Glucagon-like peptide 1 receptor expression in primary porcine proximal tubular cells.
BACKGROUND
GLP-1 is secreted into the circulation after food intake. The main biological effects of GLP-1 include stimulation of glucose dependent insulin secretion and induction of satiety feelings. Recently, it was demonstrated in rats and humans that GLP-1 can stimulate renal excretion of sodium. Based on these data, the existence of a renal GLP-1 receptor (GLP-1R) was postulated. However, the exact localization of the GLP-1R and the mechanism of this GLP-1 action have not yet been investigated.


METHODS
Primary porcine proximal tubular cells were isolated from porcine kidneys. Expression of GLP-1R was measured at the mRNA level by quantitative RT-PCR. Protein expression of GLP-1R was verified with immunocytochemistry, immunohistochemistry and Western blot analysis. Functional studies included transport assessments of sodium and glucose using three different GLP-1 concentrations (200 pM, 2 nM and 20 nM), 200 pM exendin-4 (GLP-1 analogue) and an inhibitor of the dipeptidylpeptidase IV (DPPIV) enzyme (P32/98 at 10 microM). Finally, the expression of NHE3, the predominant Na(+)/H(+) exchanger in proximal tubular cells, was also investigated.


RESULTS
GLP-1R, NHE3 and DPPIV were expressed at the mRNA level in porcine proximal tubular kidney cells. GLP-1R expression was confirmed at the protein level. Staining of human and pig kidney cortex revealed that GLP-1R was predominantly expressed in proximal tubular cells. Functional assays demonstrated an inhibition of sodium re-absorption with GLP-1 after 3 h of incubation. Exendin-4 and GLP-1 in combination with P32/98 co-administration had no clear influence on glucose and sodium uptake and transport.


CONCLUSIONS
GLP-1R is functionally expressed in porcine proximal tubular kidney cells. Addition of GLP-1 to these cells resulted in a reduced sodium re-absorption. GLP-1 had no effect on glucose re-absorption. We conclude that GLP-1 modulates sodium homeostasis in the kidney most likely through a direct action via its GLP-1R in proximal tubular cells.
Schlatter
P
P
Department of Clinical Pharmacology and Toxicology, University Hospital of Basel, Hebelstr. 2, CH-4031 Basel, Switzerland.
Beglinger
C
C
Drewe
J
J
Gutmann
H
H
D000818:Animals; D015153:Blotting, Western; D018929:Cell Culture Techniques; D002478:Cells, Cultured; D054873:Dipeptidyl-Peptidase IV Inhibitors; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000077270:Exenatide; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism / Q000494:pharmacology; D000067757:Glucagon-Like Peptide-1 Receptor; D005947:Glucose / Q000032:analysis / Q000378:metabolism; D007150:Immunohistochemistry; D007687:Kidney Tubules, Proximal / Q000166:cytology* / Q000378:metabolism*; D007700:Kinetics; D010421:Pentanoic Acids / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D018027:Receptors, Glucagon / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012964:Sodium / Q000037:antagonists & inhibitors / Q000378:metabolism; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D013552:Swine; D053778:Thiazolidines / Q000494:pharmacology; D014688:Venoms / Q000494:pharmacology
D054873:Dipeptidyl-Peptidase IV Inhibitors; D004791:Enzyme Inhibitors; C000593833:GLP1R protein, human; C000593835:Glp1r protein, rat; D000067757:Glucagon-Like Peptide-1 Receptor; C453900:P32-98 compound; D010421:Pentanoic Acids; D010455:Peptides; D012333:RNA, Messenger; D018027:Receptors, Glucagon; C000613385:SLC9A3 protein, human; C000613387:Slc9a3 protein, rat; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D053778:Thiazolidines; D014688:Venoms; D052216:Glucagon-Like Peptide 1; D012964:Sodium; D000077270:Exenatide; D005947:Glucose