title: Characterization of somatostatin binding sites in cytosolic fraction of rat intestinal mucosa.
abstract: Specific binding sites for somatostatin have been characterized in cytosolic fraction of rat intestinal mucosa by using 125I-labelled Tyr11-somatostatin and a variety of physicochemical conditions. The binding depended on time, temperature and pH, and was reversible, saturable and specific. At apparent equilibrium, the specific binding of 125I-Tyr11-somatostatin was competitively inhibited by native somatostatin in the 1 nM-4 microM concentration range. Binding studies suggested the presence of two classes of binding sites: a class with high affinity (Kd = 0.07 microM) and low capacity (4.6 pmol/mg protein) and a class with low affinity (Kd = 1.05 microM) and high capacity (277 pmol/mg protein) at 25 degrees C. Somatostatin exhibited competitive inhibition of tracer binding, while neuropeptides such as neurotensin, substance P, Leu-enkephalin, and vasoactive intestinal peptide were ineffective. The presence of somatostatin binding sites in cytosolic fraction of intestinal mucosa, together with the known occurrence of somatostatin in D-cells and nerve endings in the small intestine, strongly suggest that this peptide may be involved in the physiology and physiopathology of intestinal epithelium.
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002118:Calcium / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013004:Somatostatin / Q000031:analogs & derivatives / Q000378:metabolism*
chemical_list: D013004:Somatostatin; C032367:somatostatin, Tyr(11)-; D008274:Magnesium; D002118:Calcium