Few cultured rat primary sensory neurons express a tolbutamide-sensitive K+ current

The response of dorsal root ganglion (DRG) neurons to metabolic inhibition is known to involve calcium-activated K⁺ channels; in most neuronal types ATP-sensitive K⁺ channels (K_ATP) also contribute, but this is not yet established in the DRG. We have investigated the presence of a K_ATP current using whole-cell recordings from rat DRG neurons, classifying the neurons functionally by their "current signature" (Petruska et al, J Neurophysiol 84: 2365–2379, 2000). We clearly identified a K_ATP current in only 1 out of 62 neurons, probably a nociceptor. The current was activated by cyanide (2 mM NaCN) and was sensitive to 100 μM tolbutamide; the relation between reversal potential and external K⁺ concentration indicated it was a K⁺ current. In a further two neurons, cyanide activated a K⁺ current that was only partially blocked by tolbutamide, which may also be an atypical K_ATP current. We conclude that K_ATP channels are expressed in normal DRG, but in very few neurons and only in nociceptors.