Absence of evidence of translocation of GLUT2 to the apical membrane of enterocytes in everted intestinal sleeves.
BACKGROUND
Traditional models of intestinal glucose absorption confine GLUT2 to the basolateral membrane. Evidence suggests that GLUT2 is translocated to the apical membrane when the enterocyte is exposed to high luminal glucose concentrations.


OBJECTIVE
GLUT2 translocates to the apical membrane by a PKC signaling mechanism dependent on activity of SGLT1 and the cellular cytostructure.


METHODS
Transporter-mediated glucose uptake was studied in rat jejunum using everted sleeves under seven conditions: Control, SGLT1 inhibition (phlorizin), GLUT2 inhibition (phloretin), both SGLT1 and GLUT2 inhibition, PKC inhibition (calphostin C or chelerythrine), and disruption of cellular cytostructure (nocodazole). Each condition was tested in iso-osmotic solutions of 1, 20, or 50 mM glucose for 1 or 5 min incubations (n = 6 rats each).


RESULTS
Control rats exhibited a saturable pattern of uptake at both durations of incubation. Phlorizin (P ≤ 0.006 each) inhibited markedly and phloretin (P ≤ 0.01 each) inhibited partially glucose uptake in all concentrations and time. Phloretin and phlorizin together completely inhibited uptake (P = 0.004 each). Calphostin C, chelerythrine, and nocodazole had little effect on glucose uptake at either 1 or 5 min. Inhibition of SGLT1 led to near complete cessation of transporter-mediated glucose uptake, while GLUT2 inhibition led to partial inhibition, suggesting some constitutive expression of GLUT2 in the apical membrane. Disruption of PKC signaling or cytoskeletal integrity partially inhibited transporter-mediated glucose uptake only in 1 mM glucose, suggesting a non-specific effect.


CONCLUSIONS
Under these conditions, it does not appear that GLUT2 is translocated to the apical membrane on the cellular cytostructure in response to PKC signaling.
Scow
Jeffrey S
JS
Mayo Clinic Department of Surgery, Rochester, Minnesota 55905, USA.
Iqbal
Corey W
CW
Jones
Thomas W
TW
Qandeel
Hisham G
HG
Zheng
Ye
Y
Duenes
Judith A
JA
Nagao
Munenori
M
Madhavan
Srivats
S
Sarr
Michael G
MG
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism*; D003599:Cytoskeleton / Q000502:physiology; D020895:Enterocytes / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D051273:Glucose Transporter Type 2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007583:Jejunum / Q000166:cytology / Q000378:metabolism*; D023421:Models, Animal; D010693:Phloretin / Q000494:pharmacology; D010695:Phlorhizin / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D011917:Rats, Inbred Lew; D015398:Signal Transduction / Q000502:physiology*; D051269:Sodium-Glucose Transporter 1 / Q000037:antagonists & inhibitors / Q000378:metabolism
D051273:Glucose Transporter Type 2; C495683:Slc2a2 protein, rat; C495676:Slc5a1 protein, rat; D051269:Sodium-Glucose Transporter 1; D010695:Phlorhizin; D011493:Protein Kinase C; D005947:Glucose; D010693:Phloretin