Modulatory role of adenosine receptors in insect motor nerve terminals.

The effects of adenosine and ATP were studied on blowfly larvae Calliphora vicina neuromuscular preparation. Adenosine diminished (IC50 = 40 +/- 3 microM) the amplitude of nerve-evoked postsynaptic currents (EPSCs) and slightly decreased the frequency of spontaneous currents without affecting their amplitude. EPSCs were slightly reduced by ATP, and this effect was prevented by concanavalin A. Presynaptic inhibition by adenosine was temperature-dependent and insensitive to pertussis toxin. A1 agonists of vertebrate adenosine receptor CPA and NECA failed to reproduce the effect of adenosine, and 2-CADO enhanced the EPSCs. A1 antagonist DPCPX competitively inhibited adenosine action. A2 agonist DPMA potentiated EPSCs, and its effect was abolished by A2 antagonist DMPX. Adenosine and ATP failed to affect the nonquantal release of glutamate. The results show for the first time the presence of presynaptic adenosine receptors regulating transmitter release at insect motor nerve terminals and point to differences in pharmacological properties of adenosine receptor subtypes in insects and vertebrates.