+ current in rat ventricular myocytes.

Effects of sevoflurane on the cAMP-induced short-circuit current in mouse tracheal epithelium and recombinant Cl- (CFTR) and K+ (KCNQ1) channels

BACKGROUND

An optimal level of airway surface liquid is essential for mucociliary clearance in lungs. The cAMP-activated cystic fibrosis transmembrane conductance regulator (CFTR) and KCNQ1 channels in tracheal epithelium play key roles in luminal and basolateral membranes, respectively. The aim of this study was to examine the effects of sevoflurane on cAMP-induced chloride secretion by the mouse tracheal epithelium and the modulation of recombinant CFTR and KCNQ1 channels.

METHODS

The equivalent short-circuit current (Isc) of the mouse tracheal epithelium was measured using a flow-type Ussing chamber technique. Inhibition of Na+ absorption was achieved through the luminal application of amiloride. cAMP-dependent Cl- secretion was evoked by forskolin and isobutylmethylxanthine (Fsk/IBMX) applied to the basolateral side. The effect of sevoflurane on CFTR and KCNQ1 channels was assessed using a whole-cell patch clamp in human embryonic kidney 293T cells expressing CFTR and KCNQ1 channels.

RESULTS

Fsk/IBMX induced a sustained Isc that was suppressed by the application of sevoflurane [decreased by 49 (4.5)% at 190 microM]. The Fsk/IBMX-induced Isc was also blocked by basolateral application of chromanol 293B, a blocker of the KCNQ1 K+ channel. In KCNQ1-expressing cells, sevoflurane 190 microM reduced the outward currents to 59 (4.9)% at 80 mV. The CFTR current was not affected by sevoflurane (approximately 360 microM).

CONCLUSIONS

These results suggest that the inhibition of KCNQ1 underlies sevoflurane-induced decrease in airway secretion.

Reduction of repolarization reserve by halothane anaesthesia sensitizes the guinea-pig heart for drug-induced QT interval prolongation

The utility of halothane-anaesthetized guinea-pigs as an in vivo model for predicting the clinical potential of a drug to induce QT interval prolongation was assessed using the electrocardiogram and monophasic action potential (MAP) recordings with electrical ventricular pacing. Intravenous administration of D-sotalol (0.3 mg kg(-1)) and terfenadine (0.3 mg kg(-1)), blockers of a rapid component of delayed rectifier potassium currents, prolonged the QT interval by 32+/-7 and 23+/-6 ms, respectively, whereas chromanol 293B (1 mg kg(-1)), a blocker of a slow component of delayed rectifier potassium currents, lengthened it by 33+/-8 ms. The extent of the QT interval prolongation by these drugs was greater than those in previous reports using pentobarbital-anaesthetized guinea-pigs. The MAP duration at the control was shortened by decreasing the pacing cycle length from 400 to 200 ms, but the MAP duration at each cycle length was prolonged by D-sotalol. The formulas of Van de Water, Matsunaga, Fridericia and Bazett showed good correlation of the repolarization period when compared with the MAP duration at a pacing cycle length of 400 ms. The halothane-anaesthetized guinea-pig model may possess enough sensitivity to detect drug-induced QT interval prolongation, indicating that halothane anaesthesia can reduce the repolarization reserve of the heart in vivo.

QT-RR relationships and suitable QT correction formulas for halothane-anesthetized dogs

Several QT correction (QTc) formulas have been used for assessing the QT liability of drugs. However, they are known to under- and over-correct the QT interval and tend to be specific to species and experimental conditions. The purpose of this study was to determine a suitable formula for halothane-anesthetized dogs highly sensitive to drug-induced QT interval prolongation. Twenty dogs were anesthetized with 1.5% halothane and the relationship between the QT and RR intervals were obtained by changing the heart rate under atrial pacing conditions. The QT interval was corrected for the RR interval by applying 4 published formulas (Bazett, Fridericia, Van de Water, and Matsunaga); Fridericia's formula (QTcF = QT/RR(0.33)) showed the least slope and lowest R(2) value for the linear regression of QTc intervals against RR intervals, indicating that it dissociated changes in heart rate most effectively. An optimized formula (QTcX = QT/RR(0.3879)) is defined by analysis of covariance and represents a correction algorithm superior to Fridericia's formula. For both Fridericia's and the optimized formula, QT-prolonging drugs (d,l-sotalol, astemizole) showed QTc interval prolongation. A non-QT-prolonging drug (d,l-propranolol) failed to prolong the QTc interval. In addition, drug-induced changes in QTcF and QTcX intervals were highly correlated with those of the QT interval paced at a cycle length of 500 msec. These findings suggest that Fridericia's and the optimized formula, although the optimized is a little bit better, are suitable for correcting the QT interval in halothane-anesthetized dogs and help to evaluate the potential QT prolongation of drugs with high accuracy.

