Dendritic A-type potassium channel subunit expression in CA1 hippocampal interneurons

Voltage-gated potassium (Kv) channels are important and diverse determinants of neuronal excitability and exhibit specific expression patterns throughout the brain. Among Kv channels, Kv4 channels are major determinants of somatodendritic A-type current and are essential in controlling the amplitude of backpropagating action potentials (BAPs) into neuronal dendrites. BAPs have been well studied in a variety of neurons, and have been recently described in hippocampal and cortical interneurons, a heterogeneous population of GABAergic inhibitory cells that regulate activity of principal cells and neuronal networks. We used well-characterized mouse monoclonal antibodies against the Kv4.3 and potassium channel interacting protein (KChIP) 1 subunits of A-type Kv channels, and antibodies against different interneuron markers in single- and double-label immunohistochemistry experiments to analyze the expression patterns of Kv4.3 and KChIP1 in hippocampal Ammon's horn (CA1) neurons. Immunohistochemistry was performed on 40 mum rat brain sections using nickel-enhanced diaminobenzidine staining or multiple-label immunofluorescence. Our results show that Kv4.3 and KChIP1 component subunits of A-type channels are co-localized in the soma and dendrites of a large number of GABAergic hippocampal interneurons. These subunits co-localize extensively but not completely with markers defining the four major interneuron subpopulations tested (parvalbumin, calbindin, calretinin, and somatostatin). These results suggest that CA1 hippocampal interneurons can be divided in two groups according to the expression of Kv4.3/KChIP1 channel subunits. Antibodies against Kv4.3 and KChIP1 represent an important new tool for identifying a subpopulation of hippocampal interneurons with a unique dendritic A-type channel complement and ability to control BAPs.     

Altered expression and localization of hippocampal A-type potassium channel subunits in the pilocarpine-induced model of temporal lobe epilepsy

Altered ion channel expression and/or function may contribute to the development of certain human epilepsies. In rats, systemic administration of pilocarpine induces a model of human temporal lobe epilepsy, wherein a brief period of status epilepticus (SE) triggers development of spontaneous recurrent seizures that appear after a latency of 2-3 weeks. Here we investigate changes in expression of A-type voltage-gated potassium (Kv) channels, which control neuronal excitability and regulate action potential propagation and neurotransmitter release, in the pilocarpine model of epilepsy. Using immunohistochemistry, we examined the expression of component subunits of somatodendritic (Kv4.2, Kv4.3, KChIPl and KChIP2) and axonal (Kv1.4) A-type Kv channels in hippocampi of pilocarpine-treated rats that entered SE. We found that Kv4.2, Kv4.3 and KChIP2 staining in the molecular layer of the dentate gyrus changes from being uniformly distributed across the molecular layer to concentrated in just the outer two-thirds. We also observed a loss of KChIP1 immunoreactive interneurons, and a reduction of Kv4.2 and KChIP2 staining in stratum radiatum of CA1. These changes begin to appear 1 week after pilocarpine treatment and persist or are enhanced at 4 and 12 weeks. As such, these changes in Kv channel distribution parallel the acquisition of recurrent spontaneous seizures as observed in this model. We also found temporal changes in Kv1.4 immunoreactivity matching those in Timm's stain, being expanded in stratum lucidum of CA3 and in the inner third of the dentate molecular layer. Among pilocarpine-treated rats, changes were only observed in those that entered SE. These changes in A-type Kv channel expression may contribute to hyperexcitability of dendrites in the associated hippocampal circuits as observed in previous studies of the effects of pilocarpine-induced SE.     

Regulation of cardiac shal-related potassium channel Kv 4.3 by serum- and glucocorticoid-inducible kinase isoforms in Xenopus oocytes

The human cardiac transient outward potassium current I_to is formed by co-assembly of voltage-dependent K⁺ channel (Kv 4.3) pore-forming -subunits with differently spliced K channel interacting protein (KChIP) accessory proteins. I_to is of considerable importance for the normal course of the cardiac ventricular action potential. The present study was performed to determine whether isoforms of the serum- and glucocorticoid-inducible kinase (SGK) family influence Kv 4.3/KChIP2b channel activity in the Xenopus laevis heterologous expression system. Co-expression of SGK1, but not of SGK2 or SGK3, increased Kv 4.3/KChIP2b channel currents. The up-regulation of the current was not due to changes in the activation curve or changes of channel inactivation. The currents in oocytes expressing Kv 4.3 alone were smaller than those in Kv 4.3/KChIP2b expressing oocytes, but were still stimulated by SGK1. The effect of wild-type SGK1 was mimicked by constitutively active SGK1 (SGK1 S422D) but not by an inactive mutant (SGK1 K127N). The current amplitude increase mediated by SGK1 was not dependent on NEDD4.2 or RAB5, nor did it reflect increased cell surface expression. In conclusion, SGK1 stimulates Kv 4.3 potassium channels expressed in Xenopus oocytes by a novel mechanism distinct from the known NEDD4.2-dependent pathway.     

