IDENTIFICATION OF A 5-HYDROXYTRYPTAMINE (5-HT2) RECEPTOR ON GUINEA-PIG SMALL-INTESTINAL CRYPT CELLS

Radioligand labeling of [H-3]ketanserin was examined in suspensions of dispersed guinea pig small intestinal mucosal cells prepared by modification of the EDTA-chelation method described by M. M. Weiser (J. Biol. Chem. 248: 2536-2541, 1973). Preferential incorporation of [H-3]thymidine was used to confirm that suspensions were enriched in crypt cells. At 25-degrees-C, binding of [H-3]ketanserin to dispersed enterocytes was rapid, maximal by 5 min, saturable (dissociation constant = 1.5 nM), 65 +/- 5% specific, stable, and reversible. The maximal number of binding sites per cell was 92,000 (range 86,000-105,500). Binding was temperature dependent, with maximal binding at 37-degrees-C, and was inhibited by 5-hydroxytryptamine (5-HT) (half-maximal inhibition of [H-3]ketanserin binding observed in response to 1 muM 5-HT) and ketanserin (half-maximal inhibition of [H-3]ketanserin binding observed in response to 1 nM ketanserin) but not by the 5-HT1p antagonist N-acetyl-5-hydroxytryptophyl 5-hydroxytryptophan amide (5-HTP-DP) or the 5-HT3 antagonist 3-tropanyl-indole-3-carboxylate methiodide (ICS-205-930). The second messenger system coupled to the putative mucosal 5-HT2 receptor was examined. 5-HT stimulated a concentration-dependent production of inositol 1,4,5-trisphosphate (IP3) in the dispersed enterocytes. This was maximal at 1 min and was inhibited in a concentration-dependent manner by ketanserin. 5-HTP-DP and ICS-205-930 had no effect on 5-HT-stimulated production Of IP3. These data provide evidence for the existence of a mucosal 5-HT2 receptor located on guinea pig small intestinal crypt cells.