Interactions of adenosine and magnesium on rat hippocampal slices

The potency of adenosine in reducing orthodromically evoked population potentials elicited in area CA1 of rat hippocampal slices was greatly reduced by removal of magnesium from the bathing medium. Removal of magnesium increased cell excitability, but this did not account for the loss of potency as the addition of (+/-)-2-amino-5-phosphonovaleric acid (2-APV), or a reduction in extracellular calcium failed to restore adenosine inhibition. However, addition of cobalt (500 microM) did restore inhibition. The results may indicate a requirement for magnesium, or a similar divalent cation, at the A1-inhibitory adenosine receptor. The observation of excitation by adenosine in zero magnesium/low calcium may suggest an A2-excitatory receptor interaction in the absence of adenosine inhibition.