Kv2.1 voltage-gated potassium channels in developmental perspective

Kv2.1 voltage-gated potassium channels consist of two types of α-subunits: (a) electrically-active Kcnb1 α-subunits and (b) silent or modulatory α-subunits plus β-subunits that, similar to silent α-subunits, also regulate electrically-active subunits. Voltage-gated potassium channels were traditionally viewed, mainly by electrophysiologists, as regulators of the electrical activity of the plasma membrane in excitable cells, a role that is performed by transmembrane protein domains of α-subunits that form the electric pore. Genetic studies revealed a role for this region of α-subunits of voltage-gated potassium channels in human neurodevelopmental disorders, such as epileptic encephalopathy. The N- and C-terminal domains of α-subunits interact to form the cytoplasmic subunit of heterotetrameric potassium channels that regulate electric pores. Subsequent animal studies revealed the developmental functions of Kcnb1-containing voltage-gated potassium channels and illustrated their role during brain development and reproduction. These functions of potassium channels are discussed in this review in the context of regulatory interactions between electrically-active and regulatory subunits.     

Differential expression of Kv3.1b and Kv3.2 potassium channel subunits in interneurons of the basolateral amygdala

The expression of Kv3.1 and Kv3.2 voltage-gated potassium channel subunits appears to be critical for high-frequency firing of many neuronal populations. In the cortex these subunits are mainly associated with fast-firing GABAergic interneurons containing parvalbumin or somatostatin. Since the basolateral nuclear complex of the amygdala contains similar interneurons, it is of interest to determine if these potassium channel subunits are expressed in these same interneuronal subpopulations. To investigate this issue, peroxidase and dual-labeling fluorescence immunohistochemistry combined with confocal laser scanning microscopy was used to determine which interneuronal subpopulations in the basolateral nuclear complex of the rat amygdala express Kv3.1b and Kv3.2 subunits. Antibodies to parvalbumin, somatostatin, calretinin, and cholecystokinin were used to label separate subsets of basolateral amygdalar interneurons. Examination of immunoperoxidase preparations suggested that the expression of both channels was restricted to nonpyramidal interneurons in the basolateral amygdala. Somata and proximal dendrites were intensely-stained, and axon terminals arising from presumptive basket cells and chandelier cells were lightly stained. Immunofluorescence observations revealed that parvalbumin+ neurons were the main interneuronal subpopulation expressing the Kv3.1b potassium channel subunit in the basolateral amygdala. More than 92-96% of parvalbumin+ neurons were Kv3.1b+, depending on the nucleus. These parvalbumin+/Kv3.1b+ double-labeled cells constituted 90-99% of all Kv3.1b+ neurons. Parvalbumin+ neurons were also the main interneuronal subpopulation expressing the Kv3.2 potassium channel subunit. More than 67-78% of parvalbumin+ neurons were Kv3.2+, depending on the nucleus. However, these parvalbumin+/Kv3.2+ double-labeled cells constituted only 71-81% of all Kv3.2+ neurons. Most of the remaining neurons with significant levels of the Kv3.2 subunit were somatostatin+ interneurons. These Kv3.2-containing somatostatin+ interneurons constituted 27-50% of the somatostatin+ population, depending on the nucleus in question. These data suggest that both fast-firing and burst-firing parvalbumin+ interneurons in the basolateral amygdala express the Kv3.1b subunit. The significance of Kv3.2 expression in some parvalbumin+ and somatostatin+ interneurons remains to be determined.     

