Presynaptic diadenosine polyphosphate receptors: Interaction with other neurotransmitter systems

Abstract

Diadenosine polyphosphates (ApnA n = 2–6) are natural compounds that can play a neurotransmitter role in the synaptic terminals of the central nervous system. Microfluorimetric studies of [Ca2+]i in single synaptic terminals have shown the presence of specific ionotropic receptors for nucleotides and dinucleotides. These dinucleotide receptors may or may not coexist at the same terminal. Aminergic terminals from rat basal ganglia have been immunologically characterised by the presence of the vesicular monoamine transporter 2 after the functional studies. Fifty‐eight percent of these terminals respond to nucleotides, and of these, 17% respond only to Ap5A. Cholinergic terminals from rat midbrain were immunologically characterised by the vesicular acetylcholine transporter. Sixty‐three percent of these terminals responded to nucleotides, and of these, 22% responded only to Ap5A. The presynaptic ionotropic dinucleotide receptors can coexist not only with the ATP receptors, but also with various subtypes of nicotinic receptors. GABAergic terminals from rat midbrain were immunologically characterised by the vesicular inhibitory amino acid transporter. Fifty‐nine percent of these terminals responded to nucleotides, and of these, 17% responded only to Ap5A. The presynaptic dinucleotide receptors, when stimulated, are able to induce the GABA release from synaptosomal preparations. These data clearly show the broad interaction of nucleotides and dinucleotides with other neurotransmitter systems.