Modulation of Kv3.1b Potassium Channel Phosphorylation in Auditory Neurons by Conventional and Novel Protein Kinase C Isozymes

Abstract

In fast-spiking neurons such as those in the medial nucleus of the trapezoid body (MNTB) in the auditory brainstem, Kv3.1 potassium channels are required for high frequency firing. The Kv3.1b splice variant of this channel predominates in the mature nervous system and is a substrate for phosphorylation by protein kinase C (PKC) at Ser-503. In resting neurons, basal phosphorylation at this site decreases Kv3.1 current, reducing neuronal ability to follow high frequency stimulation. We used a phospho-specific antibody to determine which PKC isozymes control serine 503 phosphorylation in Kv3.1b-tranfected cells and in auditory neurons in brainstem slices. By using isozyme-specific inhibitors, we found that the novel PKC-␦ isozyme, together with the novel PKC-⑀ and conventional PKCs, contributed to the basal phosphorylation of Kv3.1b in MNTB neurons. In contrast, only PKC-⑀ and conventional PKCs mediate increases in phosphorylation produced by pharmacological activation of PKC in MNTB neurons or by metabotropic glutamate receptor activation in Kv3.1/mGluR1-cotransfected cells. We also measured the time course of dephosphorylation and recovery of basal phosphorylation of Kv3.1b following brief high frequency electrical stimulation of the trapezoid body, and we determined that the recovery process is mediated by both novel PKC-␦ and PKC-⑀ isozymes and by conventional PKCs. The association between Kv3.1b and PKC isozymes was confirmed by reciprocal coimmunoprecipitation of Kv3.1b with multiple PKC isozymes. Our results suggest that the Kv3.1b channel is regulated by both conventional and novel PKC isozymes and that novel PKC-␦ contributes specifically to the maintenance of basal phosphorylation in auditory neurons.There is a good correlation between the ability of neurons to discharge at high rates and the expression of Kv3 family potassium channels, particularly the Kv3.1 channel (1-5). Neurons that express Kv3.1 at high levels include those in the medial nucleus of the trapezoid body (MNTB) 2 within the auditory brainstem (6 -8). The MNTB is key element of neural pathways that detect differences in the level or timing of interaural stimuli to compute sound localization. MNTB neurons are able to fire at frequencies of hundreds of Hz (9, 10) and to lock their action potentials precisely to the phase of auditory stimuli at frequencies of up to 2-4 kHz or to rapid fluctuations in the amplitude of high frequency sounds (11). One important physiological specialization enabling MNTB neurons to fire at such high frequencies is the high level of expression of Kv3.1 potassium channels. Genetic knock-out of the Kv3.1 gene, as well as pharmacological and computer modeling studies, confirms that a high threshold component of potassium current in MNTB neurons is carried by Kv3.1 channels and that its elimination impairs the neuronal response to high frequency stimulation (12)(13)(14). Nevertheless, high levels of Kv3.1b current degrade the accuracy of action potential timing at lower frequencies of firing (14 -16).Two isoforms of ...

Intrinsic plasticity induced by group II metabotropic glutamate receptors via enhancement of high-threshold KV currents in sound localizing neurons

“…One way PLC may influence K V currents is via protein kinase C (PKC) because PLC is known to modulate PKC activity via degradation of phosphatidylinositol 4,5-bisphosphate into diacyl glycerol and inositol 1,4,5-trisphosphate. Previous work on K V modulation in the mammalian sound localization circuit, as well as in many other brain regions, has shown that PKC can modulate HTK currents (Atzori et al, 2000; Sun et al, 2003), including HTK currents mediated by K V 3.1 channels (Critz et al, 1993; Liu and Kaczmarek, 1998; Macica et al, 2003; Song et al, 2005; Song and Kaczmarek, 2006). To test whether PKC was involved, slices were pre-incubated for at least 30 mins in a cell permeable PKC blocker Go6983 (20 nM), which non-selectively blocks all PKC subunits with the exception of PKC μ (Gschwendt et al, 1996; Peterman et al, 2004).…”

“…Augustine and Bezanilla, 1990; Atzori et al, 2000; Strumbos et al, 2010). Much of the literature concerning phosphorylation-induced changes in K V 3 currents has shown that PKC is intimately involved (Liu and Kaczmarek, 1998; Macica et al, 2003; Sun et al, 2003; Song et al, 2005; Song and Kaczmarek, 2006). However, exactly how activation of mGluR II leads to activation of the G βγ complex, which changes PKC activity via PLC, and ultimately causes an enhancement of HTK currents in NL neurons, awaits more investigation.…”

Metabotropic glutamate receptors in auditory processing

“…1C). Besides mediating such retro-suppression of neurotransmission, activation of group I mGluRs also increases phosphorylation of K v 3.1b (Song and Kaczmarek, 2006), which is a critical factor defining the ability of MNTB neurons to follow high frequency inputs (reviewed in Johnston et al, 2010). Physiological function of group II mGluRs in MNTB is not known.…”

Minimal sex differences in gene expression in the rat superior olivary complex

“…To this end, we compared the gene expression profile of the rat SOC in P16 males and females. This juvenile age is often used in functional SOC studies, as most properties resemble the mature situation (Ehrlich et al, 1999;Srinivasan et al, 2004;Klug and Trussell, 2006;Song and Kaczmarek, 2006;Smith et al, 2000). To validate our approach, we also analyzed the adult pituitary gland, which plays a central role in sexual development and displays anatomical (MacMaster et al, 2007) and transcriptional (Nishida et al, 2005;Zhan and Desiderio, 2003) sexual dimorphisms.…”