Possible Involvement of ATP-Sensitive K⁺ Channels in the Inhibition of Rat Central Adrenergic Neurotransmission under Hypoxia

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By using rat brain cortical slices preloaded with [³H]norepinephrine, we examined whether ATP-sensitive K⁺ channels are involved in altered adrenergic neurotransmission during hypoxia. The tritium overflow evoked by transmural nerve stimulation (TNS) was significantly inhibited at 5 min of hypoxia and reached the maximum inhibition at 20 min. The inhibition of the TNS-evoked tritium overflow under a 20-min hypoxia was reversed by subsequent reoxygenation and was concentration-dependently antagonized by glibenclamide (0.1 and 1 μM). ⁸⁶Rb⁺ efflux was increased after introduction of hypoxia and reached the peak value at about 20 min, which was concentration-dependently antagonized by glibenclamide (0.1-10 μM). Hypoxia decreased cortical ATP content. Linear correlations were mutually observed among the changes by hypoxia in the TNS-evoked tritium overflow, tissue ATP content and ⁸⁶Rb⁺ efflux. The spontaneous tritium outflow was inhibited only after hypoxic periods of more than 16 min, the inhibition being reversed by reoxygenation and antagonized by 1 μM glibenclamide. These results suggest that the inhibition of rat central adrenergic neurotransmission during hypoxia may be associated with an activation of ATP-sensitive K⁺ channels.