An in vivo Caenorhabditis elegans model for therapeutic research in human prion diseases.

Human prion diseases are fatal neurodegenerative disorders that include sporadic, infectious and genetic forms. Inherited Creutzfeldt-Jakob disease due to the E200K mutation of the prion protein-coding gene is the most common form of genetic prion disease. The phenotype resembles that of sporadic Creutzfeldt-Jakob disease at both the clinical and pathological levels, with a median disease duration of 4 months. To date, there is no available treatment for delaying the occurrence or slowing the progression of human prion diseases. Existing in vivo models do not allow high-throughput approaches that may facilitate the discovery of compounds targeting pathological assemblies of human prion protein or their effects on neuronal survival. Here, we generated a genetic model in the nematode Caenorhabditis elegans, which is devoid of any homologue of the prion protein, by expressing human prion protein with the E200K mutation in the mechanosensitive neuronal system. Expression of E200K prion protein induced a specific behavioural pattern and neurodegeneration of green fluorescent protein-expressing mechanosensitive neurons, in addition to the formation of intraneuronal inclusions associated with the accumulation of a protease-resistant form of the prion protein. We demonstrated that this experimental system is a powerful tool for investigating the efficacy of anti-prion compounds on both prion-induced neurodegeneration and prion protein misfolding, as well as in the context of human prion protein. Within a library of 320 compounds that have been approved for human use and cross the blood-brain barrier, we identified five molecules that were active against the aggregation of the E200K prion protein and the neurodegeneration it induced in transgenic animals. This model breaks a technological limitation in prion therapeutic research and provides a key tool to study the deleterious effects of misfolded prion protein in a well-described neuronal system.

Lipid nanoparticles loaded with butamben and designed to improve anesthesia at inflamed tissues.

The most frequently used local anesthetics (LA) for local infiltration have an ionizable amine in the range of pH 7.6-8.9. Effective anesthesia of inflamed tissues is a great challenge, especially because the induced local acidosis decreases the fraction of the neutral (more potent) LA species in situ. To solve this limitation, the butyl-substituted benzocaine analogue butamben (BTB) - that has no ionizable amine group close to the physiological pH - could be useful if it was not for its low solubility. To overcome the solubility problem, an optimized formulation for BTB using nanostructured lipid carriers (NLC) was developed by a factorial design and characterized using DLS, XRD, DSC and cryo-EM. The release kinetics and cytotoxicity of the new formulation were measured in vitro, while the in vivo tests assessed its effectiveness on healthy and inflamed tissues, in rats. The optimized NLCBTB formulation showed desirable physicochemical properties (size = 235.6 ± 3.9 nm, polydispersity = 0.182 ± 0.006 and zeta potential = -23.6 ± 0.5 mV), high (99.5%) encapsulation efficiency and stability during 360 days of storage at room temperature. NLCBTB prolonged the release of butamben and decreased its in vitro cytotoxicity without inducing any in vivo toxic alteration. In the inflammatory hyperalgesia model, the NLCBTB formulation showed potential for the management of inflammatory pain, displaying greater analgesic effectiveness (40%) and a prolonged effect.

Benzocaine: Review on a Drug with Unfold Potential.

Benzocaine is well-known for its role as an anesthetic agent and largely used in oral ulcers, ear pain and dental complications. Along with lidocaine and other local anesthetics, benzocaine has marked it as an anesthetic agent in surgical procedures and as Na+ channels blocker, as well. Analogues of benzocaine have been found to possess biological potentials including antibacterial, antifungal and anti-cancer. Some derivatives were found to have conspicuous action against tuberculosis. The current review focuses to explore the century-long potential of the molecule and its analogs that have appeared in the literature. Furthermore, highlighting the biological potential of benzocaine and its analogues shall open-up new dimensions of future research to design more potent analogues.

Solid and Solution State Thermodynamics of Polymorphs of Butamben (Butyl 4-Aminobenzoate) in Pure Organic Solvents.

