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Neurons in the suprachiasmatic nucleus (SCN) display coordinated circadian changes in electrical activity that are critical for daily rhythms in physiology, metabolism, and behavior. SCN neurons depolarize spontaneously and fire repetitively during the day and hyperpolarize, drastically reducing firing rates, at night. To explore the hypothesis that rapidly activating and inactivating A-type (IA) voltage-gated K+ (Kv) channels, which are also active at subthreshold membrane potentIAls, are critical regulators of the excitability of SCN neurons, we examined locomotor activity and SCN firing in mice lacking Kv1.4 (Kv1.4-/-), Kv4.2 (Kv4.2-/-), or Kv4.3 (Kv4.3-/-), the pore-forming (α) subunits of IA channels. Mice lacking either Kv1.4 or Kv4.2 α subunits have markedly shorter (0.5 h) periods of locomotor activity than wild-type (WT) mice. In vitro extracellular multi-electrode recordings revealed that Kv1.4-/-and Kv4.2-/-SCN neurons display circadIAn rhythms in repetitive firing, but with shorter periods (0.5 h) than WT cells. In contrast, the periods of wheel-running activity in Kv4.3-/- mice and firing in Kv4.3-/- SCN neurons were indistinguishable from WT animals and neurons. Quantitative real-time PCR revealed that the transcripts encoding all three Kv channelα subunits, Kv1.4, Kv4.2, and Kv4.3, are expressed constitutively throughout the day and night in the SCN. Together, these results demonstrate that Kv1.4- and Kv4.2-encoded IA channels regulate the intrinsic excitability of SCN neurons during the day and night and determine the period and amplitude of circadian rhythms in SCN neuron firing and locomotor behavior. [ABSTRACT FROM AUTHOR]

The channel pore-forming α subunit Kv4.2 is a major constituent of A-type (IA) potassium currents and a key regulator of neuronal membraneexcitability. Multiple mechanisms regulate the properties, subcellular targeting, and cell-surface expression of Kv4.2-encoded channels. In the present study, shotgun proteomic analyses of immunoprecipitated mouse brain Kv4.2 channel complexes unexpectedly identified the voltage-gated Na+ channel accessory subunit Navβ1. Voltage-clamp and current-clamp recordings revealed that knockdown of Nav&ngr;1 decreases IA densities in isolated cortical neurons and that action potential waveforms are prolonged and repetitive firing is increased in Scn1b-null cortical pyramidal neurons lacking Navβ1. Biochemical and voltage-clamp experiments further demonstrated that Navβ1 interacts with and increases the stability of the heterologously expressed Kv4.2 protein, resulting in greater total and cell-surface Kv4.2 protein expression and in larger Kv4.2-encoded current densities. Together, the results presented here identify Navβ1 as a component of native neuronal Kv4.2-encoded IA channel complexes and a novel regulator of IA channel densities and neuronal excitability. [ABSTRACT FROM AUTHOR]

Abstract: Considerable evidence indicates that native neuronal voltage-gated K+ (Kv) currents reflect the functioning of macromolecular Kv channel complexes, composed of pore-forming (α)-subunits, cytosolic and transmembrane accessory subunits, together with regulatory and scaffolding proteins. The individual components of these macromolecular complexes appear to influence the stability, the trafficking, the localization and/or the biophysical properties of the channels. Recent studies suggest that Kv channel accessory subunits subserve multiple roles in the generation of native neuronal Kv channels. Additional recent findings suggest that Kv channel accessory subunits can respond to changes in intracellular Ca2+ or metabolism and thereby integrate signaling pathways to regulate Kv channel expression and properties. Although studies in heterologous cells have provided important insights into the effects of accessory subunits on Kv channel expression/properties, it has become increasingly clear that experiments in neurons are required to define the physiological roles of Kv channel accessory and associated proteins. A number of technological and experimental hurdles remain that must be overcome in the design, execution and interpretation of experiments aimed at detailing the functional roles of accessory subunits and associated proteins in the generation of native neuronal Kv channels. With the increasing association of altered Kv channel functioning with neurological disorders, the potential impact of these efforts is clear. [Copyright &y& Elsevier]

