Margatoxin and iberiotoxin, two selective potassium channel inhibitors, induce c-fos like protein and mRNA in rat organotypic dorsal striatal slices

The isolated single organotypic slice model allows to investigate the effects of drugs and toxins on the expression of transcription factors in the striatum without dopaminergic and glutamatergic interactions. In this study the effects of margatoxin and iberiotoxin on the expression of c-fos mRNA by in situ hybridization as well as on c-fos like protein by immunohistochemistry in isolated dorsal striatum after 10 days in culture were investigated. C-fos mRNA dose-dependently increased 30 min after incubation with margatoxin and iberiotoxin. Expression of c-fos like protein was transiently detected 3h afterwards. This effect is independent from extrinsic neuronal circuitry as dopamine neurons were found to be absent in the cultured slices. It is concluded that inhibition of voltage-gated as well as calcium-activated (Slo) potassium channels leads to activation of gene transcription in striatal neurons which may trigger long-term changes in transmitter plasticity.

Role of potassium channels in catecholamine secretion in the rat adrenal gland

We elucidated the functional contribution of K(+) channels to cholinergic control of catecholamine secretion in the perfused rat adrenal gland. The small-conductance Ca(2+)-activated K(+) (SK(Ca))-channel blocker apamin (10-100 nM) enhanced the transmural electrical stimulation (ES; 1-10 Hz)- and 1, 1-dimethyl-4-phenyl-piperazinium (DMPP; 5-40 microM)-induced increases in norepinephrine (NE) output, whereas it did not affect the epinephrine (Epi) responses. Apamin enhanced the catecholamine responses induced by acetylcholine (6-200 microM) and methacholine (10-300 microM). The putative large-conductance Ca(2+)-activated K(+) channel blocker charybdotoxin (10-100 nM) enhanced the catecholamine responses induced by ES, but not the responses induced by cholinergic agonists. Neither the K(A) channel blocker mast cell degranulating peptide (100-1000 nM) nor the K(V) channel blocker margatoxin (10-100 nM) affected the catecholamine responses. These results suggest that SK(Ca) channels play an inhibitory role in adrenal catecholamine secretion mediated by muscarinic receptors and also in the nicotinic receptor-mediated secretion of NE, but not of Epi. Charybdotoxin-sensitive Ca(2+)-activated K(+) channels may control the secretion at the presynaptic site.

Effects of voltage-gated ion channel modulators on rat prostatic cancer cell proliferation: comparison of strongly and weakly metastatic cell lines

BACKGROUND

The strongly metastatic MAT-LyLu and the weakly metastatic AT-2 rat prostatic cancer cell lines have been shown to express voltage-gated ion channels differentially. In the present study, the possible contribution of voltage-gated ion channel activity to the proliferation of these cell lines was investigated, in a comparative approach.

METHODS

Several voltage-gated ion channel modulators were tested for their effects on proliferation over 54 hr, using an in vitro assay. The modes of action of the chemicals were monitored by electrophysiological (patch-clamp) recording.

RESULTS

The voltage-gated K(+) channel blockers 4-aminopyridine (4-AP; 2 mM), margatoxin (5 nM), charybdotoxin (4.5 nM), and verapamil (50 microM) inhibited the K(+) channels of both cell lines by between 38-65% and reduced the proliferation of the AT-2 cell line, in a dose-dependent manner, by 8-51%. However, only 4-AP reduced proliferation of the MAT-LyLu cell line. Tetrodotoxin (6 microM) blocked completely the voltage-gated Na(+) channel expressed selectively in the MAT-LyLu cell line, but had no effect on the proliferation of either cell line. On the other hand, the presumed Na(+) channel "opener" veratridine (10-50 microM) reduced significantly, in a dose-dependent manner, the proliferation of both cell lines by up to approximately 30%.

CONCLUSIONS

We conclude that the mechanism(s) controlling the proliferation of the weakly metastatic AT-2 cells involves voltage-gated K(+) channels. In contrast, the proliferation of strongly metastatic MAT-LyLu cells is much less dependent upon voltage-gated K(+) channel activity.