The solubility of butamben has been measured gravimetrically in pure methanol, 1-propanol, 2-propanol, 1-butanol, and toluene over the temperature range 268-298 K. Polymorph transition and melting temperatures, associated enthalpy changes, and the heat capacity of the solid forms and the supercooled melt have been measured by differential scanning calorimetry. Based on extrapolated calorimetric data, the Gibbs energy, enthalpy and entropy of fusion, and the activity of solid butamben (the ideal solubility) have been calculated from below ambient temperature up to the melting point. Activity coefficients of butamben at equilibrium in the different solvents have been estimated from solubility data and the activity of the solid, revealing that all investigated systems exhibit positive deviation from Raoult's law. Solubility data are well correlated by a semiempirical regression model. On a mass basis, the solubility is clearly higher in methanol than in the other solvents, but mole fraction solubilities are very similar across all 5 solvents. The 2 known polymorphs are enantiotropically related, and the transition point is located at 283 K. Polymorph interconversions occur within 0.3 K of the transition point even in the solid state, and the 2 forms exhibit strong similarities in investigated properties.

Liposomal butamben gel formulations: toxicity assays and topical anesthesia in an animal model.

The aim of this study was to evaluate the in vitro cytotoxicity and the in vivo analgesic effect and local toxicity of the local anesthetic butamben (BTB) encapsulated in conventional or elastic liposomes incorporated in gel formulations. The results showed that both gel formulations of liposomal BTB reduced the cytotoxicity (p < 0.001; one-way ANOVA/Tukey's test) and increased the topical analgesic effect (p < 0.05; one-way ANOVA/Tukey's test) of butamben, compared to plain BTB gel. The gel formulations presented good rheological properties, and stability assays detected no differences in physicochemical stability up to 30 d after preparation. Moreover, histological assessment revealed no morphological changes in rat skin after application of any of the gel formulations tested.

Rationalization of reduced penetration of drugs through ceramide gel phase membrane.

Since computing resources have advanced enough to allow routine molecular simulation studies of drug molecules interacting with biologically relevant membranes, a considerable amount of work has been carried out with fluid phospholipid systems. However, there is very little work in the literature on drug interactions with gel phase lipids. This poses a significant limitation for understanding permeation through the stratum corneum where the primary pathway is expected to be through a highly ordered lipid matrix. To address this point, we analyzed the interactions of p-aminobenzoic acid (PABA) and its ethyl (benzocaine) and butyl (butamben) esters with two membrane bilayers, which differ in their fluidity at ambient conditions. We considered a dioleoylphosphatidylcholine (DOPC) bilayer in a fluid state and a ceramide 2 (CER2, ceramide NS) bilayer in a gel phase. We carried out unbiased (100 ns long) and biased z-constraint molecular dynamics simulations and calculated the free energy profiles of all molecules along the bilayer normal. The free energy profiles converged significantly slower for the gel phase. While the compounds have comparable affinities for both membranes, they exhibit penetration barriers almost 3 times higher in the gel phase CER2 bilayer. This elevated barrier and slower diffusion in the CER2 bilayer, which are caused by the high ordering of CER2 lipid chains, explain the low permeability of the gel phase membranes. We also compared the free energy profiles from MD simulations with those obtained from COSMOmic. This method provided the same trends in behavior for the guest molecules in both bilayers; however, the penetration barriers calculated by COSMOmic did not differ between membranes. In conclusion, we show how membrane fluid properties affect the interaction of drug-like molecules with membranes.

Modulation of peripheral Na(+) channels and neuronal firing by n-butyl-p-aminobenzoate.

n-butyl-p-aminobenzoate (BAB), a local anesthetic, is administered epidurally in cancer patients to treat pain that is poorly controlled by other drugs that have a number of adverse effects. The purpose of the study was to unravel the mechanisms underlying the apparent selective pain suppressant effect of BAB. We used the whole-cell patch-clamp technique to record Na(+) currents and action potentials (APs) in dissociated, nociceptive dorsal root ganglion (DRG) cells from rats, two types of peripheral sensory neuron Na(+) channels (Nav1.7 and Nav1.8), and the motor neuron-specific Na(+) channel (Nav1.6) expressed in HEK293 cells. BAB (1-100µM) inhibited, in a concentration-dependent manner, the depolarization evoked repetitive firing in DRG cells, the three types of Na(+) current expressed in HEK293 cells, and the TTXr Na(+) current of the DRG neurons. BAB induced a use-dependent block that caused a shift of the inactivation curve in the hyperpolarizing direction. BAB enhanced the onset of slow inactivation of Nav1.7 and Nav1.8 currents but not of Nav1.6 currents. At clinically relevant concentrations (1-100µM), BAB is thus a more potent inhibitor of peripheral TTX-sensitive TTXs, Nav1.7 and TTX-resistant NaV1.8 Na(+) channels than of motor neuron axonal Nav1.6 Na(+) channels. BAB had similar effects on the TTXr Na(+) channels of rat DRG neurons and Nav1.8 channels expressed in HEK293 cells. The observed selectivity of BAB in treating cancer pain may be due to an enhanced and selective responsiveness of Na(+) channels in nociceptive neurons to this local anesthetic.

