Kv3.3 Channels at the Purkinje Cell Soma Are Necessary for Generation of the Classical Complex Spike Waveform

Abstract

Voltage-gated potassium channel subunit Kv3.3 is prominently expressed in cerebellar Purkinje cells and is known to be important for cerebellar function, as human and mouse movement disorders result from mutations in Kv3.3. To understand these behavioral deficits, it is necessary to know the role of Kv3.3 channels on the physiological responses of Purkinje cells. We studied the function of Kv3.3 channels in regulating the synaptically evoked Purkinje cell complex spike, the massive postsynaptic response to the activation of climbing fiber afferents, believed to be fundamental to cerebellar physiology. Acute slice recordings revealed that Kv3.3 channels are required for generation of the repetitive spikelets of the complex spike. We found that spikelet expression is regulated by somatic, and not by dendritic, Kv3 activity, which is consistent with dual somatic-dendritic recordings that demonstrate spikelet generation at axosomatic membranes. Simulations of Purkinje cell Na ϩ currents show that the unique electrical properties of Kv3 and resurgent Na ϩ channels are coordinated to limit accumulation of Na ϩ channel inactivation and enable rapid, repetitive firing. We additionally show that Kv3.3 knock-out mice produce altered complex spikes in vitro and in vivo, which is likely a cellular substrate of the cerebellar phenotypes observed in these mice. This characterization presents new tools to study complex spike function, cerebellar signaling, and Kv3.3-dependent human and mouse phenotypes.

The Role of Kv3-type Potassium Channels in Cerebellar Physiology and Behavior

“…The reduction in paired-pulse facilitation suggests that calcium influx is already closer to saturating the release machinery during the first pulse and that neurotransmitter release is constitutively increased. In Purkinje cells, which express Kv3.4 subunits predominantly in dendrites [45], the mere absence of Kv3.3 subunits results in a doubling of simple spike duration and fewer spikelets in complex spikes [26,50,77]. There is no change in simple spike duration in Kv3.1 single mutants in agreement with the notion that Kv3.1 is not expressed in adult Purkinje cells [50].…”

“…As expected, harmaline caused tremor in wild-type and Kv3.1 mutants [50]. Harmaline however caused little or no tremor in Kv3.3 mutants, suggesting that Kv3.1 and Kv3.3 subunits play distinct roles and that the olivocerebellar circuitry may be perturbed because of altered firing patterns of Kv3.3-deficient Purkinje cells [26,77].…”

“…4, bottom). Hence, it appears that Kv3.3 channels in Purkinje cells enable rapid spike repolarization, maintain narrow simple spikes, and facilitate high-frequency firing of spikelets within complex spikes [26,77]. Although only some and not all spikelets propagate down the axon, individual spikelets propagate however with different probabilities [31,51].…”

Precise localization of the voltage-gated potassium channel subunits Kv3.1b and Kv3.3 revealed in the molecular layer of the rat cerebellar cortex by a pre-embedding immunogold method

“…Note that active zones are devoid of silver particles (arrowheads in a-e). Scale bars 0.4 lm cerebellar cortex has been made over the past few years (Perney et al 1992;Goldman-Wohl et al 1994;Weiser et al 1994Weiser et al , 1995Sabatini and Regehr 1997;Sekirnjak et al 1997;Ozaita et al 2002;Zucker and Regehr 2002;Martina et al 2003;McKay and Turner 2004;McMahon et al 2004;Akemann and Knöpfel 2006;Joho et al 2006;Chang et al 2007;Zagha et al 2008;Hurlock et al 2008Hurlock et al , 2009). However, these previous reports localized Kv3.1 and Kv3.3 with immunoperoxidase methods that yield a diffuse immunoreaction product (Ozaita et al 2002;Chang et al 2007).…”

“…Thus, lack of Kv3.3 in Purkinje neurons results in a reduction in firing rate, broader action potentials and a slower afterhyperpolarization(McMahon et al 2004;Akemann and Knöpfel 2006). Interestingly, Kv3.3 activity at the soma of Purkinje cells is very important in the regulation of evoked complex spikes in Purkinje neurons after climbing fiber activation, which is altered in mice lacking Kv3.3(Zagha et al 2008). Furthermore, the lack of Kv3.3 alone or the absence of Kv3.3 plus one Kv3.1 allele in mice causes an ataxic phenotype that is reverted after reinsertion of Kv3.3 in Purkinje cells…”