The rapidly activating and inactivating voltage-dependent outward K+ (Kv) current, IA, is widely expressed in central and peripheral neurons. IA has long been recognized to play important roles in determining neuronal firing properties and regulating neuronal excitability. Previous work demonstrated that Kv4.2 and Kv4.3-1 subunits are the primary determinants of IA in mouse cortical pyramidal neurons. Accumulating evidence indicates that native neuronal Kv4 channels function in macromolecular protein complexes that contain accessory subunits and other regulatory molecules. The K+ channel interacting proteins (KChIPs) are among the identified Kv4 channel accessory subunits and are thought to be important for the formation and functioning of neuronal Kv4 channel complexes. Molecular genetic, biochemical, and electrophysiological approaches were exploited in the experiments described here to examine directly the roles of KChIPs in the generation of functional Kv4-encoded IA channels. These combined experiments revealed that KChIP2, KChIP3, and KChIP4 are robustly expressed in adult mouse posterior (visual) cortex and that all three proteins coimmunoprecipitate with Kv4.2. In addition, in cortical pyramidal neurons from mice lacking KChIP3 (KChIP3/), mean IA densities were reduced modestly, whereas in mean IA densities in KChIP2/andWTneurons were not significantly different. Interestingly, in both KChIP3/and KChIP2/ cortices, the expression levels of the other KChIPs (KChIP2 and 4 or KChIP3 and 4, respectively) were increased. In neurons expressing constructs to mediate simultaneous RNA interference-induced reductions in the expression of KChIP2, 3, and 4, IA densities were markedly reduced and Kv current remodeling was evident. [ABSTRACT FROM AUTHOR]

The rapidly activating and inactivating voltage-gated K+ (Kv) current, IA, is broadly expressed in neurons and is a key regulator of action potential repolarization, repetitive firing, backpropagation (into dendrites) of action potentials, and responses to synaptic inputs. Interestingly, results from previous studies on a number of neuronal cell types, including hippocampal, cortical, and spinal neurons, suggest that macroscopic IA is composed of multiple components and that each component is likely encoded by distinct Kv channel α-subunits. The goals of the experiments presented here were to test this hypothesis and to determine the molecular identities of the Kv channel α-subunits that generate IA in cortical pyramidal neurons. Combining genetic disruption of individual Kv α-subunit genes with pharmacological approaches to block Kv currents selectively, the experiments here revealed that Kv1.4, Kv4.2, and Kv4.3 α-subunits encode distinct components of IA that together underlie the macroscopic IA in mouse (male and female) cortical pyramidal neurons. Recordings from neurons lacking both Kv4.2 and Kv4.3 (Kv4.2-/-/Kv4.3-/-) revealed that, although Kv1.4 encodes a minor component of IA, the Kv1.4-encoded current was found in all the Kv4.2-/-/Kv4.3-/-cortical pyramidal neurons examined. Of the cortical pyramidal neurons lacking both Kv4.2 and Kv1.4, 90% expressed a Kv4.3-encoded IA larger in amplitude than the Kv1.4-encoded component. The experimental findings also demonstrate that the targeted deletion of the individual Kv α-subunits encoding components of IA results in electrical remodeling that is Kv α-subunit specific. [ABSTRACT FROM AUTHOR]

Neurons in the suprachiasmatic nucleus (SCN) display coordinated circadian changes in electrical activity that are critical for daily rhythms in physiology, metabolism, and behavior. SCN neurons depolarize spontaneously and fire repetitively during the day and hyperpolarize, drastically reducing firing rates, at night. To explore the hypothesis that rapidly activating and inactivating A-type (I(A)) voltage-gated K(+) (Kv) channels, which are also active at subthreshold membrane potentials, are critical regulators of the excitability of SCN neurons, we examined locomotor activity and SCN firing in mice lacking Kv1.4 (Kv1.4(-/-)), Kv4.2 (Kv4.2(-/-)), or Kv4.3 (Kv4.3(-/-)), the pore-forming (α) subunits of I(A) channels. Mice lacking either Kv1.4 or Kv4.2 α subunits have markedly shorter (0.5 h) periods of locomotor activity than wild-type (WT) mice. In vitro extracellular multi-electrode recordings revealed that Kv1.4(-/-) and Kv4.2(-/-) SCN neurons display circadian rhythms in repetitive firing, but with shorter periods (0.5 h) than WT cells. In contrast, the periods of wheel-running activity in Kv4.3(-/-) mice and firing in Kv4.3(-/-) SCN neurons were indistinguishable from WT animals and neurons. Quantitative real-time PCR revealed that the transcripts encoding all three Kv channel α subunits, Kv1.4, Kv4.2, and Kv4.3, are expressed constitutively throughout the day and night in the SCN. Together, these results demonstrate that Kv1.4- and Kv4.2-encoded I(A) channels regulate the intrinsic excitability of SCN neurons during the day and night and determine the period and amplitude of circadian rhythms in SCN neuron firing and locomotor behavior.