Transdermal delivery of butamben using elastic and conventional liposomes.

Gel formulations containing the local anesthetic butamben (BTB) encapsulated in either conventional (BTBLUV) or elastic (BTBLUV-EL) liposomes were prepared and characterized, and then evaluated in terms of their skin permeability. Parameters measured included vesicle size and surface charge, BTB fluorescence anisotropy, encapsulation efficiency, partition coefficient and liposomal membrane organization. Encapsulation efficiencies and membrane/water partition coefficients were determined using a phase separation. The partition coefficients of the elastic and conventional formulations were 2025 ± 234 and 1136 ± 241, respectively. The sizes of the elastic and conventional liposomes did not change significantly (p > 0.05) following incorporation of the anesthetic. As expected, the elastic liposomes presented order parameters that were lower than those of the conventional liposomes, as determined by electron paramagnetic resonance with a 5-stearic acid nitroxide probe incorporated into the bilayer. After 8 h, the fluxes into the receiving solution (µg/cm(2)/h) were 6.95 ± 1.60 (10% BTB), 23.17 ± 6.09 (10% BTBLUV) and 29.93 ± 6.54 (10% BTBLUV-EL). The corresponding time lags (h) were 1.90 ± 0.48, 1.23 ± 0.28 and 1.57 ± 0.38, respectively. The permeability coefficients (10(-3 )cm/h) were 1.02 ± 0.23, 2.96 ± 0.77 and 4.14 ± 0.9, for 10% BTB, 10% BTBLUV and 10% BTBLUV-EL, respectively. The results demonstrate that anesthetic access through the skin can be considerably enhanced using liposomal gel formulations, compared to plain gel formulations.

Inhibition of sensory neuronal TRPs contributes to anti-nociception by butamben.

Butamben (n-butyl-p-aminobenzoic acid) is a pain-relieving local anesthetic for topical use. Blockade of voltage-gated channel expressed in the peripheral sensory neurons has been suggested as a mechanism of action. Its effects on another sensory neuronal channel family, transient receptor potential (TRP) have remained unclear. In this study we attempted to address this question using six sensory neuronal TRP channel-expressing heterologous systems, cultured sensory neurons and TRP-mediated acute animal pain tests. In Ca(2+) imaging and whole cell electrophysiology, TRPA1 and TRPV4 were blocked by micromolar butamben. Butamben also activated TRPA1 at millimolar concentrations. The inhibitory effects on the two TRP channels were reproducible in sensory neurons. Moreover, butamben attenuated acute animal pain behaviors in a TRPA1- or TRPV4-dependent manner. Para-aminobenzoic acid (PABA), an analog of a simpler chemical structure, displayed similar in vitro and in vivo properties, suggestive that chemical structure is important for the two TRP-specificity. Our findings suggest that inhibition of TRPA1 and TRPV4 contribute to the peripheral analgesic mechanisms of butamben.

Butamben derivatives enhance BMP-2-stimulated commitment of C2C12 cells into osteoblasts with induction of voltage-gated potassium channel expression.

As the primary step for 'drug repositioning', we evaluated the effect of 2000 drugs and drug candidates on the commitment of bi-potential mesenchymal precursor C2C12 cells into osteoblasts in the presence of bone morphogenetic protein (BMP)-2 and found that butamben enhanced BMP-2-stimulated induction of alkaline phosphatase, a biomarker of osteoblastogenesis. Investigating the underlying mechanism of its anabolic actions, we found anabolic action of its derivative (compound 4) relies on BMP-2 signaling and mRNA induction of BMPs and voltage-gated potassium channels.

New "drug-in cyclodextrin-in deformable liposomes" formulations to improve the therapeutic efficacy of local anaesthetics.

