Differential activation of adenylate cyclase by secretin and VIP receptors in the calf pancreas.
OBJECTIVE
Secretin is a key regulator of pancreatic secretion, but the molecular basis of its action is not well understood, especially in the calf pancreas. Our study investigated the expression and functional competence of secretin receptors (SEC-R) in calf pancreatic membranes.


METHODS
We used reverse transcriptase-polymerase chain reaction, sequencing, and Northern blot to assess the expression of the SEC-R gene. The functional characterization of SEC-R was accomplished using adenylate cyclase (AC) assay.


RESULTS
We successfully amplified, by reverse transcriptase-polymerase chain reaction, a fragment of the SEC-R gene from 119-day-old calf pancreas. This sequence shows higher homology with SEC-R than with vasoactive intestinal polypeptide (VIP)-1 and VIP-2 receptors from other species. Northern blot analysis detected a 1.8-kb transcript. Accordingly, secretin stimulates AC activity in calf pancreatic membranes isolated from 28- and 119-day-old animals with a potency (Ka) of 1.9 to 2.7 nmol/L. Maximal AC stimulation induced by secretin represented a 3- to 4-fold increase of basal activity. AC activation by secretin was inhibited by the 2 SEC-R antagonists, [psi4,5] secretin (l micromol/L) and [5-27] secretin (10 micromol/L). Interestingly, [psi4,5] secretin was ineffective against VIP-induced AC stimulation.


CONCLUSIONS
Our data indicate that secretin exerts a direct action on pancreatic secretion through specific SEC-R coupled to the AC system. Calf pancreatic SEC-Rs are coexpressed with VIP-2 receptors that we previously identified by ligand binding and cross-linking experiments.
Meuth-Metzinger
Valérie Le
VL
Université Paris 13, Faculté de Médecine, Laboratoire de Pharmacologie Expérimentale et Clinique, Bobigny CEDEX, France.
Philouze-Rome
Véronique
V
Metzinger
Laurent
L
Gespach
Christian
C
Guilloteau
Paul
P
D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D015870:Gene Expression / Q000502:physiology; D008969:Molecular Sequence Data; D010179:Pancreas / Q000254:growth & development / Q000378:metabolism*; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide / Q000494:pharmacology; D043562:Receptors, G-Protein-Coupled / Q000235:genetics* / Q000378:metabolism; D011964:Receptors, Gastrointestinal Hormone / Q000235:genetics* / Q000378:metabolism; D051239:Receptors, Vasoactive Intestinal Peptide, Type II / Q000235:genetics / Q000378:metabolism*; D051238:Receptors, Vasoactive Intestinal Polypeptide, Type I / Q000235:genetics / Q000378:metabolism*; D012633:Secretin / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D043562:Receptors, G-Protein-Coupled; D011964:Receptors, Gastrointestinal Hormone; D051239:Receptors, Vasoactive Intestinal Peptide, Type II; D051238:Receptors, Vasoactive Intestinal Polypeptide, Type I; C029937:secretin receptor; D012633:Secretin; D014660:Vasoactive Intestinal Peptide; D000262:Adenylyl Cyclases