Altered expression of voltage-gated potassium channel 4.2 and voltage-gated potassium channel 4-interacting protein, and changes in intracellular calcium levels following lithium-pilocarpine-induced status epilepticus

The A-type voltage-gated potassium channels (Kv4) have been proved to play a major role as modulators of somatodendritic excitability. Recent studies indicate that neuronal hyperactivity in epilepsy is associated with changes in Kv4. However, the precise regulation of Kv4 in the development of epilepsy and its underlying mechanism remain unclear. In this study, we investigated whether the expression of the Kv4.2 channel and of its major modulator, voltage-dependent potassium channel-interacting protein (KChIP1), is altered following lithium-pilocarpine induced status epilepticus (SE) and the chronic-epilepsy phase in the rat model. We found that Kv4.2 and KChIP1 expression was transiently up-regulated following SE, whereas it was down-regulated during the chronic phase: this was most prominent in the CA1 and CA3 regions. The time-course analysis of the protein expression level showed that the peak Kv4.2 up-regulation was between 6 and 24 h after SE, whereas KChIP1 expression was increased earlier and for a shorter period. The temporospatial changes in Kv4.2 were very similar to those of its major modulator KChIP1. We compared the difference in 4-aminopyridine (4-AP)-induced intracellular calcium ([Ca(2+)]i) elevation between model and control brain slices. The results showed that the [Ca(2+)]i elevation induced by the Kv4 channel blocker 4-AP was aggravated and prolonged in the model slice after SE. The functional relevance of these changes in Ca(2+) homeostasis and Kv4.2 and KChIP1 expression may be associated with intrinsic neuronal excitability regulation and epileptogenesis.     

Structural basis for modulation of Kv4 K+ channels by auxiliary KChIP subunits

KChIPs coassemble with pore-forming Kv4 alpha subunits to form a native complex in the brain and heart and regulate the expression and gating properties of Kv4 K(+) channels, but the mechanisms underlying these processes are unknown. Here we report a co-crystal structure of the complex of human Kv4.3 N-terminus and KChIP1 at a 3.2-A resolution. The structure reveals a unique clamping action of the complex, in which a single KChIP1 molecule, as a monomer, laterally clamps two neighboring Kv4.3 N-termini in a 4:4 manner, forming an octamer. The proximal N-terminal peptide of Kv4.3 is sequestered by its binding to an elongated groove on the surface of KChIP1, which is indispensable for the modulation of Kv4.3 by KChIP1, and the same KChIP1 molecule binds to an adjacent T1 domain to stabilize the tetrameric Kv4.3 channels. Taken together with biochemical and functional data, our findings provide a structural basis for the modulation of Kv4 by KChIPs.     

Kv4钾通道及其相互作用蛋白KChIP2与心律失常

心肌细胞动作电位复极化异常与心律失常的发生有密切关系。Ito电流是参与心肌细胞动作电位复极化的重要离子流。Kv4.2 或Kv4.3是形成Ito通道孔洞的亚基，而Kv4钾通道相互作用蛋白KChIP2则协助在胞质合成的Kv4.2 或Kv4.3向细胞膜转运。Kv4钾通道及KChIP2在心肌细胞的表达、分布和功能的变化对心肌细胞Ito电流有重要影响。     

Postnatal development of A-type and Kv1- and Kv2-mediated potassium channel currents in neocortical pyramidal neurons

Potassium channels regulate numerous aspects of neuronal excitability, and several voltage-gated K(+) channel subunits have been identified in pyramidal neurons of rat neocortex. Previous studies have either considered the development of outward current as a whole or divided currents into transient, A-type and persistent, delayed rectifier components but did not differentiate between current components defined by α-subunit type. To facilitate comparisons of studies reporting K(+) currents from animals of different ages and to understand the functional roles of specific current components, we characterized the postnatal development of identified Kv channel-mediated currents in pyramidal neurons from layers II/III from rat somatosensory cortex. Both the persistent/slowly inactivating and transient components of the total K(+) current increased in density with postnatal age. We used specific pharmacological agents to test the relative contributions of putative Kv1- and Kv2-mediated currents (100 nM α-dendrotoxin and 600 nM stromatoxin, respectively). A combination of voltage protocol, pharmacology, and curve fitting was used to isolate the rapidly inactivating A-type current. We found that the density of all identified current components increased with postnatal age, approaching a plateau at 3-5 wk. We found no significant changes in the relative proportions or kinetics of any component between postnatal weeks 1 and 5, except that the activation time constant for A-type current was longer at 1 wk. The putative Kv2-mediated component was the largest at all ages. Immunocytochemistry indicated that protein expression for Kv4.2, Kv4.3, Kv1.4, and Kv2.1 increased between 1 wk and 4-5 wk of age.     

