Presence of different ATP receptors on rat midbrain single synaptic terminals. Involvement of the P2X(3) subunits

Adenosine 5'-triphosphate (ATP) stimulates a [Ca2+](i) increase via specifi c ionotropic receptors, termed P2X receptors, in rat midbrain presynaptic t erminals. A microfluorimetric technique enabled study of the [Ca2+](i) incr ease in isolated single synaptic terminals, showing that 33.4 +/- 2.5% of t hem responded to ATP. Immunological studies carried out, after functional s tudies, with specific anti-P2X receptor subunit antibodies showed only posi tive labelling with anti-P2X(3) antibodies in 23.5 +/- 1.7% Of the terminal s. All positively P2X(3) labelled synaptic terminals responded to ATP. Neve rtheless, not all of them responded to alpha,beta -meATP, these representin g 6.7 +/- 1.5% of the total. In addition, 9.8 +/- 2.3% of the terminals res ponded to ATP but exhibit negative P2X(3)-labelling. These results demonstr ate the existence of a heterogeneous population of ionotropic ATP receptors at the presynaptic level. (C) 2001 Elsevier Science Ireland Ltd. All right s reserved.