Co-localisation of functional nicotinic and ionotropic nucleotide receptors in isolated cholinergic synaptic terminals

The combination of immunological and microfluorimetric techniques has permitted the identification and analysis of the Ca2+ influx responses in single rat midbrain cholinergic terminals. These terminals represent 22% of the total synaptosomal population and about 63% of them responded to nucleotides by a Ca2+ influx. The nucleotide response distribution in cholinergic synaptic terminals is as follows; 22.4% to diadenosine pentaphosphate (Ap(5)A). 24.7% to adenosine 5'-triphosphate (ATP) and 16.3% to both agonists. The ATP and Ap(5)A are able to induce acetylcholine release in a dose- and calcium-dependent way, being the EC50 values 0.22 +/- 0.1 muM and 1.5 +/- 0.1 muM respectively. Specific inhibitors can block this secretory effect. The studies of Ca2+ influx responses in isolated single synaptic terminals have also permitted to demonstrate the wide co-expression of functional nicotinic and nucleotidic receptors. The percentage values of the terminals responding to both ATP/nicotine and Ap(5)A/nicotine were 18.4% and 19.1%, respectively, considering the total population. Immunological studies also confirmed the presence of P2X(3) subunits and alpha4 and alpha7 nicotinic receptor subunits in about 36%, 30% and 20%, respectively, of the cholinergic terminals. (C) 2002 Elsevier Science Ltd. All rights reserved.