The combined approach of cyclodextrin complexation and entrapment in liposomes was investigated to develop a topical formulation of local anaesthetics. For both benzocaine (BZC) and butamben (BTM), hydroxypropyl-beta-cyclodextrin (HPbetaCD) was a better partner than betaCD; drug-HPbetaCD coevaporated products showed the best solubility and dissolution properties, and were selected for loading into liposomes. Addition of stearylamine to the phosphatidylcholine-cholesterol mixture of the vesicle bilayer allowed obtainment of deformable liposomes with improved permeation and in vivo drug anaesthetic effect (P<0.05). Double-loaded deformable liposomes were obtained by adding the drug-HPbetaCD complex at its maximum aqueous solubility in the vesicles hydrophilic phase, and the remaining amount up to 1% as free drug in the lipophilic phase. The properties of double-loaded liposomes were compared with those of classic single-loaded ones, obtained by adding 1% free drug in the aqueous or lipophilic phase of the vesicles. Size, charge, morphology and entrapment efficiency of the different batches were investigated, respectively, by light scattering, confocal laser scanning microscopy and dialysis, while their therapeutic efficacy was evaluated in vivo on rabbits. For both drugs, double-loaded liposomes, exploiting the favourable effects of drug-CD complexation, allowed a significant (P<0.05) enhancement of intensity and duration of anaesthetic effect with respect to those single-loaded.

The local anesthetic butamben inhibits total and L-type barium currents in PC12 cells.

BACKGROUND: Butamben or n-butyl-p-aminobenzoate is a long-acting experimental local anesthetic for the treatment of chronic pain when given as an epidural suspension. We have investigated whether Cav1.2/L-type calcium channels may be a target of this butamben action. METHODS: The effect of butamben on these channels was studied in undifferentiated rat PC12-cells with the whole-cell patch-clamp technique in voltage-clamp. Ba(2+) ions were used as the charge carriers in the calcium channel currents, whereas K(+) currents were removed using K(+) free solutions. RESULTS: Butamben 500 microM reversibly suppressed the total whole-cell barium current by 90% +/- 3% (n = 15), whereas 10 microM nifedipine suppressed this barium current by 75% +/- 7% (n = 6). Preexposure to butamben followed by washout decreased the inhibition by nifidepine to 47% +/- 5% (n = 10). These suppressive effects were not due to the measurement procedure and the drug vehicles in the solutions (<0.1% ethanol; n = 6). CONCLUSIONS: Butamben inhibits the total barium current through expressed calcium channel types in PC12 cells, including Cav1.2/L-type channels. Because Cav1.2 channels may also occur in human nociceptive C fibers, this result allows the possibility that these L-type channels are involved in the analgesic action of butamben.

Immobilization of paracetamol and benzocaine pro-drug derivatives as long-range self-organized monolayers on graphite.

We show here by means of scanning tunneling microscopy (STM) at the liquid/solid interface that paracetamol and benzocaine molecules bearing a long aliphatic chain can be immobilized on highly oriented pyrolitic graphite (HOPG) as perfectly ordered two-dimensional domains extending over several hundreds of nanometers. In both cases, high-resolution STM images reveal that compounds 1 and 2 self-assemble into parallel lamellae having a head-to-head arrangement. The paracetamol heads of 1 are in a zigzag position with entangled n-dodecyloxy side chains while benzocaine heads of compound 2 are perfectly aligned as a double row and have their palmitic side chains on either sides of the head alignment. We attribute the very long-range ordering of these two pro-drug derivatives on HOPG to the combined effects of intermolecular H-bonding on one side and Van der Waals interactions between aliphatic side chains and graphite on the other side. The 2D immobilization of pro-drug derivatives via a non-destructive physisorption mechanism could prove to be useful for applications such as drug delivery if it can be realized on a biocompatible substrate.

The local anesthetic butamben inhibits and accelerates low-voltage activated T-type currents in small sensory neurons.

Butamben (BAB) is a local anesthetic that can be used in epidural suspensions for long-term selective suppression of dorsal root pain signal transmission and in ointments for the treatment of skin pain. Previously, high-voltage activated N-type calcium channel inhibition has been implicated in the analgesic effect of BAB. In the present study we show that low-voltage activated or T-type calcium channels may also contribute to this effect. Typical transient T-type barium currents, selectively evoked by low-voltage (-40 mV) clamp stimulation of small (approximately 20 microm diameter) dorsal root ganglion neurons from newborn mice, were inhibited by BAB with an IC50 value of approximately 200 microM. Furthermore, 200 microM BAB accelerated T-type current activation, deactivation, and inactivation kinetics, comparable to earlier observations for N-type calcium channels. Finally, 200 microM BAB had no effect on the midpoint potential and slope factor of the activation curve, although it caused a approximately 3 mV hyperpolarizing shift of the inactivation curve, without affecting the slope factor. We conclude that BAB inhibits T-type calcium channels with a mechanism associated with channel kinetics acceleration.

