Differences in cardiotoxicity of bupivacaine and ropivacaine are the result of physicochemical and stereoselective properties

BACKGROUND: Ropivacaine is believed to have a lower incidence of clinical cardiac side effects than bupivacaine. The aim of this study was to compare the direct cardiac effects of the optically pure S(-)-ropivacaine isomer and its nonclinically used R(+)-isomer with both optically pure bupivacaine isomers in isolated hearts. The hypothesis was that differences in direct cardiac effects are distinguished not only by stereoselective actions of local anesthetic molecules to specific receptors, but also by physicochemical differences triggered by replacing the butyl- by a propyl-residual on pipecoloxylide. METHODS: Guinea pig hearts (n = 31) were excised and perfused by the Langendorff method. Atrial and ventricular bipolar electrodes were placed to measure heart rate and atrioventricular conduction time. Left ventricular pressure, coronary flow, and oxygen tensions were measured. Twelve hearts were perfused with increasing concentrations (0.5, 1.0, 5.0, and 10 microm) of both isomers of bupivacaine, and 13 hearts were perfused with the same concentrations of ropivacaine isomers. Six hearts were perfused with higher concentrations (20, 30, 40, and 50 microm) of both isomers of ropivacaine. The order of isomers and anesthetic chosen were randomized. RESULTS: Both anesthetics had negative inotropic and chronotropic effects without evidence of stereoselectivity. Equal concentrations of both isomers of bupivacaine had negative inotropic effects greater than that of ropivacaine isomers. Atrioventricular conduction time was prolonged by both anesthetics in a concentration-dependent manner, but bupivacaine isomers increased atrioventricular conduction time more than ropivacaine isomers. In contrast to other variables, atrioventricular conduction time showed evident stereoselectivity for bupivacaine at the lowest concentration (0.5 microm) but only at higher concentrations for ropivacaine (> 30 microm). The R(+)-isomer was more potent than the S(-)-isomer on increasing atrioventricular conduction time for both bupivacaine and ropivacaine. CONCLUSIONS: The results confirm that stereoselectivity can be demonstrated by a lengthening of atrioventricular conduction time for the more fat-soluble bupivacaine. However, for the less fat-soluble ropivacaine, the S(-)-isomer has no advantage over the R(+)-isomer for preventing slowing of atrioventricular conduction in clinical concentrations. Neither anesthetic showed stereoselective inotropic effects, but ropicavaine isomers had lesser cardiodepressant effects than bupivacaine isomers because of the replacement of the butyl- by a propyl-terminal group.     

Molecular Mechanisms of the Inhibitory Effects of Bupivacaine, Levobupivacaine, and Ropivacaine on Sarcolemmal Adenosine Triphosphate-sensitive Potassium Channels in the Cardiovascular System

Background: Sarcolemmal adenosine triphosphate-sensitive potassium (KATP) channels in the cardiovascular system may be involved in bupivacaine-induced cardiovascular toxicity. The authors investigated the effects of local anesthetics on the activity of reconstituted KATP channels encoded by inwardly rectifying potassium channel (Kir6.0) and sulfonylurea receptor (SUR) subunits.

Methods: The authors used an inside-out patch clamp configuration to investigate the effects of bupivacaine, levobupivacaine, and ropivacaine on the activity of reconstituted KATP channels expressed in COS-7 cells and containing wild-type, mutant, or chimeric SURs.

Results: Bupivacaine inhibited the activities of cardiac KATP channels (IC50 = 52 [mu]m) stereoselectively (levobupivacaine, IC50 = 168 [mu]m; ropivacaine, IC50 = 249 [mu]m). Local anesthetics also inhibited the activities of channels formed by the truncated isoform of Kir6.2 (Kir6.2[DELTA]C36) stereoselectively. Mutations in the cytosolic end of the second transmembrane domain of Kir6.2 markedly decreased both the local anesthetics' affinity and stereoselectivity. The local anesthetics blocked cardiac KATP channels with approximately eightfold higher potency than vascular KATP channels; the potency depended on the SUR subtype. The 42 amino acid residues at the C-terminal tail of SUR2A, but not SUR1 or SUR2B, enhanced the inhibitory effect of bupivacaine on the Kir6.0 subunit.     

