Tolbutamide blocks postsynaptic but not presynaptic effects of adenosine on hippocampal CA1 neurones

Extracellular recording in the CA1 pyramidal cell layer of rat hippocampal slices was used to examine the effect of the ATP-sensitive potassium channel blocker tolbutamide and the channel opener levcromakalim on responses to adenosine. Tolbutamide 1 mM blocked the inhibitory effect of adenosine on the size of orthodromic population spikes but had no effect on the inhibitory action of adenosine on field EPSPs. Tolbutamide 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 microM potentiated inhibitory effect of adenosine, but not baclofen, on orthodromic population spikes. The results show that at postsynaptic, but not presynaptic, sites adenosine may activate an ATP-sensitive potassium channel.