Distribution of vasoactive intestinal polypeptide (VIP) binding in circular muscle and characterization of VIP binding in canine small intestinal mucosa.
The present study examined the localization and characterization of [125I]vasoactive intestinal polypeptide (VIP) binding to synaptosomes and enterocyte membranes using preparations made from homogenized canine intestinal mucosa and compared it to [3H]saxitoxin binding and VIP-immunoreactive content (markers for synaptosomes). The highest [125I]VIP binding was located in the P2 fraction and was correlated with the locations of maximal [3H]saxitoxin binding and VIP-immunoreactive content. This correlation indicates that VIP receptors are present on synaptosomes of canine small intestinal mucosa. A fraction enriched in synaptosomes contained a high density of saturable VIP receptors (352 +/- 26.40 fmol/mg) having high affinity (Kd, 0.23 nM) for [125I]VIP. Studies of association and dissociation of [125I]VIP to this site revealed that binding was fully reversible and yielded a Kd value similar to that from equilibrium binding. Competition binding experiments suggested the presence of two binding sites, a high and a low affinity binding site. The order of competition potency was VIP greater than peptide histidine isoleucine greater than secretin greater than peptide histidine methionine greater than or equal to [D-Ala4]VIP greater than or equal to [Phe1]VIP greater than VIP10-28 greater than [4-Cl-D-Phe6-Leu17]VIP. All these competitors displaced all specifically bound VIP. VIP, peptide histidine isoleucine and secretin interacted differentially with each of the two binding sites. Peptide histidine methionine, [D-Ala4]VIP, [Phe1]VIP, VIP10-28 and [4-Cl-D-Phe6-Leu17]VIP interacted with a single low affinity at all binding sites. Other VIP binding sites were sought in circular muscle and submucosa.(ABSTRACT TRUNCATED AT 250 WORDS)
Mao
Y K
YK
McMaster University, Department of Biomedical Sciences, Hamilton, Ontario, Canada.
Barnett
W
W
Coy
D H
DH
Tougas
G
G
Daniel
E E
EE
D000818:Animals; D001667:Binding, Competitive; D004285:Dogs; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000648:ultrastructure; D007421:Intestine, Small / Q000378:metabolism* / Q000648:ultrastructure; D007700:Kinetics; D009130:Muscle, Smooth / Q000378:metabolism / Q000648:ultrastructure; D011964:Receptors, Gastrointestinal Hormone / Q000378:metabolism; D018005:Receptors, Vasoactive Intestinal Peptide; D012530:Saxitoxin / Q000378:metabolism; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism*
D011964:Receptors, Gastrointestinal Hormone; D018005:Receptors, Vasoactive Intestinal Peptide; D012530:Saxitoxin; D014660:Vasoactive Intestinal Peptide