Glucose transport by human renal Na+/D-glucose cotransporters SGLT1 and SGLT2.
The human Na(+)/D-glucose cotransporter 2 (hSGLT2) is believed to be responsible for the bulk of glucose reabsorption in the kidney proximal convoluted tubule. Since blocking reabsorption increases urinary glucose excretion, hSGLT2 has become a novel drug target for Type 2 diabetes treatment. Glucose transport by hSGLT2 was studied at 37°C in human embryonic kidney 293T cells using whole cell patch-clamp electrophysiology. We compared hSGLT2 with hSGLT1, the transporter in the straight proximal tubule (S3 segment). hSGLT2 transports with surprisingly similar glucose affinity and lower concentrative power than hSGLT1: Na(+)/D-glucose cotransport by hSGLT2 was electrogenic with apparent glucose and Na(+) affinities of 5 and 25 mM, and a Na(+):glucose coupling ratio of 1; hSGLT1 affinities were 2 and 70 mM and coupling ratio of 2. Both proteins showed voltage-dependent steady-state transport; however, unlike hSGLT1, hSGLT2 did not exhibit detectable pre-steady-state currents in response to rapid jumps in membrane voltage. D-Galactose was transported by both proteins, but with very low affinity by hSGLT2 (≥100 vs. 6 mM). β-D-Glucopyranosides were either substrates or blockers. Phlorizin exhibited higher affinity with hSGLT2 (K(i) 11 vs. 140 nM) and a lower Off-rate (0.03 vs. 0.2 s⁻¹) compared with hSGLT1. These studies indicate that, in the early proximal tubule, hSGLT2 works at 50% capacity and becomes saturated only when glucose is ≥35 mM. Furthermore, results on hSGLT1 suggest it may play a significant role in the reabsorption of filtered glucose in the late proximal tubule. Our electrophysiological study provides groundwork for a molecular understanding of how hSGLT inhibitors affect renal glucose reabsorption.
Hummel
Charles S
CS
Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095-1751, USA.
Lu
Chuan
C
Loo
Donald D F
DD
Hirayama
Bruce A
BA
Voss
Andrew A
AA
Wright
Ernest M
EM
D000200:Action Potentials; D001693:Biological Transport, Active; D002247:Carbon Isotopes / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D005947:Glucose / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D007668:Kidney / Q000502:physiology*; D008757:Methylglucosides / Q000378:metabolism; D010695:Phlorhizin / Q000494:pharmacology; D051269:Sodium-Glucose Transporter 1 / Q000235:genetics / Q000378:metabolism*; D051297:Sodium-Glucose Transporter 2 / Q000235:genetics / Q000378:metabolism*; D013816:Thermodynamics
D002247:Carbon Isotopes; D008757:Methylglucosides; C495674:SLC5A1 protein, human; C089180:SLC5A2 protein, human; D051269:Sodium-Glucose Transporter 1; D051297:Sodium-Glucose Transporter 2; C027020:methylglucoside; D010695:Phlorhizin; D005947:Glucose