Recent evidences from molecular biology, radioreceptor binding and functional studies indicate that the α1-adrenoceptor population is heterogeneous and can at least be divided into two subclasses named α1A and α1B. The present study was designed to obtain, a selective enrichment of rat brain cortical membranes with each subtype of α1-adrenoceptor using alkylating agents. [3H]prazosin binding to rat cortical membranes was saturable and of high affinity (KD = 0.11 ± 0.02 nM; Bmax = 132.5 ± 7.2 fmol/mg protein). All ligands competed for specific [3H]prazosin binding in a statistically significant biphasic manner (%Rhigh = 30-40%; % Rlow = 60-70%). These sites meet generally accepted and recently described pharmacologic criteria for their identification as the α1A- and α1B-adrenoceptors. After pretreatment of membranes with benextramine (1 μM) in the presence of clonidine (1 μM), the antagonists, WB4101, (+)-niguldipine and phentolamine, displaced the radioligand with an inhibition curve steeper than in control membranes and with Ki values that agree with those obtained for the low affinity site present in control membranes. On the other hand, after pretreatment with chloroethylclonidine (10 μM) in the presence of WB4101 (1 nM), Hill coefficients for the displacement of the radioligand by WB4101, (+)-niguldipine, and phentolamine, were also increased, but in contrast to the situation described above, the Ki values agree with those obtained for the high affinity site present in control membranes. In conclusion, this method of partial alkylation of receptors could be a valuable tool for separately studying the pharmacological characteristics of the α1-adrenoceptor subtypes in native membranes of cerebral tissue. © 1994.
|Journal||European Journal of Pharmacology: Molecular Pharmacology|
|Publication status||Published - 15 Feb 1994|
- Cerebral cortex
- [ H]Prazosin 3
- α-Adrenoceptor subtype