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 microM 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.