Characterization of the halothane-anesthetized guinea-pig heart as a model to detect the K+ channel blocker-induced QT-interval prolongation

Our previous study using the urethane-anesthetized guinea-pig model has shown that an I(Ks) blocker chromanol 293B hardly affects the QT interval itself nor potentiates the I(Kr) blocker-induced QT-interval prolongation. The former is in good accordance with the previous results in the human isolated intact ventricular tissue, but the latter is in sharp contrast with them. In this study, we characterized the ventricular repolarization ability of a newly developed halothane-anesthetized guinea-pig model by using I(Kr) and I(Ks) blockers. Intravenous administration of a selective I(Kr) blocker d-sotalol (3 mg/kg) prolonged the QT interval by +27 ms. On the other hand, intravenous administration of chromanol 293B (1 mg/kg) prolonged the QT interval by +35 ms, and additional administration of the same dose of d-sotalol further prolonged the QT interval by +48 ms. These results suggest that the abundance of the repolarization reserve among the current and previous models may be in the order of the urethane-anesthetized guinea-pig heart>human intact ventricular tissue>halothane-anesthetized guinea-pig heart. Thus, the halothane-anesthetized guinea-pig model may be considered to be more sensitive than the previous models in predicting the QT-interval prolonging effects of new drugs in patients with high risks for the acquired long QT syndrome.

Halothane sensitizes the guinea-pig heart to pharmacological IKr blockade: comparison with urethane anesthesia

Potential utility of halothane-anesthetized guinea pigs for detecting drug-induced repolarization delay was analyzed in comparison with urethane-anesthesia (n = 4 for both groups). Basal QT interval was significantly greater under halothane-anesthesia than urethane-anesthesia (192 +/- 7 vs 132 +/- 5 ms, respectively), whereas the reverse was true for the heart rate (190 +/- 7 vs 248 +/- 11 beats/min, respectively). The typical I(Kr)-blocker dl-sotalol (0.1 to 3 mg/kg, i.v.) induced dose-related bradycardia and QT interval prolongation under each anesthesia. The extent of maximum prolongation in the QT interval was greater under halothane-anesthesia than urethane-anesthesia (+101 +/- 15 vs +49 +/- 3 ms, respectively), whereas that of peak change in the heart rate was smaller under the former than the latter (-49 +/- 8 vs -63 +/- 5 beats/min, respectively). Pretreatment of the animals under urethane-anesthesia with the selective I(Ks) blocker chromanol 293B (n = 6) increased the extent of the dl-sotalol-induced QT interval prolongation to +57 +/- 8 ms, which was only 0.56 times of that under the halothane-anesthesia, whereas the pretreatment increased the peak change in the heart rate to -76 +/- 12 ms. These results indicate that the halothane-anesthesia may effectively sensitize the guinea-pig heart to pharmacological I(Kr) blockade.

Halothane sensitizes the canine heart to pharmacological IKr blockade

The effects of halothane and pentobarbital on the cardiovascular system were compared using the in vivo canine models. The ventricular repolarization process was longer under the halothane-anesthesia than pentobarbital-anesthesia. Intravenous administration of a selective blocker of rapidly activating delayed rectifier K+ currents (I(Kr)) sematilide prolonged the ventricular repolarization period without affecting the intraventricular conduction under both anesthesia; however, the potency was about 1.5-folds greater under the halothane-anesthesia than pentobarbital-anesthesia. These results suggest that halothane can more effectively sensitize the heart to pharmacological I(Kr) blockade, resulting in the excessive QT interval prolongation. Thus, the halothane-anesthetized canine model can be useful for predicting the in vivo I(Kr) blocking property of new drugs.