Adenosine-mediated synaptic inhibition: partial blockade by barium does not prevent anti-epileptiform activity

Adenosine-induced inhibition of evoked postsynaptic potentials (PSPs) and epileptiform burst firing in the CA1 subfield of rat hippocampal slices was studied with intracellular recordings in vitro. Adenosine (50 microM) caused a membrane hyperpolarization which was abolished during superfusion with 2 mM Ba2+. The adenosine-induced inhibition of the PSPs was still evident, although the magnitude of the effect was significantly reduced. Adenosine also reduced Ba(2+)-induced burst firing, but less effectively than it did bursts evoked by TEA (5 mM). The results suggest that adenosine inhibits synaptic transmission and epileptiform activity by at least 2 mechanisms: a postsynaptic barium-sensitive increase in gK and a presynaptic effect independent of this adenosine-evoked outward potassium conductance.