Electrophysiological characterization of voltage-gated K(+) currents in cerebellar basket and purkinje cells: Kv1 and Kv3 channel subfamilies are present in basket cell nerve terminals

To understand the processes underlying fast synaptic transmission in the mammalian CNS, we must have detailed knowledge of the identity, location, and physiology of the ion channels in the neuronal membrane. From labeling studies we can get clues regarding the distribution of ion channels, but electrophysiological methods are required to determine the importance of each ion channel in CNS transmission. Dendrotoxin-sensitive potassium channel subunits are highly concentrated in cerebellar basket cell nerve terminals, and we have previously shown that they are responsible for a significant fraction of the voltage-gated potassium current in this region. Here, we further investigate the characteristics and pharmacology of the voltage-dependent potassium currents in these inhibitory nerve terminals and compare these observations with those obtained from somatic recordings in basket and Purkinje cell soma regions. We find that alpha-DTX blocks basket cell nerve terminal currents and not somatic currents, and the IC(50) for alpha-DTX in basket cell terminals is 3.2 nM. There are at least two distinct types of potassium currents in the nerve terminal, a DTX-sensitive low-threshold component, and a second component that activates at much more positive voltages. Pharmacological experiments also reveal that nerve terminal potassium currents are also markedly reduced by 4-AP and TEA, with both high-sensitivity (micromolar) and low-sensitivity (millimolar) components present. We suggest that basket cell nerve terminals have potassium channels from both the Kv1 and Kv3 subfamilies, whereas somatic currents in basket cell and Purkinje cell bodies are more homogeneous.

Incidence of immediate and delayed hypersensitivity to Centruroides antivenom

STUDY OBJECTIVE

To assess the incidence and course of immediate and delayed hypersensitivity to Centruroides antivenom.

METHODS

We performed a 12-month prospective observation study, with telephone follow-up, evaluating the incidence of anaphylaxis or anaphylactoid reactions and serum sickness after Centruroides antivenom administration. The setting for the study was a poison control center and tertiary care toxicology treatment center. Participants included all patients who received Centruroides antivenom, and no interventions were performed.

RESULTS

For immediate hypersensitivity reactions, 116 patients with grade III or IV envenomation received Centruroides antivenom; 77 of these patients were younger than 13 years. Three patients completed the infusion despite development of rash. A fourth patient with a history of atopy and asthma received epinephrine infusion and an inhaled beta-agonist for transient wheezing that quickly resolved; she was admitted for observation. Nine patients without hypersensitivity reactions were admitted for social reasons, for inappropriate sedation from drugs used before antivenom, or to rule out aspiration; all were discharged within 24 hours. The remaining 106 patients were discharged from the emergency department after resolution of symptoms. Thus 4 of 116 patients had immediate reactions. For patients with delayed reactions, 17 patients were lost to follow-up. Of 99 remaining patients, serum sickness developed in 61% (n=60), as defined by using liberal criteria. Serum sickness responded to oral steroids, antihistamines, or both; mean duration of symptoms with medication was 2.8 days.

CONCLUSION

Anaphylactic reactions are uncommon after Centruroides antivenom infusion. Self-limited serum sickness that is easily controlled with corticosteroids and antihistamines commonly follows the use of Centruroides antivenom.

The pharmacological flexibility of the insect voltage gated sodium channel: toxicity of AaIT to knockdown resistant (kdr) flies

AaIT is an insect selective neurotoxic polypeptide shown to affect insect neuronal sodium conductance by binding to excitable sodium channels. In the present study the paralytic potency of AaIT to wild type and various mutant strains of houseflies (Musca domestica) and fruitflies (Drosophila melanogaster) was examined and it has been shown that: On the basis of body weight when compared to published data on Sarcophaga falculata blowflies, the Musca and Drosophila flies reveal at least two orders of magnitude decreased susceptibility to the AaIT. When compared to wild type flies the toxicity of AaIT is greatly altered in knockdown resistant fly strains which are mutated in their para gene encoding the voltage gated sodium channel. Several strains, with genetically mapped para mutations conferring pyrethroid resistance, exhibited opposing response to AaIT. The para ts2 Drosophila strain, with a point of mutation in domain I of the para gene conferring a 6-fold resistance to deltamethrin also showed about 15-fold tolerance to AaIT. On the other hand the Musca kdr and super-kdr flies, with a single or a double point mutation, respectively in domain II of the para gene, are about 9- and 14-fold more susceptible to AaIT, respectively. The above data are interpreted in terms of the pharmacological diversity and flexibility ("allosteric coupling") of voltage gated sodium channels and their implications for the management of pesticide resistance are discussed.