Effects of Bupivacaine and Ropivacaine on High-voltage-activated Calcium Currents of the Dorsal Horn Neurons in Newborn Rats

Background: Local anesthetics, such as bupivacaine, have been reported to block calcium currents in primary sensory neurons and to interfere with the release of neurotransmitters in central nervous system neurons. However, it is unknown whether local anesthetics affect the calcium current activity of central nervous system neurons.

Methods: Using a traditional whole cell voltage clamp technique, effects of bupivacaine and ropivacaine on high-voltage-activated calcium currents (HVA-Ica) were investigated in enzymatically dissociated dorsal horn neurons of neonatal rats. Calcium currents were evoked by testing pulses from a holding potential of -90 to 0 mV.

Results: Bupivacaine significantly reduced HVA-Ica in a dose-dependent manner. The peak HVA-Ica decreased by 24.5 +/- 2.5, 32.0 +/- 6.8, 59.4 +/- 6.2, 88.3 +/- 1.5, and 91.6 +/- 1.1% in response to 10, 30, 50, 100 and 200 [mu]m bupivacaine, respectively. Unlike bupivacaine, ropivacaine markedly increased HVA-Ica at lower concentrations (< 50 [mu]m) but decreased HVA-Ica at higher concentrations (>= 50 [mu]m). The percent increases in peak HVA-Ica induced by 10 and 30 [mu]m ropivacaine were 95 +/- 19.1 and 41.6 +/- 8.3%, respectively. The percent decreases in response to 50, 100, and 200 [mu]m ropivacaine were 21.1 +/- 2.1, 63.2 +/- 6.0 and 79.1 +/- 7.6%, respectively. Results indicate that the inhibitory potency of ropivacaine on HVA-Ica was significantly lower than that of bupivacaine at the same concentrations.     

Local Anesthetic Interaction with Human Ether-a-go-go-related Gene (HERG) Channels: Role of Aromatic Amino Acids Y652 and F656

Background: Human ether-a-go-go-related gene (HERG) potassium channels constitute a potential target involved in cardiotoxic side effects of amino-amide local anesthetics. The molecular interaction site of these low-affinity blockers with HERG channels is currently unknown. The aim of this study was to determine the effect of the mutations Y652A and F656A in the putative drug binding region of HERG on the inhibition by bupivacaine, ropivacaine, and mepivacaine.

Methods: The authors examined the inhibition of wild-type and mutant HERG channels, transiently expressed in Chinese hamster ovary cells by bupivacaine, ropivacaine, and mepivacaine. Whole cell patch clamp recordings were performed at room temperature.

Results: Inhibition of HERG wild-type and mutant channels by the different local anesthetics was concentration dependent, stereoselective, and reversible. The sensitivity decreased in the order bupivacaine > ropivacaine > mepivacaine for wild-type and mutant channels. The mutant channels were approximately 4-30 times less sensitive to the inhibitory action of the different local anesthetics than the wild-type channel. The concentration-response data were described by Hill functions (bupivacaine: wild-type IC50 = 22 +/- 2 [mu]m, n = 38; Y652A IC50 = 95 +/- 5 [mu]m, n = 31). The mutations resulted in a change of the stereoselectivity of HERG channel block by ropivacaine. The potency of the local anesthetics to inhibit wild-type and mutant channels correlated with the lipophilicity of the drug (r > 0.9).     

Stereospecific Effect of Bupivacaine Isomers on Atrioventricular Conduction in the Isolated Perfused Guinea Pig Heart

Background: The local anesthetic bupivacaine is an equal mixture of two optically active isomers known to exert different cardiotoxic profiles in vivo. Enantiomer-specific forms of bupivacaine may have differential effects on cardiovascular function, specifically on cardiac electrophysiology. The authors' aim was to determine if there were any direct functional differences in the cardiac effects of bupivacaine isomers. The isolated heart was used to avoid possible indirect cardiac effects of bupivacaine, such as autonomic nervous and hormonal influences, as well as preload and afterload factors.

Methods: The hearts of 12 ketamine-anesthetized guinea pigs were perfused with Krebs-Ringer's solution (97% oxygen, 3% carbon dioxide) at constant perfusion pressure using the Langendorff technique. Atrial and ventricular bipolar electrodes were placed to measure heart rate (HR) and atrioventricular (AV) conduction time. Left ventricular pressure (LVP), coronary flow, and inflow and outflow oxygen tensions were also measured. Oxygen delivery, oxygen consumption (MVO2), and percentage of oxygen extraction were calculated. Each heart was perfused with increasing randomized concentrations (0.5, 1, 5, 10 micro Meter) of both isomers and the racemate of bupivacaine.

