Characterization of alpha 1-adrenoceptor subtypes labeled by [3H]prazosin in single cells prepared from rabbit...

alpha 1-Adrenoceptor agents with alpha 1-adrenoceptor subtypes sensitive and insensitive to inactivation by chloroethylclonidine were characterized in single cells prepared from rabbit thoracic aorta. WB 4101, 5-methylurapidil and spiperone interacted with high- and low-affinity sites labeled by [3H]prazosin. Chloroethylclonidine 10 microM pretreatment eliminated the low-affinity sites of displacement curves obtained with WB 4101 and 5-methylurapidil but had no effect on the high-affinity site for these agents. The treatment also reduced the site of the displacement curve obtained with spiperone but eliminated only the high-affinity site. Methoxamine and clonidine, alpha-adrenoceptor agonists, interacted with binding sites labeled by [3H]prazosin. The displacement curve for methoxamine was not affected by chloroethylclonidine 10 microM pretreatment, while that for clonidine was partially eliminated by the same type of pretreatment. These results suggest that, in single cells prepared from rabbit thoracic aorta: (1) WB 4101, 5-methylurapidil and spiperone interact with differing affinity at sites labeled by [3H]prazosin; (2) chloroethylclonidine-sensitive and -insensitive [3H]prazosin binding sites correspond to those with low- and high-affinity sites for WB 4101 and 5-methylurapidil, and a high- and low-affinity for spiperone, respectively; and (3) chloroethylclonidine treatment was shown to have no effect on the displacement curve of methoxamine but a partial effect on that of clonidine.