Exendin-4 and exendin-(9-39)NH2: agonist and antagonist, respectively, at the rat parietal cell receptor for glucagon-like peptide-1-(7-36)NH2.
Exendin-4 is a novel peptide from Heloderma suspectum venom which is 53% homologous with glucagon-like peptide-1 GLP-1-(7-36)NH2, a stimulant of cAMP-dependent H+ production in rat parietal cells. It was the aim of the present study to determine whether this effect of GLP-1-(7-36)NH2 is shared by exendin-4, and whether the responses to either peptide are blocked by exendin-(9-39)NH2, a competitive specific exendin receptor antagonist. In enriched rat parietal cells H+ production was measured indirectly by [14C]aminopyrine accumulation. cAMP production was determined by radioimmunoassay. [125I]GLP-1-(7-36)NH2 was prepared using chloramine T followed by high pressure liquid chromatography (HPLC) purification. Exendin-4 (10(-12) - 10(-8) M) stimulated [14C]aminopyrine accumulation in a concentration-dependent manner (EC50 = 7.6 x 10(-11) M). At the maximally effective concentration (10(-9) M) exendin-4 was as effective as GLP-1-(7-36)NH2 reaching 70-80% of the response to 10(-4) M histamine. Likewise, exendin-4 (10(-11) - 10(-7) M) stimulated parietal cell cAMP production up to 2.8-fold. Maximal stimulation by exendin-4 of [14C]aminopyrine accumulation was not affected by ranitidine (10(-4) M), but was concentration-dependently reduced by exendin-(9-39)NH2 (10(-11) - 10(-7) M). At the maximal concentration, exendin-(9-39)NH2 completely abolished the responses to 10(-9) M exendin-4 and to 10(-9) M GLP-1-(7-36)NH2 while not altering stimulation by 10(-4) M histamine. Binding of [125I]GLP-1-(7-36)NH2 to enriched parietal cells was displaced by exendin-4 (Ki = 4.6 x 10(-10) M) as well as by exendin-(9-39)NH2 (Ki = 4.0 x 10(-9) M).(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Internal Medicine II, Technical University of Munich, Germany.
W
W
Schepp
J
J
Schmidtler
T
T
Riedel
K
K
Dehne
V
V
Schusdziarra
J J
JJ
Holst
J
J
Eng
J P
JP
Raufman
M
M
Classen
D000632:Aminopyrine / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D000077270:Exenatide; D005260:Female; D005744:Gastric Acid / Q000378:metabolism; D005934:Glucagon / Q000378:metabolism*; D052216:Glucagon-Like Peptide 1; D004763:Glucagon-Like Peptides; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D008116:Lizards / Q000502:physiology*; D010295:Parietal Cells, Gastric / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology*; D010455:Peptides / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D018027:Receptors, Glucagon / Q000819:agonists* / Q000037:antagonists & inhibitors*; D014688:Venoms / Q000494:pharmacology*
D003432:Cross-Linking Reagents; D010446:Peptide Fragments; D010455:Peptides; D018027:Receptors, Glucagon; D014688:Venoms; D000632:Aminopyrine; C083773:exendin (9-39); D004763:Glucagon-Like Peptides; D006632:Histamine; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; C055454:glucagon-like peptide 1 (1-36)amide; D000077270:Exenatide; D000242:Cyclic AMP