Results: Racemic and isomeric bupivacaine equally and dose dependently decreased cardiac function. At 10 micro Meter bupivacaine these changes were HR, -17 +/- 2%; LVP, -50 +/- 3%; coronary flow, -20 +/- 40%; and MVO2, -46 +/- 40%. The (+) isomer significantly prolonged AV conduction compared with the racemate and the (-) isomer at all concentrations. At 10 micro Meter, AV time was 54 +/- 6% longer with the (+) isomer and 30 +/- 4% longer with the (+/-) racemate than with the (-) isomer. The greater delay in AV time with the (+) than the racemate or (-) isomer led to a second-degree AV dissociation in 10 of 12 of hearts treated with (+) bupivacaine.     

Comparison of the Effects of Racemic Bupivacaine, Levobupivacaine, and Ropivacaine on Ventricular Conduction, Refractoriness, and Wavelength: An Epicardial Mapping Study

Background: The study was designed to compare the effects of equimolar concentrations of racemic bupivacaine, levobupivacaine, and ropivacaine on ventricular conduction, anisotropy, duration and homogeneity of refractoriness, and wavelengths, and to provide a potency ratio for effects on conduction velocity.

Methods: Isolated frozen rabbit hearts (which leave a thin layer of surviving epicardial muscle) were treated with 0.1, 1, and 10 [mu]m racemic bupivacaine, levobupivacaine, or ropivacaine. Left ventricular longitudinal and transverse conduction velocities, anisotropic ratio, minimum pacing cycle length, use dependency, duration and dispersion of ventricular effective refractory period, and wavelengths were studied. A high-resolution mapping system was used for data acquisition. In addition to two-way analysis of variance for repeated measures, data for conduction velocities were fitted simultaneously using a nonlinear mixed-effect modeling program to allow intergroup comparison.

Results: Each agent induced a concentration- and use-dependent slowing of conduction velocities, with no change of the anisotropic ratio. The use-dependent effect of levobupivacaine is similar to that of racemic bupivacaine concerning longitudinal conduction velocity. Fitting of conduction velocities provided a racemic bupivacaine to levobupivacaine and to ropivacaine ratio of 1:1.38 for concentration effect at 1,000-ms pacing cycle length, and 1:0.74 for use-dependent effect at 600-ms pacing cycle length. Racemic bupivacaine and levobupivacaine prolonged the ventricular effective refractory period, whereas ropivacaine did not. No dispersion in ventricular effective refractory period values occurred. All three agents induced significant decreases in wavelengths. This effect was not different among groups.     

Local Anesthetics Impair Human Granulocyte Phagocytosis Activity, Oxidative Burst, and CD11b Expression in Response to Staphylococcus aureus

Background: With invasion of bacteria, the host defense system is activated by a complex cascade of various mechanisms. Local anesthetics previously were shown to interact with diverse components of the immune response, such as leukocyte adherence on endothelial monolayers, oxidative burst, or crosstalk within lymphocyte subset populations. However, effects of newer local anesthetics like bupivacaine and ropivacaine on antibacterial host defense-primarily phagocytosis activity, oxidative burst, or CD11b expression-still remain unclear.

Methods: Whole blood samples were preincubated with local anesthetics (lidocaine, 9.2, 92.2, and 1,846 [mu]m; bupivacaine, 6.1, 61, and 770 [mu]m; ropivacaine, 6.4, 64, and 801 [mu]m). For the oxidative burst and CD11b assay, dihydroethidium was added to the probes. After viable Staphylococcus aureus was added in a 5 to 1 ratio following leukocyte count, phagocytosis was stopped at different times, and staining with monoclonal antibodies was performed for subsequent flow cytometric analysis of phagocytosis activity, oxidative burst, and CD11b expression.

Results: Granulocyte phagocytosis activity, CD11b expression, and generation of reactive oxygen species were significantly reduced by lidocaine (P < 0.0002) and bupivacaine (P < 0.005) in the highest concentration (1,846 [mu]m and 770 [mu]m, respectively). The capability of granulocytes to ingest bacteria was significantly depressed only by lidocaine (P < 0.003). Ropivacaine had no significant effect on any parameter investigated.     

Comparative Effects of Bupivacaine and Ropivacaine on Intracellular Calcium Transients and Tension in Ferret Ventricular Muscle

Background: Recent evidence suggests that ropivacaine exerts markedly less cardiotoxicity compared with bupivacaine; however, the mechanisms are not fully understood at the molecular level.

