Studies on rat intestinal epithelial cell receptors for serotonin and opiates.

We have employed the receptor-ligand binding technique in an attempt to determine if specific binding sites (receptors) for serotonin and opiates are present on rat intestinal epithelial cell membranes. A wide variety of ligands for serotonin and opiate receptors bound to specific receptor sites in rat brain. However, the same ligands failed to bind in a specific (receptor-related) manner to isolated membranes of rat ileal and colonic cells. Additional washing of the tissue pellet (to remove soluble peptidases), pretreatment with p-chlorophenylalanine (to deplete endogenous serotonin), alteration of sodium concentration (to antagonize the effects of putative endogenous inhibitors of opiate ligand binding), changes in incubation time, temperature, tissue protein and tritiated ligand concentration failed to yield meaningful results with the enterocyte membranes. We conclude that, as assessed under the present conditions, serotonergic and opiate receptors are not present or are not accessible on rat intestinal epithelial cell membranes.