Effects of tachykinin NK1 or PAF receptor blockade on the lung injury induced by scorpion venom in rats

In cases of severe human scorpion envenoming, lung injury is a common finding and frequently the cause of death. In the rat, two distinct mechanisms account for oedema following the intravenous injection of the venom -- acute left ventricular failure resulting from a massive release of catecholamines and an increase in pulmonary vascular permeability. In the present work, we investigated the effects of a tachykinin NK1 receptor antagonist (CP96,345, the dihydrochloride salt of (2S,3S)-cis-2-(diphenylmethyl)-N-((2-methoxyphenyl)methyl)-1-az abicycol[2.2.2]octan-3-amine) and its 2 R-3 R inactive enantiomer (CP96,344) on the acute lung injury induced by the i.v. injection of Tityus serrulatus venom in rats. Lung injury was assessed by evaluating the extravasation of Evans blue dye in the bronchoalveolar lavage fluid and in the lung of venom-treated and control animals. The effects of the platelet-activating factor (PAF) receptor antagonist WEB2170 (2-methyl-1-phenylimidazol[4,5c]pyridine) were evaluated for comparison. The i.v. injection of the venom induced the extravasation of Evans blue in the bronchoalveolar lavage fluid and into the left lung. Pretreament with the tachykinin NK1 receptor antagonist CP96,345, but not CP96,344, inhibited Evans blue dye extravasation in the bronchoalveolar lavage fluid and in the lung by 96% and 86%, respectively. The PAF receptor antagonist WEB2170 inhibited the increase in vascular permeability in the bronchoalveolar lavage fluid by 60% and had no effect on the extravasation to the lung parenchyma of venom-injected animals. In addition to abrogating lung injury, pretreatment of rats with CP96,345, but not CP96,344 or WEB2170, decreased by 70% the mortality induced by the venom. This is the first study to show the relevance of the tachykinin NK1 receptor in mediating lung injury and mortality in animals injected with the neurotoxic T. serrulatus venom. Blockade of the tachykinin NK1 receptor may represent an important strategy in the treatment of patients with signs of severe envenoming and clearly deserves further studies.

Induction of potassium channels in mouse brain microglia: cells acquire responsiveness to pneumococcal cell wall components during late development

Lipopolysaccharides derived from cell walls of Gram-negative bacteria have proven a useful tool to simulate bacterial infection of the central nervous system. Rapid activation of microglia within the brain parenchyma as well as in vitro has thereby been shown to be an early event upon bacterial or lipopolysaccharide challenges. Less is known about microglial responses to a contact with Gram-positive bacteria, such as Streptococcus pneumoniae, a lethal pathogen causing meningitis with a 30% mortality rate. In the present study, we compared lipopolysaccharide-induced microglial activation in vitro with that induced by preparations of pneumococcal cell walls. As a readout of microglial activation, we studied by patch-clamp recording the expression of outward rectifying potassium currents (IK+OR), which are known to be induced by lipopolysaccharide. We found that pneumococcal cell walls and lipopolysaccharide induced a similar type of IK+OR. Stimulation of IK+OR by pneumococcal cell walls and lipopolysaccharide involved protein synthesis since it was not induced in the presence of cycloheximide. Pharmacological characterization of the pneumococcal cell wall- and lipopolysaccharide-induced currents with specific ion channel blockers indicated for both cases expression of the charybdotoxin/margatoxin-sensitive Kv1.3 subtype of the Shaker family of voltage-dependent potassium channels. Activation of the outward currents by pneumococcal cell walls depended on the developmental stage: while lipopolysaccharide triggered IK+OR in both embryonal and postnatal microglial cells, pneumococcal cell walls had only a marginal effect on embryonal cells. This, however, does not imply that embryonic microglial cells are unresponsive to pneumococcal cell walls. In both embryonic and postnatal cells, (i) the amplitude of the constitutively expressed inward rectifying potassium current was significantly reduced, (ii) tumor necrosis factor-a was released and (iii) the cells changed their morphology, similarly as it was induced by lipopolysaccharide treatment. Thus, embryonic microglial cells are sensitive to pneumococcal cell wall challenges, but respond with a distinctly different pattern of physiological reactions. The expression of IK+OR could thus be a suitable tool to study signalling cascades selectively involved in the activation of microglia by Gram-negative and -positive cell wall components and to functionally distinguish between populations of microglial cells.

