Protein kinase C modulates inactivation of Kv3.3 channels.
ABSTRACT Modulation of some Kv3 family potassium channels by protein kinase C (PKC) regulates their amplitude and kinetics and adjusts firing patterns of auditory neurons in response to stimulation. Nevertheless, little is known about the modulation of Kv3.3, a channel that is widely expressed throughout the nervous system and is the dominant Kv3 family member in auditory brainstem. We have cloned the cDNA for the Kv3.3 channel from mouse brain and have expressed it in a mammalian cell line and in Xenopus oocytes to characterize its biophysical properties and modulation by PKC. Kv3.3 currents activate at positive voltages and undergo inactivation with time constants of 150-250 ms. Activators of PKC increased current amplitude and removed inactivation of Kv3.3 currents, and a specific PKC pseudosubstrate inhibitor peptide prevented the effects of the activators. Elimination of the first 78 amino acids of the N terminus of Kv3.3 produced noninactivating currents suggesting that PKC modulates N-type inactivation, potentially by phosphorylation of sites in this region. To identify potential phosphorylation sites, we investigated the response of channels in which serines in this N-terminal domain were subjected to mutagenesis. Our results suggest that serines at positions 3 and 9 are potential PKC phosphorylation sites. Computer simulations of model neurons suggest that phosphorylation of Kv3.3 by PKC may allow neurons to maintain action potential height during stimulation at high frequencies, and may therefore contribute to stimulus-induced changes in the intrinsic excitability of neurons such as those of the auditory brainstem.
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ABSTRACT: Within auditory pathways, the intrinsic electrical properties of neurons, and in particular their complement of potassium channels, play a key role in shaping the timing and pattern of action potentials produced by sound stimuli. The Kv9.1 gene encodes a potassium channel alpha subunit that is expressed in a variety of neurons, including those of the inferior colliculus. When cRNA encoding this subunit is injected into Xenopus oocytes, no functional channels are expressed. When, however, Kv9.1 is co-expressed with certain other alpha potassium channel subunits, it changes the characteristics of the currents produced by these functional channel proteins. We have found that Kv9.1 isolated from a rat brain cDNA library alters the kinetics and the voltage-dependence of activation and inactivation of Kv2.1, a channel subunit that generates slowly inactivating delayed rectifier potassium currents. The rate of activation of Kv2.1 is slowed by co-expression with Kv9.1. With Kv2.1 alone, the amplitude of evoked currents increases monotonically with increasing command potentials. In contrast, when Kv2.1 is co-expressed with Kv9.1, the amplitude of currents increases with increasing depolarization up to potentials of only approximately +60 mV, after which increasing depolarization results in a decrease in current amplitude. Currents produced by Kv2. 1 alone and by Kv2.1/Kv9.1 are both sensitive to the potassium channel blocker tetraethyl ammonium ions (TEA), but higher concentrations of TEA (20 mM) eliminate the biphasic voltage-dependence of the Kv2.1/Kv9.1 currents. Co-expression with Kv9.1 also produces an apparent negative shift in the voltage-dependence of inactivation and activation. Computer simulations of model neurons suggest that co-expression of Kv9.1 with Kv2.1 may have different effects in neurons depending on whether their firing pattern is limited by the inactivation of inward currents. In excitable cells in which the inward currents do not inactivate, co-expression with Kv9.1 could produce an inhibition of firing during sustained depolarization. In contrast, in model neurons with rapidly inactivating inward current, the change in the voltage-dependence of activation produced by Kv9.1 may allow the cells to follow high frequency stimulation more effectively.Hearing Research 10/2000; 147(1-2):21-30. · 2.54 Impact Factor
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ABSTRACT: The Kv3.1 channel subunit, when expressed heterologously, gives rise to a high-threshold noninactivating potassium current. Experiments with auditory neurons have suggested that the presence of this channel subunit enables them to fire action potentials at high frequencies. We have found that the expression levels of Kv3.1 transcripts increase in inferior colliculus neurons before the onset of hearing and then remain relatively constant. Because spontaneous neuronal activity plays an important role in modulating neuronal excitability during development, we examined the effects of depolarization with an elevated concentration of external potassium ions on the expression of Kv3.1 channel subunits in immature inferior colliculus neurons. Elevated potassium produced a marked increase in Kv3.1 mRNA levels and in the amplitude of a high-threshold, noninactivating current before the onset of hearing. This increase was prevented by the presence of a calcium channel blocker, indicating that calcium influx mediated the depolarization-induced increase in this current. In contrast, treatment with an elevated external potassium concentration caused only a moderate increase in the peak amplitude of a lower-threshold inactivating current. The repolarization of action potentials in the high-potassium-treated cells was more rapid and complete than in the control cells. Computer simulations confirmed that this change could be explained by a change in Kv3.1-like current of the same magnitude as recorded in voltage-clamp experiments. Thus, depolarization and calcium influx may alter the excitability of immature inferior colliculus neurons by selectively increasing the levels of a Kv3. 1-like potassium current.Journal of Neuroscience 12/1998; 18(21):8758-69. · 6.91 Impact Factor
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ABSTRACT: The firing patterns of neurons in central auditory pathways encode specific features of sound stimuli, such as frequency, intensity and localization in space. The generation of the appropriate pattern depends, to a major extent, on the properties of the voltage-dependent potassium channels in these neurons. The mammalian auditory pathways that compute the direction of a sound source are located in the brainstem and include the connection from bushy cells in the anteroventral cochlear nucleus (AVCN) to the principal neurons of the medial nucleus of the trapezoid body (MNTB). To preserve the fidelity of timing of action potentials that is required for sound localization, these neurons express several types of potassium channels, including the Kv3 and Kv1 families of voltage-dependent channels and the Slick and Slack sodium-dependent channels. These channels determine the pattern of action potentials and the amount of neurotransmitter released during repeated stimulation. The amplitude of currents carried by one of these channels, the Kv3.1b channel, is regulated in the short term by protein phosphorylation, and in the long term, by changes in gene expression, such that the intrinsic excitability of the neurons is constantly being regulated by the ambient auditory environment.Hearing Research 09/2005; 206(1-2):133-45. · 2.54 Impact Factor