Block of Neuronal Tetrodotoxin-Resistant Na+ Currents by Stereoisomers of Piperidine Local Anesthetics (original) (raw)
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Local Anesthetic Neurotoxicity Does Not Result from Blockade of Voltage-Gated Sodium Channels
Anesthesia & Analgesia, 1995
To investigate whether local anesthetic neurotoxicity results from sodium channel blockade, we compared the effects of intrathecally administered lidocaine, bupivacaine, and tetrodotoxin (TTX), the latter a highly selective sodium channel blocker, on sensory function and spinal cord morphology in a rat model. First, to determine relative anesthetic potency, 25 rats implanted with intrathecal catheters were subjected to infusions of lidocaine (n = 8), bupivacaine (n = 81, or TTX (n = 9). The three drugs produced parallel dose-effect curves that differed significantly from one another: the EC,, values for lidocaine, bupivacaine, and TTX were 28.2 mM (0.66%), 6.6 mM (0.19%), and 462 nM, respectively. Twenty-five additional rats were then given intrathecal lidocaine (n = 8), bupivacaine (n = 8), or TTX (n = 9) at concentrations 10 times the calculated EC,, for sensory block. Lidocaine and bupivacaine induced persistent sensory impairment, whereas TTX did not. Finally, 28 rats were given either intrathecal bupivacaine (n = 10) or TTX (n = 9) at 10 times the EC,,, or normal saline (n = 9). Significant sensory impairment again occurred after infusion of bupivacaine, but not after infusion of TTX or saline. Neuropathologic evaluation revealed moderate to severe nerve root injury in bupivacaine-treated animals; histologic changes in TTX-and saline-treated animals were minimal, similar, and restricted to the area adjacent to the catheter. These results indicate that local anesthetic neurotoxicity does not result from blockade of the sodium channel, and suggest that development of a safer anesthetic is a realistic goal.
Evidence of presynaptic and postsynaptic action of local anesthetics in rats
Acta Cirurgica Brasileira, 2013
To assess the probable actions of ropivacaine, 50% enantiomeric excess bupivacaine mixture (S75-R25) and levobupivacaine on neuromuscular transmission in vitro. METHODS: Thirty rats were distributed into groups (n=5) according to the drug used: ropivacaine, bupivacaine (S75-R25) and levobupivacaine. The concentration used for the three local anesthetics (LA) was 5 µg.mL.-1 The following parameters were evaluated: 1) LA effects on membrane potential (MP) and miniature end plate potential (MEPP). A chick biventer cervicis preparation was also used to evaluate LA effects on the contracture response to acetylcholine. RESULTS: LA did not alter MP values and decreased the frequency and amplitude of MEPP. In a chick biventer cervicis preparation, bupivacaine (S75-R25) and levobupivacaine decreased the contracture response to acetylcholine with statistical significance, in comparison to ropivacaine. CONCLUSIONS: In the concentrations used, levobupivacaine and bupivacaine (S75-R25) exhibited presynaptic and postsynaptic actions evidenced by alterations in miniature end plate potentials and contracture response to acetylcholine. Ropivacaine only had a presynaptic action.
Potency of Bupivacaine Stereoisomers Tested In Vitro and In Vivo
Anesthesiology, 2000
Background Chiral local anesthetics, such as ropivacaine and levobupivacaine, have the potential advantage over racemic mixtures in showing reduced toxic side effects. However, these S-(levo, or "-")isomers also have reportedly lower potency than their optical antipode, possibly resulting in no advantage in therapeutic index. Potency for local anesthetics inhibiting Na+ channels or action potentials depends on the pattern of membrane potential and so also does the stereopotency ratio. Here the authors have quantitated the stereopotencies of R-, S-, and racemic bupivacaine, comparing several in vitro assays of neuronal Na+ channels with those from in vivo functional nerve block, to establish relative potencies and to understand better the role of different modes of channel inhibition in overall functional anesthesia. Methods The binding of bupivacaine to Na+ channels was assessed indirectly by its antagonism of [3H]-batrachotoxin binding to rat brain synaptosomes. Inhibitio...
Biophysical Journal, 2008
Local anesthetics bind to ion channels in a state-dependent manner. For noninactivating voltage-gated K channels the binding mainly occurs in the open state, while for voltage-gated inactivating Na channels it is assumed to occur mainly in inactivated states, leading to an allosterically caused increase in the inactivation probability, reflected in a negative shift of the steady-state inactivation curve, prolonged recovery from inactivation, and a frequency-dependent block. How local anesthetics bind to N-type inactivating K channels is less explored. In this study, we have compared bupivacaine effects on inactivating (Shaker and K v 3.4) and noninactivating (Shaker-IR and K v 3.2) channels, expressed in Xenopus oocytes. Bupivacaine was found to block these channels time-dependently without shifting the steady-state inactivation curve markedly, without a prolonged recovery from inactivation, and without a frequency-dependent block. An analysis, including computational testing of kinetic models, suggests binding to the channel mainly in the open state, with affinities close to those estimated for corresponding noninactivating channels (300 and 280 mM for Shaker and Shaker-IR, and 60 and 90 mM for K v 3.4 and K v 3.2). The similar magnitudes of K d , as well as of blocking and unblocking rate constants for inactivating and noninactivating Shaker channels, most likely exclude allosteric interactions between the inactivation mechanism and the binding site. The relevance of these results for understanding the action of local anesthetics on Na channels is discussed.