Methods: Isolated ferret ventricular papillary muscles were microinjected with the Ca2+-binding photoprotein aequorin, and intracellular Ca2+ transients and tension were simultaneously measured during twitch in the absence and presence of bupivacaine or ropivacaine.

Results: Bupivacaine and ropivacaine (10, 30, and 100 [mu]m) reduced peak systolic [Ca2+]i and tension in a concentration-dependent manner. The effects were significantly greater for bupivacaine, particularly on tension (approximately twofold). The percentage reduction of tension was linearly correlated with that of [Ca2+]i for both anesthetics, with the slope of the relationship being [almost equal to]1.0 for ropivacaine and [almost equal to]1.3 for bupivacaine (slope difference, P < 0.05), suggesting that the cardiodepressant effect of ropivacaine results predominantly from inhibition of Ca2+ transients, whereas bupivacaine suppresses Ca2+ transients and the reaction beyond Ca2+ transients, i.e., myofibrillar activation, as well. BAY K 8644, a Ca2+ channel opener, abolished the inhibitory effects of ropivacaine on Ca2+ transients and tension, whereas BAY K 8644 only partially inhibited the effects of bupivacaine, particularly the effects on tension.     

Comparative Ventricular Electrophysiologic Effect of Racemic Bupivacaine, Levobupivacaine, and Ropivacaine on the Isolated Rabbit Heart

Background: Numerous local anesthetics have an asymmetric tetrahedron carbon, which confers stereoselective differences between the isomers. The authors attempted to quantify the depressant effect of racemic bupivacaine, levobupivacaine, and ropivacaine on myocardial ventricular conduction and on myocardial contractility.

Methods: The authors studied the pharmacokinetics (outflow concentration) and pharmacodynamics (QRS widening) of the three drugs infused in an isolated rabbit heart preparation. All data were fitted simultaneously with use of mixed-effect modeling, thus allowing precise statistical comparison between the three drug parameters. The rate dependence of QRS widening was fitted separately.

Results: Racemic bupivacaine, levobupivacaine, and ropivacaine induced a calculated maximum increase in QRS duration in the ratio 1:0.4:0.3. Css50, the dose which caused half the maximum increase in QRS duration at steady state, was similar for all three drugs (22 [mu]m free concentration). A rate dependence of QRS widening was observed, which was in the ratio 1:0.5:0.25 for racemic bupivacaine, levobupivacaine, and ropivacaine, respectively.     

Effects of bupivacaine, levobupivacaine and ropivacaine on myocardial relaxation

PURPOSE: Ropivacaine and levobupivacaine were developed to reduce the risk of occasional toxicity reported with bupivacaine. While the effects of long-acting local anesthetics (LAAs) on myocardial contractility (inotropy) are well described, their effects on relaxation (lusitropy) remain largely unknown. The present study aimed to compare the effects of LAAs on rat myocardium. METHODS: Left ventricular papillary muscles of male Wistar rats were used to compare the inotropic and lusitropic responses of increasing concentrations of LAAs (10(-8) to 10(-3) M) under isometric and isotonic conditions. Data are mean % (SD) of baseline value. RESULTS: Long-acting local anesthetics induced a significant impairment of relaxation in isotonic and isometric conditions. As compared to ropivacaine, bupivacaine and levobupivacaine induced greater negative lusitropic effects in isotony [at 10(-3) M, maximum unloaded shortening velocity ((max)Vr) = 27 +/- 11 vs 13 +/- 6 and 8 +/- 5%] and isometry (at 10(-3) M, time-to-half-relaxation: 106 +/- 10 vs 127 +/- 17 and 133 +/- 17%). When the comparison was made with equipotent concentrations, the negative lusitropic effects induced with levobupivacaine were significantly greater than those of bupivacaine and ropivacaine in isometric and isotonic conditions (at 10(-3) M, (max)Vr = 7 +/- 4 vs 13 +/- 6 and 17 +/- 4 %). As previously described, LAAs also induced concentration-dependent negative inotropic effects that were greater for levobupivacaine compared to equivalent or equipotent concentrations of bupivacaine and ropivacaine. CONCLUSIONS: Long-acting local anesthetics induce marked negative inotropic and lusitropic effects. Among LAAs, levobupivacaine exerts the greater depressant effects. Impairment of calcium handling and sarcoplasmic reticulum could explain the differential responses to local anesthetics.     

