Species differences in characteristics and distribution of [3H] alpha,beta-methylene ATP binding sites in urinary bladder and urethra of rat, guinea-pig and rabbit.

The characteristics and distribution of [3H] alpha,beta-methylene ATP ([3H] alpha,beta-MeATP, a radioligand for P2x-purinoceptors) binding sites in the urinary bladder of rat, guinea-pig and rabbit were examined. Autoradiographic localization of [3H] alpha,beta-MeATP binding sites was also carried out on the urethra of the three species. Receptor binding assay showed that the rat bladder possesses the highest density of specific binding sites, followed by rabbit and guinea-pig bladder. Semi-quantitative analysis of autoradiograms showed that the grain densities in the bladders of rat, guinea pig, and rabbit were parallel to those obtained from receptor binding assay. The grain densities were greatly reduced in the presence of beta,gamma-methylene ATP (beta,gamma-MeATP). No significant specific binding was detected in the smooth muscle of rat and guinea-pig urethra, while a very low level of specific binding was observed in the rabbit urethra. Differences of grain densities in different regions (dome, body, and trigone) of the same bladder were also observed, but they were not as remarkable as those between species. The results of this study demonstrate species differences of P2X-purinoceptor densities in the urinary bladder, which may reflect differing degrees of purinergic neurotransmitter control of the bladder detrusor muscle.