TOLBUTAMIDE BLOCKS POSTSYNAPTIC BUT NOT PRESYNAPTIC EFFECTS OF ADENOSINE ON HIPPOCAMPAL CA1 NEURONS

Extracellular recording in the CA1 pyramidal cell layer of rat hippoca mpal slices was used to examine the effect of the ATP-sensitive potass ium channel blocker tolbutamide and the channel opener levcromakalim o n responses to adenosine. Tolbutamide 1mM blocked the inhibitory effec t of adenosine on the size of orthodromic population spikes but had no effect on the inhibitory action of adenosine on field EPSPs. Tolbutam ide also blocked the suppression by adenosine of repetitive antidromic spikes induced in calcium-free media with high magnesium but did not prevent the effects of baclofen. Levcromakalim 100 mu M potentiated in hibitory effect of adenosine, but not baclofen, on orthodromic populat ion spikes. The results show that at postsynaptic, but not presynaptic , sites adenosine may activate an ATP-sensitive potassium channel.