Effect of Bupivacaine and Levobupivacaine on Exocytotic Norepinephrine Release from Rat Atria

Background: The cardiotoxic mechanism of local anesthetics may include interruption of cardiac sympathetic reflexes. The authors undertook this investigation to determine if clinically relevant concentrations of bupivacaine and levobupivacaine interfere with exocytotic norepinephrine release from cardiac sympathetic nerve endings.

Methods: Rat atria were prepared for measurements of twitch contractile force and 3[H]-norepinephrine release. After nerve endings were loaded with 3[H]-norepinephrine, the tissue was electrically stimulated in 5-min episodes during 10 10-min sampling periods. After each period, a sample of bath fluid was analyzed for radioactivity and 3[H]-norepinephrine release was expressed as a fraction of tissue counts. Atria were exposed to buffer alone during sampling periods 1 and 2 (S1 and S2). Control atria received saline (100 [mu]l each, n = 6 atria) in S3-S10. Experimental groups (n = 6 per group) received either bupivacaine or levobupivacaine at concentrations (in [mu]M) of 5 (S3-S4), 10 (S5-S6), 30 (S7-S8), and 100 (S9-S10).

Results: Bupivacaine and levobupivacaine decreased stimulation-evoked fractional 3[H]-norepinephrine release with inhibitory concentration 50% values of 5.1 +/- 0.5 and 6.1 +/- 1.3 [mu]m. The inhibitory effect of both local anesthetics (~70%) approached that of tetrodotoxin. Local anesthetics abolished the twitch contractions of atria with inhibitory concentration 50% values of 12.6 +/- 5.0 [mu]m (bupivacaine) and 15.7 +/- 3.9 [mu]m (levobupivacaine). In separate experiments, tetrodotoxin inhibited twitch contractile force by only 30%.     

Effects of Ropivacaine on Action Potential Configuration and Ion Currents in Isolated Canine Ventricular Cardiomyocytes

Background: Despite the widespread clinical application of ropivacaine, there is little information on the cellular cardiac effects of the drug. In the current study, therefore, the concentration-dependent effects of ropivacaine on action potential morphology and the underlying ion currents were studied and compared with those of bupivacaine in isolated canine ventricular cardiomyocytes.

Methods: Action potentials were recorded from the enzymatically dispersed cells using sharp microelectrodes. Conventional patch clamp and action potential voltage clamp arrangements were used to study the effects of ropivacaine on transmembrane ion currents.

Results: Ropivacaine induced concentration- and frequency-dependent changes in action potential configuration, including shortening of the action potentials, reduction of their amplitude and maximum velocity of depolarization, suppression of early repolarization, and depression of plateau. Reduction in maximum velocity of depolarization was characterized with an EC50 value of 81 +/- 7 [mu]m at 1 Hz. Qualitatively similar results were obtained with bupivacaine (EC50 = 47 +/- 3 [mu]m). Under voltage clamp conditions, a variety of ion currents were blocked by ropivacaine: L-type calcium current (EC50 = 263 +/- 67 [mu]m), transient outward current (EC50 = 384 +/- 75 [mu]m), inward rectifier potassium current (EC50 = 372 +/- 35 [mu]m), rapid delayed rectifier potassium current (EC50 = 303 +/- 47 [mu]m), and slow delayed rectifier potassium current (EC50 = 106 +/- 18 [mu]m).     

Differential effects of bupivacaine and ropivacaine enantiomers on intracellular Ca2+ regulation in murine skeletal muscle fibers

BACKGROUND: Increased intracellular Ca concentrations are considered to be a major pathomechanism in local anesthetic myotoxicity. Racemic bupivacaine and S-ropivacaine cause Ca release from the sarcoplasmic reticulum of skeletal muscle fibers and simultaneously inhibit Ca reuptake. Examining the optical isomers of both agents, the authors investigated stereoselective effects on muscular Ca regulation to get a closer insight in subcellular mechanisms of local anesthetic myotoxicity. METHODS: R- and S-enantiomers as well as racemic mixtures of both agents were tested in concentrations of 1, 5, 10, and 15 mm. Saponin-skinned muscle fibers from the extensor digitorum longus muscle of BALB/c mice were examined according to a standardized procedure. For the assessment of effects on Ca uptake and release from the sarcoplasmic reticulum, agents were added to the loading solution and the release solution, respectively, and force and Ca transients were monitored. RESULTS: The effects of S-enantiomers on both Ca release and reuptake were significantly more pronounced than those of racemic mixtures and R-enantiomers, respectively. In addition, the effects of racemates were markedly stronger than those of R-enantiomers. With regard to Ca release, the effects of bupivacaine isomers were more pronounced than the isomers of ropivacaine. CONCLUSIONS: These data show that stereoselectivity is involved in alterations of intracellular Ca regulation by bupivacaine and ropivacaine. S-enantiomers seem to be more potent than R-enantiomers, with intermediate effects of racemic mixtures. In addition, lipophilicity also seems to determine the extent of Ca release by local anesthetics.     

