Article

Protein Kinase C Modulates Inactivation of Kv3.3 Channels

Department of Pharmacology, Yale School of Medicine, New Haven, Connecticut 06520, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 07/2008; 283(32):22283-94. DOI: 10.1074/jbc.M801663200
Source: PubMed

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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    • "However, incorporation of a single subunit containing the N-terminal extension is sufficient to confer inactivation on the channel, although it occurs at a slower rate than in channels composed of four inactivating subunits (MacKinnon et al. 1993). We generated a non-inactivating form of Kv3.3, Kv3.3-IR (inactivation removed), by deleting the N-terminal extension and then co-expressed it with R420H in the normal, inactivating background at ratios of 1:1 and 1:4 (IR:R420H) (Fig. 1C) (Desai et al. 2008). For comparison, wild type Kv3.3 and Kv3.3-IR channels were expressed separately. "
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    • "We have observed variability in the rate of Kv3.3 inactivation in oocytes, perhaps due to differences in the basal level of protein kinase C (PKC) activity. Phosphorylation of Kv3.3 by PKC slows inactivation (Desai, et al., 2008). "
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