Distribution of glucagon receptors on hormone-specific endocrine cells of rat pancreatic islets.
Glucagon is insulinotropic, but it remains uncertain whether the insulinotropic action is mediated directly by glucagon receptors expressed on beta-cells or by cross-binding to the insulinotropic glucagon-like peptide-1 (GLP-1) receptor known to be expressed on beta-cells. Binding of [125I]glucagon to GLP-1 receptors and not to glucagon receptors has been reported in tumor-derived beta-cells (15). The objectives of the current study were to use receptor-binding techniques and a glucagon receptor-specific antiserum to determine whether glucagon receptors are present on beta-cells. Specific binding (7.2 +/- 0.8%) of [125I]GLP-1 to beta TC-3 cells was displaced equivalently with GLP-1 and exendin-(9-39) )Kd = 0.9 and 0.4 nM. respectively), whereas approximately 700-fold higher concentrations of glucagon were required for equal displacement (Kd = 400 nM). Binding of [125I]glucagon to beta TC-3 cells (approximately 1%) was displaced equivalently with 1 microM glucagon, GLP-1, or exendin-(9-39). These observations support earlier findings that beta TC-3 cells do not express functional glucagon receptors. However, specific binding of [125I]glucagon was observed on INS-1 cells (2.3 +/- 0.2%); this was displaced with glucagon (Kd = 1 nM), but not 1 microM GLP-1 or exendin-(9-39). To examine the distribution of glucagon receptors on native beta-cells, dispersed cultured rat islets were immunostained for glucagon, somatostatin, or insulin in combination with a polyclonal rabbit antiserum raised to an extracellular portion of the glucagon receptor (KD-14). The glucagon receptor antiserum colocalized staining with approximately 97% of immunoreactive insulin cells, 9% of immunoreactive glucagon cells, and 11% of immunoreactive somatostatin cells. Perfusion of the rat pancreas with concentrations of glucagon as low as 10(-12) M resulted in significant insulin release. These results suggest that whereas the tumor-derived beta-cell line beta TC-3 does not express functional glucagon receptors, INS-1 cells and isolated rat pancreatic beta-cells have specific glucagon receptors, as do a subpopulation of alpha- and delta-cells. A model is proposed for the role of glucagon in islet hormone secretion during feeding and fasting.
Laboratory of Molecular Endocrinology, Massachusetts General Hospital, Boston, USA.
T J
TJ
Kieffer
R S
RS
Heller
C G
CG
Unson
G C
GC
Weir
J F
JF
Habener
D000818:Animals; D001667:Binding, Competitive; D002460:Cell Line; D002478:Cells, Cultured; D004435:Eating; D005215:Fasting; D005260:Female; D005934:Glucagon / Q000378:metabolism*; D052216:Glucagon-Like Peptide 1; D000067757:Glucagon-Like Peptide-1 Receptor; D007150:Immunohistochemistry; D007328:Insulin / Q000378:metabolism; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008954:Models, Biological; D010446:Peptide Fragments / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D018027:Receptors, Glucagon / Q000032:analysis / Q000378:metabolism*; D013004:Somatostatin / Q000378:metabolism
C000593835:Glp1r protein, rat; D000067757:Glucagon-Like Peptide-1 Receptor; D007328:Insulin; D010446:Peptide Fragments; D011498:Protein Precursors; D018027:Receptors, Glucagon; D013004:Somatostatin; D052216:Glucagon-Like Peptide 1; D005934:Glucagon