Comparison of the effects of racemic bupivacaine, levobupivacaine, and ropivacaine on ventricular conduction, refractoriness, and wavelength: an epicardial mapping study

BACKGROUND: The study was designed to compare the effects of equimolar concentrations of racemic bupivacaine, levobupivacaine, and ropivacaine on ventricular conduction, anisotropy, duration and homogeneity of refractoriness, and wavelengths, and to provide a potency ratio for effects on conduction velocity. METHODS: Isolated frozen rabbit hearts (which leave a thin layer of surviving epicardial muscle) were treated with 0.1, 1, and 10 mum racemic bupivacaine, levobupivacaine, or ropivacaine. Left ventricular longitudinal and transverse conduction velocities, anisotropic ratio, minimum pacing cycle length, use dependency, duration and dispersion of ventricular effective refractory period, and wavelengths were studied. A high-resolution mapping system was used for data acquisition. In addition to two-way analysis of variance for repeated measures, data for conduction velocities were fitted simultaneously using a nonlinear mixed-effect modeling program to allow intergroup comparison. RESULTS: Each agent induced a concentration- and use-dependent slowing of conduction velocities, with no change of the anisotropic ratio. The use-dependent effect of levobupivacaine is similar to that of racemic bupivacaine concerning longitudinal conduction velocity. Fitting of conduction velocities provided a racemic bupivacaine to levobupivacaine and to ropivacaine ratio of 1:1.38 for concentration effect at 1,000-ms pacing cycle length, and 1:0.74 for use-dependent effect at 600-ms pacing cycle length. Racemic bupivacaine and levobupivacaine prolonged the ventricular effective refractory period, whereas ropivacaine did not. No dispersion in ventricular effective refractory period values occurred. All three agents induced significant decreases in wavelengths. This effect was not different among groups. CONCLUSIONS: Differences among racemic bupivacaine, levobupivacaine, and ropivacaine at equimolar concentrations are mainly caused by the use-dependent effects on conduction velocities and the concentration-dependent effects on ventricular effective refractory period. Therefore, one must take into account the corresponding pacing rates when comparing the potency ratios of local anesthetics.     

Ketamine Has Stereospecific Effects in the Isolated Perfused Guinea Pig Heart

Background: S(+)-Ketamine is judged to produce more potent anesthesia than either the racemate or the R(-) ketamine isomer because of differential activation of specific cerebral receptors. Other than central nervous system effects, the most important side effects of ketamine occur in the cardiovascular system. We examined the direct cardiac effects of the isomers and the racemate of ketamine in the isolated perfused guinea pig heart.

Methods: Twenty-three guinea pig hearts were perfused by the Langendorff technique with modified 37 degrees Celsius Krebs-Ringer's solution (97% oxygen and 3% carbon dioxide) at a constant perfusion pressure. Eight animals were pretreated with reserpine to deplete hearts of catecholamines. These pretreated hearts were also perfused with Krebs-Ringer's solution containing propranolol, phenoxybenzamine, and atropine to block any remaining effects of catecholamines and of acetylcholine. Five additional hearts were perfused with naloxone to block cardiac opioid receptors. Ten hearts were not treated. All 23 hearts were then exposed to four increasing equimolar concentrations of each isomer and the racemate of ketamine for 10 min. Heart rate, atrioventricular conduction time (AVCT), left ventricular pressure, coronary flow, and inflow and outflow oxygen tensions were measured. Percentage oxygen extraction, oxygen delivery, and oxygen consumption were calculated.