The rapidly activating and inactivating voltage-dependent outward K(+) (Kv) current, I(A), is widely expressed in central and peripheral neurons. I(A) has long been recognized to play important roles in determining neuronal firing properties and regulating neuronal excitability. Previous work demonstrated that Kv4.2 and Kv4.3 α-subunits are the primary determinants of I(A) in mouse cortical pyramidal neurons. Accumulating evidence indicates that native neuronal Kv4 channels function in macromolecular protein complexes that contain accessory subunits and other regulatory molecules. The K(+) channel interacting proteins (KChIPs) are among the identified Kv4 channel accessory subunits and are thought to be important for the formation and functioning of neuronal Kv4 channel complexes. Molecular genetic, biochemical, and electrophysiological approaches were exploited in the experiments described here to examine directly the roles of KChIPs in the generation of functional Kv4-encoded I(A) channels. These combined experiments revealed that KChIP2, KChIP3, and KChIP4 are robustly expressed in adult mouse posterior (visual) cortex and that all three proteins coimmunoprecipitate with Kv4.2. In addition, in cortical pyramidal neurons from mice lacking KChIP3 (KChIP3(-/-)), mean I(A) densities were reduced modestly, whereas in mean I(A) densities in KChIP2(-/-) and WT neurons were not significantly different. Interestingly, in both KChIP3(-/-) and KChIP2(-/-) cortices, the expression levels of the other KChIPs (KChIP2 and 4 or KChIP3 and 4, respectively) were increased. In neurons expressing constructs to mediate simultaneous RNA interference-induced reductions in the expression of KChIP2, 3, and 4, I(A) densities were markedly reduced and Kv current remodeling was evident.

The rapidly activating and inactivating voltage-gated K(+) (Kv) current, I(A), is broadly expressed in neurons and is a key regulator of action potential repolarization, repetitive firing, backpropagation (into dendrites) of action potentials, and responses to synaptic inputs. Interestingly, results from previous studies on a number of neuronal cell types, including hippocampal, cortical, and spinal neurons, suggest that macroscopic I(A) is composed of multiple components and that each component is likely encoded by distinct Kv channel alpha-subunits. The goals of the experiments presented here were to test this hypothesis and to determine the molecular identities of the Kv channel alpha-subunits that generate I(A) in cortical pyramidal neurons. Combining genetic disruption of individual Kv alpha-subunit genes with pharmacological approaches to block Kv currents selectively, the experiments here revealed that Kv1.4, Kv4.2, and Kv4.3 alpha-subunits encode distinct components of I(A) that together underlie the macroscopic I(A) in mouse (male and female) cortical pyramidal neurons. Recordings from neurons lacking both Kv4.2 and Kv4.3 (Kv4.2(-/-)/Kv4.3(-/-)) revealed that, although Kv1.4 encodes a minor component of I(A), the Kv1.4-encoded current was found in all the Kv4.2(-/-)/Kv4.3(-/-) cortical pyramidal neurons examined. Of the cortical pyramidal neurons lacking both Kv4.2 and Kv1.4, 90% expressed a Kv4.3-encoded I(A) larger in amplitude than the Kv1.4-encoded component. The experimental findings also demonstrate that the targeted deletion of the individual Kv alpha-subunits encoding components of I(A) results in electrical remodeling that is Kv alpha-subunit specific.