Effects of ATP and elevated K+ on K+ currents and intracellular Ca2+ in human microglia

We have used whole-cell patch-clamp recordings and calcium microfluorescence measurements to study the effects of ATP and elevated external K+ on properties of human microglia. The application of ATP (at 0.1 mM) led to the activation of a transient inward non-selective cationic current at a cell holding potential of -60 mV and a delayed, transient expression of an outward K+ current activated with depolarizing steps applied from holding level. The ATP response included an increase in inward K+ conductance and a depolarizing shift in reversal potential as determined using a voltage ramp waveform applied from -120 to -50 mV. Fura-2 microspectrofluorescence measurements showed intracellular calcium to be increased following the application of ATP. This response was characterized by an initial transient phase, which persisted in Ca2+-free media and was due to release of Ca2+ from intracellular storage sites. The response had a later plateau phase, consistent with Ca2+ influx. In addition, ATP-induced changes in intracellular Ca2+ exhibited prominent desensitization. Elevated external K+ (at 40 mM) increased inward K+ conductance and shifted the reversal potential in the depolarizing direction, with no effect on outward K+ current or the level of internal Ca2+. The results of these experiments show the differential responses of human microglia to ATP and elevated K+, two putative factors associated with neuronal damage in the central nervous system.

Government-owned inventions; availability for licensing. National Institutes of Health, Public Health Service, DHHS. Notice

The inventions listed below are owned by agencies of the U.S. Government and are available for licensing in the U.S. in accordance with 35 U.S.C. 207 to achieve expeditious commercialization of results of federally-funded research and development. Foreign patent applications are filed on selected inventions to extend market coverage for companies and may also be available for licensing.

Crystallization and preliminary diffraction data of neurotoxin Ts-gamma from the venom of the scorpion Tityus serrulatus

Scorpion neurotoxin Ts-gamma was isolated from Tityus serrulatus venom and purified to apparent homogeneity by ion-exchange HPLC. Crystals of the toxin were grown using polyethylene glycol 6000 as precipitant and were found to belong to the monoclinic space group P21 with cell parameters a = 22.20, b = 36.90, c = 31.57 A, beta = 100.85 degrees. The crystals diffract beyond 1.73 A resolution at a synchrotron beamline, being notably stable during X-ray exposure. The structure has been solved by molecular replacement using the very high resolution structure of Sahara scorpion Androctonus australis Hector (PDB code 1AHO) as a search model.

Actions of scorpion venom on skeletal muscle

A protein-like constituent of scorpion venom produced effects on the skeletal muscle fibre resembling those of citrate, lack of calcium or veratrine. These effects could be diminished by the addition of calcium. They do not appear to be due to the formation of a non-ionized complex with calcium.

Characterization of the cloned human intermediate-conductance Ca2+-activated K+ channel

The human intermediate-conductance, Ca2+-activated K+ channel (hIK) was identified by searching the expressed sequence tag database. hIK was found to be identical to two recently cloned K+ channels, hSK4 and hIK1. RNA dot blot analysis showed a widespread tissue expression, with the highest levels in salivary gland, placenta, trachea, and lung. With use of fluorescent in situ hybridization and radiation hybrid mapping, hIK mapped to chromosome 19q13.2 in the same region as the disease Diamond-Blackfan anemia. Stable expression of hIK in HEK-293 cells revealed single Ca2+-activated K+ channels exhibiting weak inward rectification (30 and 11 pS at -100 and +100 mV, respectively). Whole cell recordings showed a noninactivating, inwardly rectifying K+ conductance. Ionic selectivity estimated from bi-ionic reversal potentials gave the permeability (PK/PX) sequence K+ = Rb+ (1.0) > Cs+ (10.4) >> Na+, Li+, N-methyl-D-glucamine (>51). NH+4 blocked the channel completely. hIK was blocked by the classical inhibitors of the Gardos channel charybdotoxin (IC50 28 nM) and clotrimazole (IC50 153 nM) as well as by nitrendipine (IC50 27 nM), Stichodactyla toxin (IC50 291 nM), margatoxin (IC50 459 nM), miconazole (IC50 785 nM), econazole (IC50 2.4 microM), and cetiedil (IC50 79 microM). Finally, 1-ethyl-2-benzimidazolinone, an opener of the T84 cell IK channel, activated hIK with an EC50 of 74 microM.

