PT  - JOURNAL ARTICLE
AU  - H Paris
AU  - T Voisin
AU  - A Remaury
AU  - C Rouyer-Fessard
AU  - D Daviaud
AU  - D Langin
AU  - M Laburthe
TI  - Alpha-2 adrenoceptor in rat jejunum epithelial cells: characterization with [3H]RX821002 and distribution along the villus-crypt axis.
DP  - 1990 Sep 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 888--893
VI  - 254
IP  - 3
4099  - http://jpet.aspetjournals.org/content/254/3/888.short
4100  - http://jpet.aspetjournals.org/content/254/3/888.full
SO  - J Pharmacol Exp Ther1990 Sep 01; 254
AB  - Alpha-2 adrenergic receptivity of rat jejunum epithelial cells was studied using the new antagonist radioligand, [3H]RX821002 [( 3H]-2-(2-methoxy-1,4-benzodioxan-2-yl)-2-imidazoline). All the parameters of [3H]RX821002 binding were consistent with the labeling of an alpha-2 adrenoceptor. The use of this probe was moreover extremely convenient, because contrarily to [3H]yohimbine and [3H]rauwolscine, [3H]RX821002 displayed in this tissue a very high affinity (Kd = 0.54 +/- 0.12 nM) and a low level of nonspecific binding (5% at 1 nM [3H]RX821002). Competition studies with various antagonists and agonists showed that the labeled sites were alpha-2-selective and stereospecific. Oxymetazoline was much more potent than chlorpromazine or prazosin suggesting that the receptor is of the alpha-2-subtype. Yohimbine and rauwolscine were equipotent, which is also in agreement with the pharmacological definition of this subtype. These two compounds displayed, however, a rather weak affinity (Ki approximately 40 nM), which is somewhat different with what one should expect for a true alpha-2A adrenoceptor. Altogether the competition data indicated that the alpha-2 adrenoceptor from rat jejunal epithelium is neither an alpha-2A, nor an alpha-2B, nor an alpha-2c adrenoceptor and may belong to a fourth subtype.(ABSTRACT TRUNCATED AT 250 WORDS)