Inhibition of the A-type K+ channels of dorsal root ganglion neurons by the long-duration anesthetic butamben.

n-Butyl-p-aminobenzoate (BAB; butamben) is a long-duration anesthetic used for the treatment of chronic pain. Epidural administration of BAB is thought to reduce the electrical excitability of dorsal root nociceptor fibers by inhibiting voltage-gated ion channels. To further investigate this mechanism, we examined the effects of BAB on the potassium currents of acutely dissociated neurons from the rat dorsal root ganglion (DRG). These neurons express a rapidly inactivating A-type K(+) current (I(A)) that is resistant to tetraethylammonium (20 mM) but inhibited by 4-aminopyridine (5 mM). At low concentrations, BAB (< or =1 microM) selectively inhibited the I(A) component of DRG K(+) current. The voltage dependence of activation and inactivation, kinetics of recovery from inactivation, and the pharmacology of the DRG I(A) were similar to those of the Kv4 family of K(+) channels. Reverse transcription-polymerase chain reaction was used to establish that the messages encoding for all three of the mammalian Kv4 channel subunits (Kv4.1-Kv4.3) were present in the rat DRG. BAB produced a high-affinity, partial inhibition of heterologously expressed Kv4.2 channels (K(D) = 59 nM) but did not alter the kinetics or voltage sensitivity of gating. Substituting polar threonines for conserved hydrophobic residues of the S6 segment weakened BAB binding but did not alter the voltage-dependent gating of the Kv4.2 channel. At physiological pH, BAB is uncharged, suggesting that hydrophobic interactions may contribute to drug binding. The data support a mechanism in which BAB binds near the narrow cytoplasmic entrance of Kv4 channels and inhibits current by a pore blocking mechanism.

Structural characteristics and crystal polymorphism of three local anaesthetic bases crystal polymorphism of local anaesthetic drugs: part VII.

Benzocaine (BZC), butambene (BTN) and isobutambene (BTI) are basic local anaesthetic agents of the ester type, preferentially used for surgery and dental procedures. The compounds, official in the USP (BZC and BTN) and Ph. Eur. (BZC), were each found to exist in two polymorphic crystal forms and their solid state characteristics have been determined by thermomicroscopy, differential scanning calorimetry (DSC), FTIR-, FT-Raman-spectroscopy as well as X-ray powder diffractometry. This work further emphasizes the comparison of solid state characteristics of three compounds with closely related structural features on molecular level, leading to opportunities for the investigation of structure-property relationships. Mod. I0 is the particular thermodynamically stable form at room temperature in all of the three systems. This form is present in commercial products and can be crystallized from solvents at room conditions. Mod. II can be obtained by annealing the supercooled melt or fast cooling of a saturated solution, respectively. The endothermic transformation of mod. II to mod. I0 upon heating confirms that mod. I0 is thermodynamically stable at ambient conditions (heat of transition rule) whereas mod. II is enantiotropically related to mod. I0, i.e. is metastable at temperatures above the transition temperature. The metastable forms show different kinetic stabilities at room temperature.

The block of total and N-type calcium conductance in mouse sensory neurons by the local anesthetic n-butyl-p-aminobenzoate.

To contribute to the understanding of the mechanism underlying selective analgesia by epidural application of suspensions of the local anesthetic butamben (n-butyl-p-aminobenzoate; BAB), we investigated the effect of dissolved BAB on calcium channels in sensory neurons. Small-diameter dorsal root ganglion neurons from newborn mice were used to measure whole-cell barium or calcium currents through calcium channels upon voltage-clamp stimulation. BAB suppressed the voltage-step-evoked barium current of these cells in a concentration-dependent manner with a 50% inhibitory concentration of 207 +/- 14 microM (n = 40). A similar concentration dependency was found for the pharmacologically isolated N-type component of the whole-cell barium current. The time constants of inactivation and deactivation of the N-type current became smaller in the presence of BAB, thus suggesting that kinetic changes are involved in the inhibition of this current. BAB caused a similar inhibition of the total calcium current and its N-type component when these currents were evoked by command potentials with the shape of an action potential. This inhibition of calcium currents by BAB should be considered in the search for the mechanism of selective analgesia by epidural suspensions of this local anesthetic.

