Heterogeneous distribution of [3H]alpha,beta-methylene ATP binding sites in blood vessels

A radioligand binding assay and autoradiographic localisation of P2X-purinoceptors were carried out in several different blood vessels from rat, guinea-pig and rabbit by using [3H]alpha,beta-methylene ATP ([3H]alpha,beta-MeATP) as the radioligand. The radioligand binding assay on rabbit ear artery showed that the binding process was saturable, and a high density of P2X-purinoceptors was observed. Autoradiographic localisation showed that the specific [3H]alpha,beta-MeATP binding sites were only associated with the smooth muscle of the blood vessels. Semi-quantitation of the autoradiographs revealed significant differences in the densities of P2X-purinoceptors amongst the vessels studied. Generally the medium- and small-sized arteries had higher densities of P2X-purinoceptor than the elastic and large muscular arteries. In some large muscular arteries, such as the rabbit carotid, renal, hepatic and mesenteric, the outer region of vessel had a higher density of receptors than the inner region. The veins in this study were sparsely labelled, except portal veins where the longitudinal and circular layers of muscles were found to have different densities of P2X-purinoceptors. The results from this study provide direct evidence for the existence of P2X-purinoceptors in blood vessels; furthermore, the distribution of the P2X-purinoceptors is consistent with known pharmacological responses elicited by ATP in these vessels.