Exendin-3, a novel peptide from Heloderma horridum venom, interacts with vasoactive intestinal peptide receptors and a newly described receptor on dispersed acini from guinea pig pancreas. Description of exendin-3(9-39) amide, a specific exendin receptor antagonist.

J P Raufman,L Singh,J Eng

doi:10.1016/s0021-9258(18)49932-2

Abstract

Exendin-3 increased cellular cAMP levels and amylase release from dispersed acini from guinea pig pancreas. Low concentrations (0.1-3 nM) caused a 12-fold increase in cAMP, whereas higher concentrations (0.3-3 microM) caused an additional 24-fold increase in cAMP. Maximal cAMP with the highest concentration tested was the same as the maximal response with secretin, vasoactive intestinal peptide (VIP), peptide histidine isoleucine, helodermin, or helospectin-I. In terms of amylase release, exendin-3 had the same efficacy but was the least potent of these peptides. Exendin-3-induced increases in amylase release were inhibited by VIP receptor antagonists and the new peptide (greater than 0.1 microM) competed with radiolabeled VIP for binding sites on dispersed acini. Increasing concentrations of an exendin-3 fragment, exendin-3(9-39) amide, did not increase cAMP or amylase release but inhibited the increase in cAMP observed with 0.1-3 nM exendin-3. The fragment did not alter the effects of other peptides that are known to increase acinar cAMP. We conclude that exendin-3 interacts with at least two receptors on guinea pig pancreatic acini; at high concentrations (greater than 100 nM) the peptide interacts with VIP receptors, thereby causing a large increase in cAMP and stimulating amylase release; at lower concentrations (0.1-3 nM) the peptide interacts with a putative exendin receptor, thereby causing a smaller increase in cAMP of undetermined function. Exendin-3(9-39) amide is a specific exendin receptor antagonist.

Highlights

From the $Departmentof Medicine, Division of Digestive Diseases, State University of New York-Health Science Center Brooklyn, New York 11203-2098 and the 1[SolomonA
To elucidate the nature of these interactions, we examined the actions of exendin-3 on dispersed endin-3-induced increases inamylase release were in- acini from guinea pig pancreas and compared these actions hibited by vasoactive intestinal peptide (VIP) receptor antagonists and thenew pep- with those of VIP, secretin,PHI, andbioactive peptides from tide (>0.1 p ~ c)ompeted with radiolabeled VIPfor Helodermatidae venoms
Initial experimentsshowed that exendin-3 increasedcellular cAMP and stimulated amyrlealseease from dispersedacini (5)

Summary

Introduction

From the $Departmentof Medicine, Division of Digestive Diseases, State University of New York-Health Science Center Brooklyn, New York 11203-2098 and the 1[SolomonA. 0 a cw n we examined the first phase of exendin-3-induced increases in cAMP that is not associated with stimulation of amylase release (0.1-3 nM exendin-3).To provide further evidence that the first phase of the exendin-3 cAMP dose-response curve is not due to interaction of the new peptide with VIP receptors, we examined the effect of combining VIPand exendin-3 (Table I). ActionsPOaAfnEcrixOneeianntdicin-3 preferring receptors thadto not mediate amylaserelease (16), we examined the effect of adding increasing concentrations of exendin-3 to 1 nM secretin.

Results

Conclusion