Modeling of benzocaine analog interactions with the D4S6 segment of NaV4.1 voltage-gated sodium channels.

Local anesthetics (LAs) are compounds that inhibit the propagation of action potentials in excitable tissues by blocking voltage-gated Na+ channels. Mutagenesis studies have demonstrated that several amino acid residues are important sites of LA interaction with the channel, but these studies provide little information regarding the molecular forces that govern drug-binding interactions, including the binding orientation of drugs. We used computational methods to construct a simple model of benzocaine analog binding with the D4S6 segment of rat skeletal muscle (NaV4.1) sodium channels. The model revealed that four hydrophobic residues form a binding cavity for neutral LAs, and docking studies indicated that increasing hydrophobicity among the benzocaine analogs allowed a better fit within the binding cavity. The similarities between our simple model and published experimental data suggested that modeling of LA interactions with sodium channels, along with experimental approaches, could further enhance our understanding of LA interactions with sodium channels.

Analgesic synergy between topical morphine and butamben in mice.

UNLABELLED: Studies have revealed that lidocaine is an effective analgesic when applied topically to the tail of a mouse in the radiant heat tail-flick assay. In addition, the topical combination of lidocaine with morphine revealed synergistic interactions between the two drugs. In the current studies, we demonstrate that topical butamben, benzocaine, and bupivacaine are active in the radiant heat tail-flick assay. In this assay, topical lidocaine has a ceiling effect and displays a biphasic curve, with large doses markedly decreasing the responses almost to baseline levels. In contrast, butamben has an S-shape dose-dependent response in the assay and did not display a biphasic curve as seen with lidocaine, suggesting that topical butamben may have advantages over lidocaine. Both benzocaine and bupivacaine also showed dose-dependent analgesic activity in this model. Like lidocaine, butamben/morphine combinations displayed synergistic interactions. Indeed, the synergy appeared more prominent with a butamben/morphine combination. We also observed synergy between topical benzocaine and morphine. Although the bupivacaine/morphine combination was suggestive of synergy on isobolographic analysis, it did not achieve statistical significance. These studies indicate that a series of local anesthetics are all active topically in the radiant heat tail-flick assay in mice and that several interact synergistically with morphine. Of the local anesthetics tested, butamben seemed to have several pharmacological characteristics, alone and in combination with morphine, which suggest that it may be superior to the other local anesthetics. Together, these observations suggest that topical combinations of opioids and local anesthetics may prove clinically valuable. IMPLICATIONS: Topical administration of the opioid micro -agonist morphine and the sodium channel inhibitors butamben and benzocaine results in a synergistic interaction for antinociception in radiant heat tail-flick assay in mice, suggesting that the combination of these drugs will enhance rather than detract from the analgesia of either alone.

Kv1.1 channels of dorsal root ganglion neurons are inhibited by n-butyl-p-aminobenzoate, a promising anesthetic for the treatment of chronic pain.

In this study, we investigated the effects of the local anesthetic n-butyl-p-aminobenzoate (BAB) on the delayed rectifier potassium current of cultured dorsal root ganglion (DRG) neurons using the patch-clamp technique. The majority of the K(+) current of small DRG neurons rapidly activates and slowly inactivates at depolarized voltages. BAB inhibited the whole-cell K(+) current of these neurons with an IC(50) value of 228 microM. Dendrotoxin K (DTX(K)), a specific inhibitor of Kv1.1, reduced the DRG K(+) current at +20 mV by 34%, consistent with an important contribution of channels incorporating the Kv1.1 subunit to the delayed rectifier current. To further investigate the mechanism of BAB inhibition, we examined its effect on Kv1.1 channels heterologously expressed in mammalian tsA201 cells. BAB inhibits the Kv1.1 channels with an IC(50) value of 238 microM, similar to what was observed for the native DRG current. BAB accelerates the opening and closing of Kv1.1, but does not alter the midpoint of steady-state activation. BAB seems to inhibit Kv1.1 by stabilizing closed conformations of the channel. Coexpression with the Kv beta 1 subunit induces rapid inactivation and reduces the BAB sensitivity of Kv1.1. Comparison of the heterologously expressed Kv1.1 and native DRG currents indicates that the Kv beta 1 subunit does not modulate the gating of the DTX(K)-sensitive Kv1.1 channels of DRG neurons. Inhibition of the delayed rectifier current of these neurons may contribute to the long-duration anesthesia attained during the epidural administration of BAB.