Na⁺‐activated K⁺ channels in small dorsal root ganglion neurones of rat

Abstract

Whole‐cell Na+‐activated K+ (KNa) channel currents and single KNa channels were studied with the patch‐clamp method in small (20‐25 μm) dorsal root ganglion (DRG) neurones in slices of rat dorsal root ganglia. The whole‐cell KNa channel current was identified as an additional K+‐selective leakage current which appeared after cell perfusion with internal solutions containing different [Na+]. The concentration for half‐maximal activation of KNa channel current was 39 mM and the Hill coefficient was 3.5. At [Na+]i above 12 mM, KNa channel current dominated the unspecific leakage current. The ratio of maximum KNa channel current to unspecific leakage current was 45. KNa channel current was not activated by internal Li+. It was suppressed by external 20 mM Cs+ but not by 10 mM tetraethylammonium. Single KNa channels with a conductance of 142 pS in 155 mM external K+ (K+o)‐85 mM internal K+ (K+i) solutions were observed at a high density of about 2 channels μm−2. In two‐electrode experiments, a direct correlation was seen between development of whole‐cell KNa channel current and activation of single KNa channels during perfusion of the neurone with Na+‐containing internal solution. Under current‐clamp conditions, KNa channels did not contribute to the action potential. However, internal perfusion of the neurone with Na+ shifted the resting potential towards the equilibrium potential for K+ (EK). Varying external [K+] indicated that in neurones perfused with Na+‐containing internal solution the resting potential followed the EK values predicted by the Nernst equation over a broader voltage range than in neurones perfused with Na+‐free solution. It is concluded that the function of KNa channels has no links to firing behaviour but that the channels could be involved in setting or stabilizing the resting potential in small DRG neurones.

NAD+Activates KNaChannels in Dorsal Root Ganglion Neurons

“…• K Na Channels Are Modulated by NAD ϩ nohistochemical data and is similar to what has been reported earlier (Bischoff et al, 1998;Gao et al, 2008). The K Na channel EC 50 s for Na ϩ was determined to be 53 mM (n ϭ 6) and 55 mM (n ϭ 6) in small neurons (Fig.…”

“…Previous work has documented that K Na channels can be recorded in small-and medium-sized DRG neurons (Bischoff et al, 1998;Gao et al, 2008), and we have now demonstrated that K Na channels are also present in large, proprioceptive DRG neurons. The Na ϩ -doseresponse relationship for K Na channels for both small and large DRG neurons was determined to be similar.…”

“…Among DRG neurons, K Na channels have only been studied in rat neonatal small DRG neurons (Bischoff et al, 1998) or in adult medium-sized DRG neurons (Gao et al, 2008). In this study, we show that Slack K Na channels are ubiquitously expressed in adult rat DRG neurons.…”

“…In some neurons, these channels have been suggested to control the resting membrane potential (Haimann et al, 1992;Koh et al, 1994;Bischoff et al, 1998). Recent evidence indicates that in adult medium-sized dorsal root ganglion (DRG) neurons, a single Na ϩ -dependent action potential can elicit a K Na current, and K Na channels were suggested to regulate the depolarizing after potential (DAP) (Gao et al, 2008).…”

Roles of Tetrodotoxin (TTX)-Sensitive Na+Current, TTX-Resistant Na+Current, and Ca2+Current in the Action Potentials of Nociceptive Sensory Neurons

“…In addition, the calcium current most likely activates a counterbalancing calcium-activated potassium current during the action potential shoulder. In contrast, Na entry through TTX-R sodium channels probably does not activate a potassium current; although Na-activated potassium currents are known to exist in small DRG neurons, they do not appear to be activated during single action potentials (Bischoff et al, 1998).…”