Single-channel characterization of the pharmacological properties of the K(Ca2+) channel of intermediate conductance in bovine aortic endothelial cells

The pharmacological profile of a voltage-independent Ca2+-activated potassium channel of intermediate conductance (IK(Ca2+)) present in bovine aortic endothelial cells (BAEC) was investigated in a series of inside-out and outside-out patch-clamp experiments. Channel inhibition was observed in response to external application of ChTX with a half inhibition concentration of 3.3 +/- 0.3 nm (n = 4). This channel was insensitive to IbTX, but channel block was detected following external application of MgTX and StK leading to the rank order toxin potency ChTX > StK > MgTX >>IbTX. A reduction of the channel unitary current amplitude was also measured in the presence of external TEA, with half reduction occurring at 23 +/- 3 mm TEA (n = 3). The effect of TEA was voltage insensitive, an indication that TEA may bind to a site located on external side of the pore region of this channel. Similarly, the addition of d-TC to the external medium caused a reduction of the channel unitary current amplitude with half reduction at 4.4 +/- 0.3 mm (n = 4). In contrast, application of d-TC to the bathing medium in inside-out experiments led to the appearance of long silent periods, typical of a slow blocking process. Finally, the IK(Ca2+) in BAEC was found to be inhibited by NS1619, an activator of the Ca2+-activated potassium channel of large conductance (Maxi K(Ca2+)), with a half inhibition value of 11 +/- 0.8 micron (n = 4). These results provide evidence for a pharmacological profile distinct from that reported for the Maxi K(Ca2+) channel, with some features attributed to the voltage-gated KV1.2 potassium channel.

Margatoxin increases dopamine release in rat striatum via voltage-gated K+ channels

The distribution of iodinated margatoxin ([125I]margatoxin) binding sites in rat was investigated by autoradiography. Rat striatum expresses a high density of margatoxin binding sites and, therefore, the effects of margatoxin, charybdotoxin and iberiotoxin have been studied on [3H]dopamine release from rat striatal slices in vitro. Margatoxin (0.1-100 nM) and charybdotoxin (10-1000 nM), but not iberiotoxin increased the spontaneous and the electrically evoked [3H]dopamine release. [3H]dopamine release by margatoxin was inhibited by tetrodotoxin and omega-conotoxin GVIA, but not by atropine, naloxone, N(omega)-nitro-L-arginine and neurokinin or neurotensin receptor antagonists. In the buffer solution used for release experiments, [125I]margatoxin labels a maximum of 0.12 pmol of sites/mg protein in rat striatal membranes with a Kd of 5 pM. [125I]margatoxin binding was inhibited by margatoxin (Ki of 4 pM), charybdotoxin (Ki of 162 pM) but not by iberiotoxin. We conclude that inhibition of margatoxin-sensitive voltage-gated K+ channels increases [3H]dopamine release demonstrating their role in repolarization of nigrostriatal projections. In contrast, iberiotoxin-sensitive, high-conductance Ca2+-activated K+ channels are not involved in release of [3H]dopamine.

Complex subunit assembly of neuronal voltage-gated K+ channels. Basis for high-affinity toxin interactions and pharmacology

Neurons require specific patterns of K+ channel subunit expression as well as the precise coassembly of channel subunits into heterotetrameric structures for proper integration and transmission of electrical signals. In vivo subunit coassembly was investigated by studying the pharmacological profile, distribution, and subunit composition of voltage-gated Shaker family K+ (Kv1) channels in rat cerebellum that are labeled by 125I-margatoxin (125I-MgTX; Kd, 0.08 pM). High-resolution receptor autoradiography showed spatial receptor expression mainly in basket cell terminals (52% of all cerebellar sites) and the molecular layer (39% of sites). Sequence-directed antibodies indicated overlapping expression of Kv1. 1 and Kv1.2 in basket cell terminals, whereas the molecular layer expressed Kv1.1, Kv1.2, Kv1.3, and Kv1.6 proteins. Immunoprecipitation experiments revealed that all 125I-MgTX receptors contain at least one Kv1.2 subunit and that 83% of these receptors are heterotetramers of Kv1.1 and Kv1.2 subunits. Moreover, 33% of these Kv1.1/Kv1.2-containing receptors possess either an additional Kv1.3 or Kv1.6 subunit. Only a minority of the 125I-MgTX receptors (<20%) seem to be homotetrameric Kv1.2 channels. Heterologous coexpression of Kv1.1 and Kv1.2 subunits in COS-1 cells leads to the formation of a complex that combines the pharmacological profile of both parent subunits, reconstituting the native MgTX receptor phenotype. Subunit assembly provides the structural basis for toxin binding pharmacology and can lead to the association of as many as three distinct channel subunits to form functional K+ channels in vivo.

