ACTIVATION BY INTRACELLULAR ATP OF A POTASSIUM CHANNEL IN NEURONS FROM RAT BASOMEDIAL HYPOTHALAMUS

1. Cell-attached recordings from isolated glucose-sensitive hypothalam ic neurones show that on removal of extracellular glucose there is an increased action current frequency concomitant with decreased single-c hannel activity. Conversely activation of single K+ channels was obser ved when extracellular glucose was increased. Isolation of membrane pa tches into the inside-out configuration following cell-attached record ing demonstrated the presence of an ATP-activated K+ channel. 2. The A TP-activated K+ channel was characterized by a mean single-channel con ductance of 132 pS in symmetrical 140 mM KCl solutions. Single-channel open-state probability (P-0) was not calcium dependent, and the prese nce of calcium did not prevent activation of the channel by ATP. 3. Ac tivation of the channel by ATP was concentration dependent and the P-0 of the ATP-activated channel was unaffected by membrane voltage, rega rdless of the degree of activation elicited by ATP. 4. Open and closed time histograms were constructed from inside-out and cell-attached re cordings and were consistent with a single open and two closed states. Channel openings were grouped in bursts. Application of ATP, in isola ted patches, and glucose, in cell attached patches, increased the burs t duration and number of bursts per second and decreased the slow clos ed-state time constant. In neither case was there a significant change in the fast closed-state time constant nor the open-state time consta nt. 5. The non-hydrolysable ATP analogue adenylylimidodiphosphate (AMP (PNP)) and 'Mg2(+)- free' ATP produced little change in the P-0 of the ATP-activated K+ channel when applied to the intracellular surface of excised patches. These results suggest that activation of this channe l is via an enzymic mechanism. 6. ADP, GTP and GDP also activated the channel in a Mg2(+)-dependent manner. ADP and ATP activated the channe l in an additive manner and neither GTP nor GDP inhibited channel acti vity induced by ATP. 7. It is concluded that the ATP-activated K+ chan nel observed in isolated inside-out patches from hypothalamic neurones is the same as the channel activated by an increase in the concentrat ion of extracellular glucose in cell-attached recordings from glucose- sensitive neurones.