Identification of nonsulfated cholecystokinin-58 in canine intestinal extracts and its biological properties

Abstract

Nonsulfated CCK58[CCK58(ns)] has not been considered to be of biological importance because CCK58(ns) binds poorly to the CCKAreceptor and has only been identified once in intestinal extracts. In this work, a radioimmunoassay specific for the COOH-terminal region of gastrin and CCK (antibody 5135) was used to monitor the purification of CCK molecular forms from canine intestinal extracts. A minor immunoreactive peak was associated with a major absorbance peak during an ion-exchange, HPLC step. Characterization of this minor immunoreactive peak demonstrated that it was CCK58(ns). CCK58(ns) is 14% as immunoreactive as sulfated CCK8[CCK8(s)]. Amino acid analysis demonstrated that CCK58(ns) was present at 50% the amount of CCK58(s). In addition, we found that CCK58(ns) does not potently displace an125I-labeled CCK10analog from the CCKAreceptor in mouse pancreatic membranes and does not stimulate amylase release from isolated pancreatic acini, or stimulate pancreatic secretion in an anesthetized rat model. By contrast, CCK58(ns) does bind to CCKBreceptors and stimulates gastric acid secretion via this receptor. The presence of CCK58(ns) and its ability to selectively stimulate the CCKBreceptor without stimulation of the CCKAreceptor suggest that CCK58(ns) may have unique physiological properties, especially tissues where the nonsulfated peptide can act as a paracrine or neurocrine agent.