RADIOLIGAND BINDING AND AUTORADIOGRAPHIC VISUALIZATION OF ADENOSINE TRANSPORT SITES IN HUMAN INFERIOR VAGAL GANGLIA AND THEIR AXONAL-TRANSPORT ALONG RAT VAGAL AFFERENT NEURONS

The present study has employed membrane-binding studies and in vitro a utoradiography to demonstrate the presence of adenosine transport site s in human inferior vagal ganglia using [H-3]nitrobenzylthioinosine ([ H-3]NBMPR), a potent inhibitor of adenosine transport. In addition, [H -3]NBMPR was used to determine whether adenosine transport sites are s ubject to axonal transport along the rat vagus nerve. Binding of [H-3] NBMPR to human inferior vagal ganglia membranes was saturable and reve rsible. Saturation experiments revealed a single class of high affinit y-binding sites with a K-d of 93.73 +/- 23.13 pM and B-max of 413.50 /- 50.40 fmol/mg protein. In displacement experiments, the adenosine t ransport inhibitor dipyridamole was the most potent displacer of [H-3] NBMPR binding (K-i = 42.7 +/- 28.0 nM). Adenosine itself was able to f ully displace [H-3]NBMPR binding with a K-i of 115.0 +/- 34.0 mu M. Th e A(1)/A(2a) adenosine receptor agonist 5'-(N-ethylcarboxamido)-adenos ine (NECA) was able to fully displace [H-3]NBMPR binding in only one e xperiment at a concentration of 100 mu M, yielding an affinity 1000-fo ld higher than its affinity for adenosine receptors. All competition c urves obtained from displacement experiments displayed monophasic prof iles, indicating the presence of a single class of [H-3]NBMPR binding sites. Incubation of human inferior vagal ganglia sections with [H-3]N BMPR (0.7 nM) revealed dense binding which appeared to be consistent w ith the distribution of neuronal cell bodies in this tissue. Following unilateral ligation of the vagus nerve in the rat, acccumulation of [ H-3]NBMPR binding sites occurred both proximal and distal to the vagal ligatures. These results suggest that [H-3]NBMPR binds with high affi nity to a single class of adenosine transport sites, and that these si tes are present on vagal afferent neurons in the human and undergo bid irectional axonal transport along the rat vagus nerve.