Heterogeneous 3H-rauwolscine binding sites in rat complex: two alpha2-adrenoceptor subtypes or and additional non-adrenergic interaction

Ligand binding and isolated tissue data have provided evidence for the existence of two, tissue-specific, alpha2-adrenoceptor in various rodent and non-rodent species. Thus, it has been proposed that the complex binding of alpha2-antagonists to rat cortical membranes is due to the presence of both subtypes in this tissue. The authors have previously shown that the alpha2-antagonist 3H-rauwolscine binds to two sites on rat cortical membranes: a high affinity component characterized pharmacologically as an alpha2-binding site, and a low affinity, spiperone-sensitive, serotonergic-like component. By the use of computerized non-linear curve fitting, and the inclusion of a concentration of spiperone previously shown to selectively occlude the low affinity component of the 3H-rauwolscine saturation isotherm, they have determined the rank order of affinity at each of the two sites. Whereas the rank order of affinity at the high affinity site retains the pharmacological profile of a single, monophaisc alpha2-binding-site, that at the low affinity component is markedly different and is similar to that at the putative 5HT subtype