Distribution of [3H] alpha, beta-methylene ATP binding sites in pulmonary blood vessels of different species.

Purinergic neurotransmission has been reported to take part in the regulation of pulmonary vascular resistance in many species. The receptor which mediates the contraction of blood vessels by ATP was defined as P2X-purinoceptors in pharmacological studies. In the present study, autoradiographic localization of P2X-purinoceptors was carried out in pulmonary blood vessels from rat, guinea-pig, rabbit, piglet and human by using [3H] alpha, beta-methylene ATP ([3H] alpha, beta-MeATP) as the radioligand. Autoradiographs showed that all the pulmonary arteries had been labelled with [3H] alpha, beta-MeATP. The specific 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, both regional and interspecific. Generally, intrapulmonary arteries were labelled more heavily than the main pulmonary arteries, and the medium- and small-sized arteries had higher densities of P2X-purinoceptor than the large muscular arteries. The veins were sparsely labelled, except that rat intrapulmonary veins were labelled moderately. The results from this study provide: (1) direct evidence for the existence of P2X-purinoceptors in pulmonary vasculature, (2) a semi-quantitative estimation of the relative density of P2X-purinoceptors in pulmonary vessels of different sizes; and (3) a comparison of the P2X-purinoceptor densities among the species studied. Furthermore, the distribution of the P2X-purinoceptors is consistent with known pharmacological responses elicited by ATP in these vessels.