Differential modulation of Na v 1.7 and Na v 1.8 peripheral nerve sodium channels by the local anesthetic lidocaine (original) (raw)
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British Journal of Pharmacology, 2004
1 The interaction of lidocaine-like local anaesthetics with voltage-operated sodium channels is traditionally assumed to be characterized by tighter binding of the drugs to depolarized channels. As inactivated and drug-bound channels are both unavailable on depolarization, an indirect approach is required to yield estimates for the dissociation constants from channels in inactivated states. The established model, originally described by Bean et al., describes the difference in affinity between resting and inactivated states in terms of the concentration dependence of the voltage shift in the availability curve. We have tested the hypothesis that this model, which assumes a simple Langmuir relationship, could be improved by introducing a Hill-type exponent, which would take into account potential sources of cooperativity.
Journal of Neurophysiology, 2007
Nociceptive neurons of the dorsal root ganglion (DRG) express a combination of rapidly gating TTX-sensitive and slowly gating TTX-resistant Na currents, and the channels that produce these currents have been cloned. The Nav1.7 and Nav1.8 channels encode for the rapidly inactivating TTX-sensitive and slowly inactivating TTX-resistant Na currents, respectively. Although the Nav1.7 channel expresses well in cultured mammalian cell lines, attempts to express the Nav1.8 channel using similar approaches has been met with limited success. The inability to heterologously express Nav1.8 has hampered detailed characterization of the biophysical properties and pharmacology of these channels. In this study, we investigated the determinants of Nav1.8 expression in tsA201 cells, a transformed variant of HEK293 cells, using a combination of biochemistry, immunochemistry, and electrophysiology. Our data indicate that the unusually low expression levels of Nav1.8 in tsA201 cells results from a traff...
Molecular Pharmacology, 2005
The interaction of symmetrical lidocaine dimers with voltagegated Na ϩ channels (VGSCs) was examined using a FLIPR membrane potential assay and voltage-clamp. The dimers, in which the tertiary amines of the lidocaine moieties are linked by an alkylene chain (two to six methylene units), inhibited VGSC activator-evoked depolarization of cells heterologously-expressing rat (r) Na v 1.2a, human (h) Na v 1.5, and rNa v 1.8, with potencies 10-to 100-fold higher than lidocaine (compound 1). The rank order of potency (C 4 (compound 4) Ͼ C 3 (compound 3) Ն C 2 (compound 2) ϭ C 5 (compound 5) ϭ C 6 (compound 6) Ͼ Ͼ compound 1) was similar at each VGSC. Compound 4 exhibited strong use-dependent inhibition of hNa v 1.5 with pIC 50 values Ͻ4.5 and 6.0 for tonic and phasic block, respectively. Coincubation with local anesthetics but not tetrodotoxin attenuated compound 4-mediated inhibition of hNa v 1.5. These
Journal of General Physiology, 1996
A B S T RA C T We have recently reported that brain sodium channels display periods with high (low-/Q) and low (high-/Q) levels of lidocaine-induced open channel block (Salazar, B.C., D.O. Flash, J.L. Walewski, and E. Recio-Pinto. 1995. Brain Res. 699:305-314). In the present study, we further characterize this phenomenon by studying the effects of the permanently charged lidocaine analogue, QX-314. We found that the detection of high-and low-/Q periods does not require the presence of the uncharged form of lidocaine. The level of block, for either period, at various QX-314 concentrations indicated the presence of a single local anesthetic binding site. Increasing the concentration of QX-314 decreased the lifetime of the high-/Q periods while it increased the lifetime of the low-/Q periods. These results could be best fitted to a model with two open channel conformations that display different local anesthetic Kd values (low and high/Q), and in which the channel area defining the local anesthetic/Q consists of multiple interacting regions. Amplitude distribution analysis showed that changes in the/Q values reflected changes in the kon rates, without changes in the kof f rates. Both lidocaine and QX-314 were found to be incapable of blocking small-channel subconductance states (5-6 pS). Changes in the local anesthetic kon rates for blocking the fully open state and the lack of local anesthetic block of the small subconductance state are consistent with the presence of channel conformational changes involving the intracellular permeation pathway leading to the local anesthetic binding site. Key words: lidocaine 9 QX-314 9 brain voltage-dependent sodium channels 9 open channel block