Results: Both isomers and the racemate caused a concentration-dependent depression of systolic left ventricular pressure and an increase in AVCT. in the untreated hearts, S(+)-ketamine decreased heart rate and left ventricular pressure and, at higher concentrations, oxygen consumption and percentage oxygen extraction significantly less than R(-)-ketamine independent of blocked or unblocked opioid receptors. Racemic ketamine depressed cardiac function to a degree intermediate to that produced by the isomers. Coronary flow and AVCT were equally affected by the isomers and by the racemic mixture. In the catecholamine-depleted hearts both isomers and the racemate caused equipotent depression of all variables. In these hearts cardiac depression was greater, and AVCT, coronary flow, and oxygen delivery were significantly greater than in untreated and opioid receptor-blocked hearts.     

The inhibitory effects of bupivacaine,levobupivacaine, and ropivacaine on K2P (two-pore domain potassium) channel TREK-1

Purpose

Bupivacaine, levobupivacaine, and ropivacaine are amide local anesthetics. Levobupivacaine and ropivacaine are stereoisomers of bupivacaine and were developed to circumvent the bupivacaine’s severe toxicity. The recently characterized background potassium channel, K_2P TREK-1, is a well-known target for various local anesthetics. The purpose of study is to investigate the differences in inhibitory potency and stereoselectivity among bupivacaine, levobupivacaine, and ropivacaine on K_2P TREK-1 channels overexpressed in COS-7 cells.

Methods

We investigated the effects of bupivacaine, levobupivacaine, and ropivacaine (10, 50, 100, 200, and 400 μM) on TREK-1 channels expressed in COS-7 cells by using the whole cell patch clamp technique with a voltage ramp protocol ranging from ?100 to 100 mV for 200 ms from a holding potential of ?70 mV.

Results

Bupivacaine, levobupivacaine, and ropivacaine showed reversible inhibition of TREK-1 channels in a concentration-dependent manner. The half-maximal inhibitory concentrations (IC₅₀) of bupivacaine, levobupivacaine, and ropivacaine were 95.4 ± 14.6, 126.1 ± 24.5, and 402.7 ± 31.8 μM, respectively. IC₅₀ values indicated a rank order of potency (bupivacaine > levobupivacaine > ropivacaine) with stereoselectivity. Hill coefficients were 0.84, 0.93, and 0.89 for bupivacaine, levobupivacaine, and ropivacaine, respectively.

Conclusion

Inhibitory effects on TREK-1 channels by bupivacaine, levobupivacaine, and ropivacaine demonstrated stereoselectivity: bupivacaine was more potent than levobupivacaine and ropivacaine. Inhibition of TREK-1 channels and consecutive depolarization of the cell membrane by bupivacaine, levobupivacaine, and ropivacaine may contribute to the blockade of neuronal conduction and side effects.     

Enantioselective actions of bupivacaine and ropivacaine on coronary vascular resistance at cardiotoxic concentrations

The main concern with the use of the long-acting local anesthetics bupivacaine and ropivacaine is inadvertent IV injection, which exposes the heart to toxic drug concentrations. We tested the hypothesis that these chiral anesthetics exert enantioselective actions on coronary vascular tone, the regulation of which does not involve voltage-gated Na(+) channels. Coronary perfusion pressure (CPP) was continuously measured in isolated hearts perfused via the aorta at a constant flow rate. This method provides a sensitive assay of coronary vascular resistance in the intact heart. In parallel experiments, we examined the effects of bupivacaine and ropivacaine on intracellular [Ca(2+)] in coronary endothelial cells. In addition, the effect of bupivacaine on mitochondrial membrane potential was assessed using isolated ventricular myocytes. Racemic bupivacaine and R(+)-bupivacaine produced similar dose-dependent decreases in CPP. However, S(-)-bupivacaine, S(-)-ropivacaine and R(+)-ropivacaine increased CPP. In contrast to adenosine triphosphate, neither racemic bupivacaine nor S(-)-ropivacaine changed endothelial intracellular [Ca(2+)], suggesting that these clinically used drugs do not modulate endothelial nitric oxide synthase. We also showed that the putative uncoupler bupivacaine did not depolarize mitochondria in intact ventricular myocytes. In conclusion, the long-acting local anesthetics have enantioselective actions on coronary resistance vessels. Racemic bupivacaine and R(+)-bupivacaine are coronary vasodilators, whereas S(-)-bupivacaine, S(-)-ropivacaine and, to a lesser extent, R(+)-ropivacaine all induce coronary vasoconstriction.     