Functional interaction between KChIP1 and GFP-fused Kv4.3L co-expressed in HEK293 cells

The trafficking and electrophysiological characteristics of Kv4 subfamily are regulated by K+-channel-interacting proteins (KChIPs), which bind to the N-terminus of Kv4. We examined in HEK293 expression system whether the fusion of a green fluorescence protein (GFP) with Kv4.3L at the N-terminus would affect the functional interaction of KChIP1 with Kv4.3L. GFP-fused Kv4.3L showed A-type K+ current (I(A)) with significantly slower recovery from inactivation (tau=218 and 496 ms) and much lower density than those of original Kv4.3L expressed in HEK293 cells. The co-expression of KChIP1 with Kv4.3L strikingly increased the density of I(A) and hastened the recovery from inactivation (tau=133 ms). Surprisingly, co-expression of KChIP1 with GFP-fused Kv4.3L markedly enhanced the current density and hastened the recovery (tau=135 ms), just as the co-expression of KChIP1 with Kv4.3L did. In conclusion, the fusion of GFP to the N-terminus of Kv4.3L per se changed the channel kinetics but did not affect the functional interaction of KChIP1 with Kv4.3L at all. The trafficking of Kv4.3L by KChIP1 to the cell membrane was visualized with GFP fusion to the N-terminus without any significant modification of changes in channel kinetics and density.     

Contribution of N- and C-terminal channel domains to Kv channel interacting proteins in a mammalian cell line

Association of Shal gene-related voltage-gated potassium (Kv4) channels with cytoplasmic Kv channel interacting proteins (KChIPs) influences inactivation gating and surface expression. We investigated both functional and biochemical consequences of mutations in cytoplasmic N and C-terminal Kv4.2 domains to characterize structural determinants for KChIP interaction. We performed a lysine-scanning mutagenesis within the proximal 40 amino acid portion and a structure-based mutagenesis in the tetramerization 1 (T1) domain of Kv4.2. In addition, the cytoplasmic Kv4.2 C-terminus was truncated at various positions. Wild-type and mutant Kv4.2 channels were coexpressed with KChIP2 isoforms in mammalian cell lines. The KChIP2-induced modulation of Kv4.2 currents was studied with whole-cell patch clamp and the binding of KChIP2 isoforms to Kv4.2 channels with coimmunoprecipitation experiments. Our results define one major interaction site for KChIPs, including amino acids in the proximal N-terminus between residues 11 and 23, where binding and functional modulation are essentially equivalent. A further interaction site includes residues in the T1 domain. Notably, C-terminal deletions also had marked effects on KChIP2-dependent gating modulation and KChIP2 binding, revealing a previously unknown involvement of domains within the cytoplasmic Kv4.2 C-terminus in KChIP interaction. Less coincidence of binding and functional modulation indicates a more loose 'anchoring' at T1- and C-terminal interaction sites. Our results refine and extend previously proposed structural models for Kv4.2/KChIP complex formation.     

Kv1 potassium channel complexes in vivo require Kvbeta2 subunits in dorsal spinal neurons

Whereas Kvβ2 subunits modulate potassium current properties carried by Kv1 channel complexes in heterologous systems, little is known about the contributions of Kvβ2 subunits to native potassium channel function. Using antisense approaches and in situ recordings from Xenopus embryo spinal cord neurons, we tested the in vivo roles of Kvβ2 subunits in modulation of voltage-dependent potassium current (I_Kv). We focused on 1) two different populations of dorsal spinal neurons that express both Kvβ2 and Kv1 -subunit genes and 2) the 24- and 48-h developmental period, during which I_Kv undergoes developmental regulation. At both 24 and 48 h, antisense methods produced efficient knock-down of both Kvβ2 protein and I_Kv. At both times, dominant negative suppression of Kv1 channels also eliminated I_Kv, indicating that Kv1 channels require Kvβ2 subunits to function in dorsal spinal neurons. Even though Kv1 channels determined the I_Kv values of both dorsal neuron types, comparisons of their I_Kv properties revealed important differences at both developmental stages. The latter results support the notion that different Kv1 -subunits and/or posttranslational modifications underlie the I_Kv values of the two dorsal neuron types. Overall, the results demonstrate that Kvβ2 subunits function in vivo as obligatory subunits of Kv1 channels in at least two neuron types and two different developmental stages.     

