NAD⁺Activates K_NaChannels in Dorsal Root Ganglion Neurons

Abstract

Although sodium-activated potassium channels (K Na ) have been suggested to shape various firing patterns in neurons, including action potential repolarization, their requirement for high concentrations of Na ϩ to gate conflicts with this view. We characterized K Na channels in adult rat dorsal root ganglion (DRG) neurons. Using immunohistochemistry, we found ubiquitous expression of the Slack K Na channel subunit in small-, medium-, and large-diameter DRG neurons. Basal K Na channel activity could be recorded from cell-attached patches of acutely dissociated neurons bathed in physiological saline, and yet in excised inside-out membrane patches, the Na ϩ EC 50 for K Na channels was typically high, ϳ50 mM. In some cases, however, K Na channel activity remained considerable after initial patch excision but decreased rapidly over time. Channel activity was restored in patches with high Na ϩ . The channel rundown after initial excision suggested that modulation of channels might be occurring through a diffusible cytoplasmic factor. Sequence analysis indicated that the Slack channel contains a putative nicotinamide adenine dinucleotide (NAD ϩ )-binding site; accordingly, we examined the modulation of native K Na and Slack channels by NAD ϩ . In inside-out-excised neuronal patch recordings, we found a decrease in the Na ϩ EC 50 for K Na channels from ϳ50 to ϳ20 mM when NAD ϩ was included in the perfusate. NAD ϩ also potentiated recombinant Slack channel activity. NAD ϩ modulation may allow K Na channels to operate under physiologically relevant levels of intracellular Na ϩ and hence provides an explanation as to how K Na channel can control normal neuronal excitability.

PKA-Induced Internalization of Slack KNaChannels Produces Dorsal Root Ganglion Neuron Hyperexcitability

“…Like their adult counterparts (Tamsett et al, 2009), embryonic cultured DRG neurons abundantly express the Slack subunit (Fig. 1 A).…”

“…K Na channels are abundantly expressed in the cell bodies and axons of nociceptive DRG neurons (Bischoff et al, 1998;Tamsett et al, 2009), and suggested to regulate DRG neuronal resting membrane potential (RMP) (Bischoff et al, 1998). In neuronal simulations, K Na channels caused firing accommodation Brown et al, 2008).…”

The Antipsychotic Drug Loxapine Is an Opener of the Sodium-Activated Potassium Channel Slack (Slo2.2)

“…Mutational analyses indicated that Na ϩ binding and gating occur in RCK domain 2 (Zhang et al, 2010). Slack channels are widely expressed throughout the rat central nervous system, including the substantia nigra (SN), but also are abundantly expressed in peripheral dorsal root ganglion (DRG) neurons (Bhattacharjee et al, 2002;Tamsett et al, 2009). Because Slack channels are activated by both voltage and cytosolic factors such as intracellular Na ϩ and Cl Ϫ , they are ideal effectors of negative feedback during neuronal excitation.…”

KCNT1 gain-of-function mutations linked to human epilepsy are modulated by quinidine

“…The channels expression pattern and its potential to contribute to elevated firing rates are consistent with a role in the pathogenesis of epilepsy. In the last decade research has also shown that these channels have additional modulatory functions, which are regulated by a number of signaling pathways [5][6] . The majority of the recently identified mutations [7][8][9][10] are situated in the c-terminus of the alpha subunit of KCNT1, where modulatory regions, such as the NAD + binding domain [5] and several putative consensus sites for protein kinase C (PKC) [6] are located.…”

“…In the last decade research has also shown that these channels have additional modulatory functions, which are regulated by a number of signaling pathways [5][6] . The majority of the recently identified mutations [7][8][9][10] are situated in the c-terminus of the alpha subunit of KCNT1, where modulatory regions, such as the NAD + binding domain [5] and several putative consensus sites for protein kinase C (PKC) [6] are located. Emerging evidence indicates that subtle changes in the function of this channel have a deleterious impact on the fragile developing brain [7][8][9][10] .…”