Dopaminergic properties of cultured rat carotid body chemoreceptors grown in normoxic and hypoxic environments

Using dissociated carotid body (CB) cultures prepared from neonatal (postnatal days 5-7; P7) or juvenile (postnatal day 19-20; P20) rats, we compared catecholaminergic properties and mechanisms of O2 sensing in glomus cells grown in normoxic (Nox; 20% O2) and chronically hypoxic (CHox; 6% O2) environments for up to 2 weeks. In Nox cultures, basal dopamine (DA) release, determined by HPLC and normalized to the number of tyrosine hydroxylase-positive glomus cells present, was similar for P7 and P20 cultures (approximately 0.3 pmol/1,000 cells/15 min) and was unaffected by culture duration (2 vs. 12 days). Acute hypoxia (5 and 10% O2) caused a dose-dependent stimulation (6x and 3x basal, respectively) in DA release, that was inhibited by nifedipine (10 microM). DA release was also stimulated by high extracellular K+ (30 mM) and iberiotoxin (200 nM), a selective blocker of PO2-regulated, Ca-dependent K+ channel in glomus cells. The stimulatory effect of iberiotoxin was similar to 5% O2 in P20 cultures, but substantially less (about one-half) in P7 cultures. In contrast, in CHox cultures, basal DA release was substantially elevated, approximately 8x Nox levels, although this did not correlate with significant differences in stores. Further, whereas acute hypoxia (5% O2) and high K+ also stimulated DA release in CHox cultures (approximately 2x and approximately 3x basal), iberiotoxin (200 nM) did not. Thus, after chronic hypoxia in vitro, there is an enhanced basal catecholamine release and an apparent down-regulation of functional Ca-dependent K+ channels in CB chemoreceptors. These cellular adaptations may relate to changes in CB chemosensitivity during chronic hypoxemia.

Molecular modeling of voltage-gated potassium channel pore

AIM

To build a structure model for the pore of voltage-gated Shaker potassium channel and examine its validity.

METHODS

(1) Structural restraints were derived from experimental and theoretical studies; (2) An initial structural motif satisfying the derived restraints was first constructed, and further refined by restrained molecular mechanics; (3) The quality of the model was judged by the criterion that whether it could clarify molecular mechanisms of channel functions and explain the known experimental facts.

RESULTS

(1) A computer pore structure was proposed, in which the residues within signature sequence (corresponding to Shaker 439-446) dipped into the membrane and formed the narrow part of the pore in a non-periodic conformation, while the other residues in the P region constituted the outer mouth of the pore; (2) The ion selectivity was achieved through cation-pi orbital interaction mechanism at position 445 and oxygen cage mechanism at position 447; (3) Different binding modes led to different affinity of CTX and AgTx2 to channel; and (4) The inside of pore was dominated by negative electrostatic potential.

CONCLUSION

The model proposed was consistent with the derived restraints from the experimental results.

Blockade of the voltage-gated potassium channel Kv1.3 inhibits immune responses in vivo

The voltage activated K+ channel (Kv1.3) has recently been identified as the molecule that sets the resting membrane potential of peripheral human T lymphoid cells. In vitro studies indicate that blockage of Kv1.3 inhibits T cell activation, suggesting that Kv1.3 may be a target for immunosuppression. However, despite the in vitro evidence, there has been no in vivo demonstration that blockade of Kv1.3 will attenuate an immune response. The difficulty is due to species differences, as the channel does not set the membrane potential in rodent peripheral T cells. In this study, we show that the channel is present on peripheral T cells of miniswine. Using the peptidyl Kv1.3 inhibitor, margatoxin, we demonstrate that Kv1.3 also regulates the resting membrane potential, and that blockade of Kv1.3 inhibits, in vivo, both a delayed-type hypersensitivity reaction and an Ab response to an allogeneic challenge. In addition, prolonged Kv1.3 blockade causes reduced thymic cellularity and inhibits the thymic development of T cell subsets. These results provide in vivo evidence that Kv1.3 is a novel target for immunomodulation.