Impaired glycosylation blocks DPP10 cell surface expression and alters the electrophysiology of I to channel complex

DPP10 is a transmembrane glycosylated protein belonging to the family of dipeptidyl aminopeptidase-like proteins (DPPLs). DPPLs are auxiliary subunits involved in the regulation of voltage-gated Kv4 channels, key determinants of cardiac and neuronal excitability. Although it is known that DPPLs are needed to generate native-like currents in heterologous expression systems, the molecular basis of this involvement are still poorly defined. In this study, we investigated the functional relevance of DPP10 glycosylation in modulating Kv4.3 channel activities. Using transfected Chinese hamster ovary (CHO) cells to reconstitute Kv4 complex, we show that the pharmacological inhibition of DPP10 glycosylation by tunicamycin and neuraminidase affects transient outward potassium current (I _to) kinetics. Tunicamycin completely blocked DPP10 glycosylation and reduced DPP10 cell surface expression. The accelerating effects of DPP10 on Kv4.3 current kinetics, i.e. on inactivation and recovery from inactivation, were abolished. Neuraminidase produced different effects on current kinetics than tunicamycin, i.e., shifted the voltage dependence to more negative potentials. The effects of tunicamycin on the native I _to currents of human atrial myocytes expressing DPP10 were similar to those of the KV4.3/KChIP2/DPP10 complex in CHO cells. Our results suggest that N-linked glycosylation of DPP10 plays an important role in modulating Kv4 channel activities.     

Bisoprolol reverses down-regulation of potassium channel proteins in ventricular tissues of rabbits with heart failure

Remodeling of ion channels is an important mechanism of arrhythmia induced by heart failure (HF).We investigated the expression of potassium channel encoding genes in the ventricles of rabbit established by volumeoverload operation followed with pressure-overload.The reversible effect of these changes with bisoprolol was also evaluated.The HF group exhibited left ventricular enlargement,systolic dysfunction,prolongation of corrected QT interval (QTc),and increased plasma brain natriuretic peptide levels in the HF rabbits.Several potassium channel subunit encoding genes were consistently down-regulated in the HF rabbits.After bisoprolol treatment,heart function was improved significantly and QTc was shortened.Additionally,the mRNA expression of potassium channel subunit genes could be partially reversed.The down-regulated expression of potassium channel subunits Kv4.3,Kv1.4,KvLQT1,minK and Kir 2.1 may contribute to the prolongation of action potential duration in the heart of rabbits induced by volume combined with pressure overload HF.Bisoprolol could partially reverse these down-regulations and improve heart function.     

Seizures and reduced life span in mice lacking the potassium channel subunit Kv1.2, but hypoexcitability and enlarged Kv1 currents in auditory neurons

Genes Kcna1 and Kcna2 code for the voltage-dependent potassium channel subunits Kv1.1 and Kv1.2, which are coexpressed in large axons and commonly present within the same tetramers. Both contribute to the low-voltage-activated potassium current I Kv1, which powerfully limits excitability and facilitates temporally precise transmission of information, e.g., in auditory neurons of the medial nucleus of the trapezoid body (MNTB). Kcna1-null mice lacking Kv1.1 exhibited seizure susceptibility and hyperexcitability in axons and MNTB neurons, which also had reduced I Kv1. To explore whether a lack of Kv1.2 would cause a similar phenotype, we created and characterized Kcna2-null mice (-/-). The -/- mice exhibited increased seizure susceptibility compared with their +/+ and +/- littermates, as early as P14. The mRNA for Kv1.1 and Kv1.2 increased strongly in +/+ brain stems between P7 and P14, suggesting the increasing importance of these subunits for limiting excitability. Surprisingly, MNTB neurons in brain stem slices from -/- and +/- mice were hypoexcitable despite their Kcna2 deficit, and voltage-clamped -/- MNTB neurons had enlarged I Kv1. This contrasts strikingly with the Kcna1-null MNTB phenotype. Toxin block experiments on MNTB neurons suggested Kv1.2 was present in every +/+ Kv1 channel, about 60% of +/- Kv1 channels, and no -/- Kv1 channels. Kv1 channels lacking Kv1.2 activated at abnormally negative potentials, which may explain why MNTB neurons with larger proportions of such channels had larger I Kv1. If channel voltage dependence is determined by how many Kv1.2 subunits each contains, neurons might be able to fine-tune their excitability by adjusting the Kv1.1:Kv1.2 balance rather than altering Kv1 channel density.     