British Journal of Pharmacology, 2002
1 The structural features that determine the state-dependent interaction of local anaesthetics with voltage-operated sodium channels are still a matter of debate. We have studied the blockade of sodium channels by 2,6-dimethylphenol, a phenol derivative which resembles the aromatic tail of lidocaine, etidocaine, and bupivacaine. 2 The eects of 2,6-dimethylphenol were studied on heterologously (HEK 293) expressed rat neuronal (rat brain IIA) and human skeletal muscle (hSkM1) sodium channels using whole-cell voltage-clamp experiments. 3 2,6-Dimethylphenol was eective in blocking whole-cell sodium inward currents. Its potency was comparable to the potency of lidocaine previously obtained with similar protocols by others. The IC 50 at 770 mV holding potential was 150 and 187 mM for the skeletal muscle and the neuronal isoform, respectively. In both isoforms, the blocking potency increased with the fraction of inactivated channels at depolarized holding potentials. However, the block achieved at 770 mV with respect to 7150 mV holding potential was signi®cantly higher only in the skeletal muscle isoform. The estimated dissociation constant K d from the inactivated state was 25 mM and 28 mM in the skeletal muscle and the neuronal isoform, respectively. The kinetics of drug equilibration between resting and inactivated channel states were about 10 fold faster compared with lidocaine. 4 Our results show that the blockade induced by 2,6-dimethylphenol retains voltage-dependency, a typical feature of lidocaine-like local anaesthetics. This is consistent with the hypothesis that thè aromatic tail' determines the state-dependent interaction of local anaesthetics with the sodium channel.
In vivo potency of different ligands on voltage-gated sodium channels
European Journal of Pharmacology, 2015
The Ranvier nodes of thick myelinated nerve fibers contain almost exclusively voltage-gated sodium channels (Na v s), while the unmyelinated fibers have several receptors (e.g., cannabinoid, transient receptor potential vanilloid receptor 1), too. Therefore, a nerve which contains only motor fibers can be an appropriate in vivo model for selective influence of Na v s. The goals were to evaluate the potency of local anesthetic drugs on such a nerve in vivo; furthermore, to investigate the effects of ligands with different structures (arachidonic acid, anandamide, capsaicin and nisoxetine) that were proved to inhibit Na v s in vitro with antinociceptive properties. The marginal mandibular branch of the facial nerve was explored in anesthetized Wistar rats; after its stimulation, the electrical activity of the vibrissae muscles was registered following the perineural injection of different drugs. Lidocaine, bupivacaine and ropivacaine evoked dose-dependent decrease in electromyographic activity, i.e., lidocaine had lower potency than bupivacaine or ropivacaine. QX-314 did not cause any effect by itself, but its co-application with lidocaine produced a prolonged inhibition. Nisoxetine had a very low potency. While anandamide and capsaicin in high doses caused about 50% decrease in the amplitude of action potential, arachidonic acid did not influence the responses. We proved that the classical local anesthetics have high potency on motor nerves, suggesting that this method might be a reliable model for selective targeting of Navs in vivo circumstances. It is proposed that the effects of these endogenous lipids and capsaicin on sensory fibers are not primarily mediated by Navs.
