Affiliation:
1. Department of Biomedical Science, McMaster University, Hamilton L8N 3Z5; and
2. Department of Medicine, University of West Ontario, London, L6A 5A5 Ontario, Canada
Abstract
In canine ileum we investigated the distribution of pituitary adenylate cyclase-activating peptide (PACAP), using immunofluorescence and radioimmunoassay and the binding of 125I-PACAP-27 to membranes. Nerve profiles immunoreactive to PACAP-27, and often to vasoactive intestinal polypeptide (VIP) as well, were found in all plexi, but PACAP was present in ∼100-fold lesser amounts than VIP. High-performance liquid chromatography analysis of deep muscular plexus (DMP) synaptosomes suggested the presence of PACAP-38, PACAP-27, and a third unidentified molecular form. High- and low-affinity125I-PACAP-27 binding sites were found in DMP synaptosomes and circular smooth muscle (CM) plasma membranes. In competition studies with DMP membranes, high (H)- and low (L)-affinity dissociation constants ( K d) and maximal binding capacities (Bmax) were as follows: K d H = 66.9 pM, Bmax H = 101 fmol/mg; K d L = 2.18 nM, Bmax L = 580 fmol/mg protein. The binding of125I-PACAP-27 was fast. Dissociation was slow and incomplete in the presence of unlabeled PACAP-27 but accelerated by pretreatment with guanosine 5′- O-(3-thiotriphosphate) (GTPγS). GTPγS or cholera toxin treatment eliminated high-affinity binding in both membranes. VIP had ∼100-fold lower affinity than PACAP-27 in both membranes. Cross-linking studies identified an ∼70-kDa PACAP receptor in each membrane. Thus PACAP coexists with VIP in ileal enteric nerves and acts on PACAP-preferring, possibly Gs-coupled, receptors in DMP synaptosomes and CM membranes.
Publisher
American Physiological Society
Subject
Physiology (medical),Gastroenterology,Hepatology,Physiology
Cited by
14 articles.
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