Complex expression and localization of inactivating Kv channels in cultured hippocampal astrocytes

Voltage-gated potassium channels are well established as critical for setting action potential frequency, membrane potential, and neurotransmitter release in neurons. However, their role in the "nonexcitable" glial cell type is yet to be fully understood. We used whole cell current kinetics, pharmacology, immunocytochemistry, and RT-PCR to characterize A-type current in hippocampal astrocyte cultures to better understand its function. Pharmacological analysis suggests that approximately 70, 10, and <5% of total A current is associated with Kv4, Kv3, and Kv1 channels, respectively. In addition, pharmacology and kinetics provide evidence for a significant contribution of KChIP accessory proteins to astrocytic A-channel composition. Localization of the Shaw Kv3.4 channel to astrocytic processes and the Shal Kv4.3 channel to soma suggest that these channels serve a specific function. Given this complex A-type channel expression pattern, we assessed the role of A currents in membrane voltage oscillations in response to current injections. Although TEA-sensitive delayed-rectifying currents are involved in the extent of repolarization, 4-AP-sensitive A currents serve to increase the rate. As in neurons, this effect may enable astrocytes to respond rapidly to high-frequency synaptic events. Our results indicate that hippocampal astrocytes in vitro express multiple A-type Kv channel alpha-subunits with accessory, possibly Ca(2+)-sensitive, cytoplasmic subunits that appear to be specifically localized to subcellular membrane compartments. Function of these channels remains to be determined in a physiological setting. However, this study suggests that they enable astrocytes to respond rapidly with membrane voltage oscillations to high-frequency incoming signals, possibly synchronizing astrocyte function to neuronal activity.     

Hyperexcitability and reduced low threshold potassium currents in auditory neurons of mice lacking the channel subunit Kv1.1

A low voltage-activated potassium current, I _KL, is found in auditory neuron types that have low excitability and precisely preserve the temporal pattern of activity present in their presynaptic inputs. The gene Kcna1 codes for Kv1.1 potassium channel subunits, which combine in expression systems to produce channel tetramers with properties similar to those of I _KL, including sensitivity to dendrotoxin (DTX). Kv1.1 is strongly expressed in neurons with I _KL, including auditory neurons of the medial nucleus of the trapezoid body (MNTB). We therefore decided to investigate how the absence of Kv1.1 affected channel properties and function in MNTB neurons from mice lacking Kcna1 . We used the whole cell version of the patch clamp technique to record from MNTB neurons in brainstem slices from Kcna1 -null (−/−) mice and their wild-type (+/+) and heterozygous (+/−) littermates. There was an I _KL in voltage-clamped −/− MNTB neurons, but it was about half the amplitude of the I _KL in +/+ neurons, with otherwise similar properties. Consistent with this, −/− MNTB neurons were more excitable than their +/+ counterparts; they fired more than twice as many action potentials (APs) during current steps, and the threshold current amplitude required to generate an AP was roughly halved. +/− MNTB neurons had excitability and I _KL amplitudes identical to the +/+ neurons. The I _KL remaining in −/− neurons was blocked by DTX, suggesting the underlying channels contained subunits Kv1.2 and/or Kv1.6 (also DTX-sensitive). DTX increased excitability further in the already hyperexcitable −/− MNTB neurons, suggesting that −/− I _KL limited excitability despite its reduced amplitude in the absence of Kv1.1 subunits.     

A voltage-gated potassium channel, Kv3.1b, is expressed by a subpopulation of large pyramidal neurons in layer 5 of the macaque monkey cortex

In the cerebral cortex, the voltage-gated potassium channel, Kv3.1b, a splicing variant of Kv3.1, has been associated with fast-firing interneurons. Here, we report strong expression of Kv3.1b-protein and mRNA in both Betz and Meynert pyramidal cells of the monkey, as shown by immunohistochemistry and in situ hybridization. Strong expression also occurs in large pyramidal neurons in layer 5 of several cortical areas. In addition, most of these Betz and layer 5 pyramids, and about 10% of the labeled Meynert cells weakly co-expressed the calcium binding protein parvalbumin. Electron microscopy shows that the expression of Kv3.1b is localized to the somal and proximal dendritic cytoplasmic membrane, as expected for a channel protein. These results suggest that some large pyramidal neurons may constitute a functional subpopulation, with a distinctive distribution of voltage-gated potassium channels capable of influencing their repetitive firing properties.