Interactions between quaternary lidocaine, the sodium channel gates, and tetrodotoxin
Biophysical Journal, 1979
ABSTRACr A voltage clamp technique was used to study sodium currents and gating currents in squid axons internally perfused with the membrane impermeant sodium channel blocker, QX-3 14. Block by QX-3 14 is strongly and reversibly enhanced if a train of depolarizing pulses precedes the measurement. The depolarization-induced block is antagonized by external sodium. This antagonism provides evidence that the blocking site for the drug lies inside the channel. Depolarization-induced block of sodium current by QX-314 is accompanied by nearly twofold reduction in gating charge movement. This reduction does not add to a depolarizationinduced immobilization of gating charge normally present and believed to be associated with inactivation of sodium channels. Failure to act additively suggests that both, inactivation and QX-314, affect the same component of gating charge movement. Judged from gating current measurements, a drug-blocked channel is an inactivated channel. In the presence of external tetrodotoxin and internal QX-314, gating charge movement is always half its normal size regardless of conditioning, as if QX-3 14 is then permanently present in the channel.
Blockade of cardiac sodium channels by lidocaine. Single-channel analysis
Circulation research, 1989
Hie mechanism of interaction of lidocaine with cardiac sodium channels during use-dependent block is not well denned. We examined the blockade of single cardiac sodium channels by lidocaine and its hydrophobic derivative RAD-242 in rabbit ventricular myocytes. Experiments were performed in cell-attached and inside-out patches. Use-dependent block was assessed with trains of ten 200 -msec pulses with interpulse intervals of 500 msec and test potentials of -60 to -40 mV. Single-channel kinetics sometimes showed time-dependent change in the absence of drug. During exposure to 80 /iM lidocaine, use-dependent block during the trains was associated with a decrease in the average number of openings per step. At -60 mV, mean open time was not significantly changed (control, 1.4±0.6 msec; lidocaine, 1.2±03 msec, p>0.05). Greater block developed during trains of 200 -msec pulses compared with trains of 20-msec pulses at the same interpulse interval at test potentials during which openings were uncommon later than 20 msec (-50 and -40 mV). Prolonged bursts of channels showing slow-gating kinetics were observed both in control and the presence of 80 /iM lidocaine. However, lidocaine may decrease the late sodium current by altering the kinetics of slow gating. The hydrophobic lidocaine derivative RAD-242, which has a 10-fold greater lipid solubility than lidocaine, decreased the peak averaged current during pulse train stimulation by 60% without a change in the mean open time. Our results suggest that the major effect of lidocaine during use-dependent block involves the interaction with a nonconducting state of the sodium channel followed by a failure to open during subsequent depolarization. {Circulation Research 1989;65:1247-1262 L idocaine is the antiarrhythmic drug most frequently used for prophylaxis and treatment of postinfarction ventricular arrhythmias. The antiarrhythmic effects are exerted at concentrations 1/100 or less of that required to block the nerve action potential. 1 -2 In both tissues, the drug is believed to exert its effect by blockade of the inward sodium current (I Na ). 3 ' 4 Upstroke velocity and macroscopic current measurements have shown that block is strongly dependent on the rate and pattern of stimulation. 4 The patterns of blockade have been interpreted by models based on variations of affinity with voltage-dependent channel state or of state-dependent access of drug to its binding site. 3 -5 Recent ligand-binding studies suggest the presence of a stereospecific binding site for lidocaine and other antiarrhythmic drugs on the sodium channel protein. 6 ' 7 Whole-cell I N , and binding studies do not provide direct information about the binding of the drug to defined states of the channel and the relative potencies of intracellular and extracellular drug application. Recent recording of single sodium channel current in cardiac myocytes offer a number of possibilities for analysis of the molecular basis of the blocking action of lidocaine. 8 -12 The probability that a channel may open in response to depolarization, the amplitude of the current of a single channel at a given test voltage (conductance), and the distribution of channel open times can all be measured directly. Known concentrations of drug can be applied to either the intracellular or extracellular membrane surface. The whole-cell sodium current is related to the underlying single channel events according to the equation: I Nl =AT o i, where N is the number of channels, P o is the probability of a channel being open, and i is the unitary current of a sodium channel. Therefore, during use-dependent inhibition, lidocaine and other antiarrhythmic drugs may reduce I N , by a reduction of N, of P o , of i, or of