Cardiac electrophysiologic properties of bupivacaine and lidocaine compared with those of ropivacaine, a new amide local anesthetic

Ropivacaine is a new amino-amide local anesthetic whose anesthetic profile appears similar to that of bupivacaine. Moreover, in intact animals ropivacaine was reportedly less arrhythmogenic than bupivacaine. These experiments evaluated the cardiac transmembrane electrophysiologic effects of ropivacaine compared with those of lidocaine and bupivacaine in an isolated rabbit Purkinje fiberventricular muscle preparation. Only bupivacaine (3-5 micrograms/ml, 0.92-1.5 x 10(-5) m) significantly decreased Purkinje fiber maximum diastolic potential. Action potential amplitude and maximal rate of depolarization (Vmax) were significantly decreased by all agents in the following order: bupivacaine, ropivacaine, lidocaine. High concentrations of bupivacaine and ropivacaine caused premature depolarizations during phase 3 in some preparations. In addition, bupivacaine altered the action potential configuration by producing "notching" not seen with either ropivacaine or lidocaine. This may reflect effects caused by changes in Ca2+, K+, or electrotonic effects. Ropivacaine and bupivacaine (30 micrograms/ml, 9.2 x 10(-5) m) and lidocaine (100 micrograms/ml, 3.74 x 10(-4) m) caused Purkinje fiber inexcitability and Purkinje fiber-ventricular muscle conduction block. However, the duration of PF inexcitability following exposure to ropivacaine and lidocaine was significantly shorter than in bupivacaine-treated preparation. Duration of PF-VM conduction block also tended to be shorter for ropivacaine than bupivacaine, but significantly longer than lidocaine. In general, ropivacaine is less potent than bupivacaine but more potent than lidocaine in terms of its depressant effect on cardiac excitation and conduction.     

Comparative effects of bupivacaine and ropivacaine on intracellular calcium transients and tension in ferret ventricular muscle

BACKGROUND: Recent evidence suggests that ropivacaine exerts markedly less cardiotoxicity compared with bupivacaine; however, the mechanisms are not fully understood at the molecular level. METHODS: Isolated ferret ventricular papillary muscles were microinjected with the Ca-binding photoprotein aequorin, and intracellular Ca transients and tension were simultaneously measured during twitch in the absence and presence of bupivacaine or ropivacaine. RESULTS: Bupivacaine and ropivacaine (10, 30, and 100 microm) reduced peak systolic [Ca]i and tension in a concentration-dependent manner. The effects were significantly greater for bupivacaine, particularly on tension (approximately twofold). The percentage reduction of tension was linearly correlated with that of [Ca]i for both anesthetics, with the slope of the relationship being approximately equal to 1.0 for ropivacaine and approximately equal to 1.3 for bupivacaine (slope difference, P < 0.05), suggesting that the cardiodepressant effect of ropivacaine results predominantly from inhibition of Ca transients, whereas bupivacaine suppresses Ca transients and the reaction beyond Ca transients, i.e., myofibrillar activation, as well. BAY K 8644, a Ca channel opener, abolished the inhibitory effects of ropivacaine on Ca transients and tension, whereas BAY K 8644 only partially inhibited the effects of bupivacaine, particularly the effects on tension. CONCLUSION: The cardiodepressant effect of bupivacaine is approximately twofold greater than that of ropivacaine. Bupivacaine suppresses Ca transients more markedly than does ropivacaine and reduces myofibrillar activation, which may at least in part underlie the greater inhibitory effect of bupivacaine on cardiac contractions. These results suggest that ropivacaine has a more favorable profile as a local anesthetic in the clinical settings.     

Electrophysiologic effects of enflurane and halothane on isolated rabbit hearts in the presence and absence of metabolic acidosis

Electrophysiologic effects of halothane and enflurane in the presence of a normal pH and during metabolic acidosis were examined in isolated rabbit hearts perfused at a constant rate. During exposure to a normal pH, both halothane and enflurane produced concentration-dependent suppression of sinus node automaticity and atrioventricular conduction. Intraatrial and intraventricular conduction times during constant pacing were slightly but significantly prolonged by these anesthetics at 2 MAC. The magnitudes of these electrophysiologic changes were similar with halothane and enflurane when compared at the same MAC. These electrophysiologic effects became more marked during metabolic acidosis (pH 6.9). These results suggest that enflurane and halothane have direct depressant actions on the cardiac conduction system and that these electrophysiologic effects may be augmented by metabolic acidosis.