Adenosine triphosphate and diadenosine pentaphosphate induce [Ca2+]i increase in rat basal ganglia aminergic terminals

Abstract

Synaptosomal preparations from rat midbrain exhibit specific responses to both ATP and Ap5A, which stimulate a [Ca2+]i increase in the presynaptic terminals via specific ionotropic receptors, termed P2X, and diadenosine polyphosphate receptors. Aminergic terminals from rat brain basal ganglia were characterized by immunocolocalization of synaptophysin and the vesicular monoamine transporter VMAT2 and represent 29% of the total. These aminergic terminals respond to ATP and/or Ap5A with an increase in the intrasynaptosomal calcium concentration as measured by a microfluorimetric technique. This technique, which allows single synaptic terminals to be studied, showed that roughly 8.2% ± 1.6% of the aminergic terminals respond to ATP, 16.9% ± 1.3% respond to Ap5A, 32.6% ± 0.8% to both, and 42.3% ± 1.5% of them have no response. Immunological studies performed with antibodies against ionotropic ATP receptor subunits showed positive labelling with anti‐P2X3 antibodies in 39% of the terminals. However, colocalization studies of VMAT and P2X3 receptor subunit indicate that only 25% of the aminergic terminals also contain this receptor subtype. These results demonstrate that the aminergic terminals from the rat brain basal ganglia are to a large extent under the modulation of presynaptic nucleotide and dinucleotide receptors.