Actions of bupivacaine, a widely used local anesthetic, on NMDA receptor responses
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2015
NMDA receptors mediate excitatory neurotransmission in brain and spinal cord and play a pivotal role in the neurological disease state of chronic pain, which is caused by central sensitization. Bupivacaine is the indicated local anesthetic in caudal, epidural, and spinal anesthesia and is widely used clinically to manage acute and chronic pain. In addition to blocking Na(+) channels, bupivacaine affects the activity of many other channels, including NMDA receptors. Importantly, bupivacaine inhibits NMDA receptor-mediated synaptic transmission in the dorsal horn of the spinal cord, an area critically involved in central sensitization. We used recombinant NMDA receptors expressed in HEK293 cells and found that increasing concentrations of bupivacaine decreased channel open probability in GluN2 subunit- and pH-independent manner by increasing the mean duration of closures and decreasing the mean duration of openings. Using kinetic modeling of one-channel currents, we attributed the obs...
Stereoselective Interactions between Local Anesthetics and Ion Channels
Chirality, 2012
Local anesthetics are useful probes of ion channel function and structure. Stereoselective interactions are especially interesting because they can reveal three-dimensional relationships between drugs and channels with otherwise identical biophysical and physicochemical properties. Furthermore, stereoselectivity suggests direct and specific receptor-mediated action, and identification of such stereospecific interactions may have important clinical consequences. The fact that drug targets are able to discriminate between the enantiomers present in a racemic drug is the consequence of the ordered asymmetric macromolecular units that form living cells. However, almost 25% of the drugs used in the clinical practice are racemic mixtures, and their individual enantiomers frequently differ in both their pharmacodynamic and pharmacokinetic profiles. Moreover, their effects can be similar to or different from the pharmacological effect of the drug and may contribute to the undesired effects of the drug. In other cases, the pharmacological effects induced by the two enantiomers on the molecular target are opposite. In the present manuscript, we will review the stereoselective effects of bupivacaine-like local anesthetics on cardiac sodium and potassium channels. Chirality 00:000-000, 2012.
Kinetic analysis of phasic inhibition of neuronal sodium currents by lidocaine and bupivacaine
Biophysical Journal, 1990
Phasic ("use-dependent") inhibition of sodium currents by the tertiary amine local anesthetics, lidocaine and bupivacaine, was observed in voltage-clamped node of Ranvier of the toad, Bufo marinus. Local anesthetics were assumed to inhibit sodium channels through occupation of a binding site with 1:1 stoichiometry. A three-parameter empirical model for state-dependent anesthetic binding to the Na channel is presented: this model includes two discrete parameters that represent the time integrals of binding and unbinding reactions during a depolarizing pulse, and one continuous parameter that represents the rate of unbinding of drug between pulses. The change in magnitude of peak sodium current during a train of depolarizing pulses to 0 mV was used as an assay of the extent of anesthetic binding at discrete intervals; estimates of model parameters were made by applying a nonlinear least-squares algorithm to the inhibition of currents obtained at two or more depolarizing pulse rates. Increasing the concentration of drug increased the rate of binding but had little or no effect on unbinding, as expected for a simple bimolecular reaction. The dependence of the model parameters on pulse duration was assessed for both drugs: as the duration of depolarizing pulses was increased, the fraction of channels binding drug during each pulse became significantly larger, whereas the fraction of occupied channels unbinding drug remained relatively constant. The rate of recovery from block between pulses was unaffected by pulse duration or magnitude. The separate contributions of open (0) and inactivated (I) channel binding of drug to the net increase in block per pulse were assessed at 0 mV: for lidocaine, the forward binding rate ko was 1.4 * 105 M-ls-1, k, was 2.4 * 104 M-1s-1; for bupivacaine, ko was 2.5-105 M-ls-1, k, was 4.4 * 104 M-ls-1. These binding rates were similar to those derived from time-dependent block of maintained Na currents in nodes where inactivation was incomplete due to treatment with chloramine-T. The dependence of model parameters on the potential between pulses (holding potential) was examined. All three parameters were found to be nearly independent of holding potential from-70 to-100 mV. These results are discussed with respect to established models of dynamic local anesthetic-Na channel interactions.
Biophysical Journal, 1990
This study assesses the importance of local anesthetic charge and hydrophobicity in determining the rates of binding to and dissociation from neuronal Na channels. Five amide-linked local anesthetics, paired either by similar PKa or hydrophobicity, were chosen for study: lidocaine, two tertiary amine lidocaine homologs, a neutral lidocaine homolog, and bupivacaine. Voltage-clamped nodes of Ranvier from the sciatic nerve of Bufo marinus were exposed to anesthetic externally, and use-dependent ("phasic") block of Na current was observed. Kinetic analysis of binding (blocking) rates was performed using a three parameter, piecewise-exponential binding model. Changes in extracellular pH (pH.) were used to assess the role of drug protonation in determining the rate of onset of, and recovery from, phasic block. For those drugs with pKa's in the range of pHo tested (6.2-10.4), the forward binding rate during a depolarizing pulse increased at higher pH, consistent with an increase in either intracellular or intramembrane concentration of drug. The rate for unbinding during depolarization was independent of pHo. The dissociation rate between pulses also increased at higher pHo. The pHo dependence of the dissociation rate was not consistent with a model in which the cation is trapped relentlessly within a closed channel. Quantitative estimates of dissociation rates show that the cationic form of lidocaine dissociates at a rate of 0.1 s-1 (at 130C); for neutral lidocaine, the dissociation rate is 7.0 s-1. Furthermore, the apparent PKa of bound local anesthetic was found to be close to the PKa in aqueous solution, but different than the PKa for '"free" local anesthetic accessible to the depolarized channel.