Isotonic transport by the Na+-glucose cotransporter SGLT1 from humans and rabbit.

T Zeuthen; A K Meinild; D D Loo; E M Wright; D A Klaerke

doi:10.1111/j.1469-7793.2001.0631h.x

Isotonic transport by the Na+-glucose cotransporter SGLT1 from humans and rabbit.

T Zeuthen, A K Meinild, D D Loo, E M Wright, D A Klaerke

75 Citations (Scopus)

Abstract

1. In order to study its role in steady state water transport, the Na+-glucose cotransporter (SGLT1) was expressed in Xenopus laevis oocytes; both the human and the rabbit clones were tested. The transport activity was monitored as a clamp current and the flux of water followed optically as the change in oocyte volume. 2. SGLT1 has two modes of water transport. First, it acts as a molecular water pump: for each 2 Na+ and 1 sugar molecule 264 water molecules were cotransported in the human SGLT1 (hSGLT1), 424 for the rabbit SGLT1 (rSGLT1). Second, it acts as a water channel. 3. The cotransport of water was tightly coupled to the sugar-induced clamp current. Instantaneous changes in clamp current induced by changes in clamp voltage were accompanied by instantaneous changes in the rate of water transport. 4. The cotransported solution was predicted to be hypertonic, and an osmotic gradient built up across the oocyte membrane with continued transport; this resulted in an additional osmotic influx of water. After 5-10 min a steady state was achieved in which the total influx was predicted to be isotonic with the intracellular solution. 5. With the given expression levels, the steady state water transport was divided about equally between cotransport, osmosis across the SGLT1 and osmosis across the native oocyte membrane. 6. Coexpression of AQP1 with the SGLT1 increased the water permeability more than 10-fold and steady state isotonic transport was achieved after less than 2 s of sugar activation. One-third of the water was cotransported, and the remainder was osmotically driven through the AQP1. 7. The data suggest that SGLT1 has three roles in isotonic water transport: it cotransports water directly, it supplies a passive pathway for osmotic water transport, and it generates an osmotic driving force that can be employed by other pathways, for example aquaporins.

Original language	English
Journal	Journal of Physiology
Volume	531
Issue number	3
Pages (from-to)	631-44
Number of pages	13
ISSN	0022-3751
DOIs	https://doi.org/10.1111/j.1469-7793.2001.0631h.x
Publication status	Published - 2001

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@article{033251f0bc8311dd8e02000ea68e967b,

title = "Isotonic transport by the Na+-glucose cotransporter SGLT1 from humans and rabbit.",

abstract = "1. In order to study its role in steady state water transport, the Na+-glucose cotransporter (SGLT1) was expressed in Xenopus laevis oocytes; both the human and the rabbit clones were tested. The transport activity was monitored as a clamp current and the flux of water followed optically as the change in oocyte volume. 2. SGLT1 has two modes of water transport. First, it acts as a molecular water pump: for each 2 Na+ and 1 sugar molecule 264 water molecules were cotransported in the human SGLT1 (hSGLT1), 424 for the rabbit SGLT1 (rSGLT1). Second, it acts as a water channel. 3. The cotransport of water was tightly coupled to the sugar-induced clamp current. Instantaneous changes in clamp current induced by changes in clamp voltage were accompanied by instantaneous changes in the rate of water transport. 4. The cotransported solution was predicted to be hypertonic, and an osmotic gradient built up across the oocyte membrane with continued transport; this resulted in an additional osmotic influx of water. After 5-10 min a steady state was achieved in which the total influx was predicted to be isotonic with the intracellular solution. 5. With the given expression levels, the steady state water transport was divided about equally between cotransport, osmosis across the SGLT1 and osmosis across the native oocyte membrane. 6. Coexpression of AQP1 with the SGLT1 increased the water permeability more than 10-fold and steady state isotonic transport was achieved after less than 2 s of sugar activation. One-third of the water was cotransported, and the remainder was osmotically driven through the AQP1. 7. The data suggest that SGLT1 has three roles in isotonic water transport: it cotransports water directly, it supplies a passive pathway for osmotic water transport, and it generates an osmotic driving force that can be employed by other pathways, for example aquaporins.",

author = "T Zeuthen and Meinild, {A K} and Loo, {D D} and Wright, {E M} and Klaerke, {D A}",

note = "Keywords: Animals; Aquaporin 1; Aquaporins; Biological Transport; Blood Group Antigens; Homeostasis; Humans; Hypertonic Solutions; Isotonic Solutions; Membrane Glycoproteins; Monosaccharide Transport Proteins; Oocytes; Osmosis; Patch-Clamp Techniques; Permeability; Rabbits; Sodium-Glucose Transporter 1; Water; Xenopus laevis",

year = "2001",

doi = "10.1111/j.1469-7793.2001.0631h.x",

language = "English",

volume = "531",

pages = "631--44",

journal = "Journal of Physiology",

issn = "0022-3751",

publisher = "Wiley-Blackwell",

number = "3",

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TY - JOUR

T1 - Isotonic transport by the Na+-glucose cotransporter SGLT1 from humans and rabbit.

AU - Zeuthen, T

AU - Meinild, A K

AU - Loo, D D

AU - Wright, E M

AU - Klaerke, D A

N1 - Keywords: Animals; Aquaporin 1; Aquaporins; Biological Transport; Blood Group Antigens; Homeostasis; Humans; Hypertonic Solutions; Isotonic Solutions; Membrane Glycoproteins; Monosaccharide Transport Proteins; Oocytes; Osmosis; Patch-Clamp Techniques; Permeability; Rabbits; Sodium-Glucose Transporter 1; Water; Xenopus laevis

PY - 2001

Y1 - 2001

N2 - 1. In order to study its role in steady state water transport, the Na+-glucose cotransporter (SGLT1) was expressed in Xenopus laevis oocytes; both the human and the rabbit clones were tested. The transport activity was monitored as a clamp current and the flux of water followed optically as the change in oocyte volume. 2. SGLT1 has two modes of water transport. First, it acts as a molecular water pump: for each 2 Na+ and 1 sugar molecule 264 water molecules were cotransported in the human SGLT1 (hSGLT1), 424 for the rabbit SGLT1 (rSGLT1). Second, it acts as a water channel. 3. The cotransport of water was tightly coupled to the sugar-induced clamp current. Instantaneous changes in clamp current induced by changes in clamp voltage were accompanied by instantaneous changes in the rate of water transport. 4. The cotransported solution was predicted to be hypertonic, and an osmotic gradient built up across the oocyte membrane with continued transport; this resulted in an additional osmotic influx of water. After 5-10 min a steady state was achieved in which the total influx was predicted to be isotonic with the intracellular solution. 5. With the given expression levels, the steady state water transport was divided about equally between cotransport, osmosis across the SGLT1 and osmosis across the native oocyte membrane. 6. Coexpression of AQP1 with the SGLT1 increased the water permeability more than 10-fold and steady state isotonic transport was achieved after less than 2 s of sugar activation. One-third of the water was cotransported, and the remainder was osmotically driven through the AQP1. 7. The data suggest that SGLT1 has three roles in isotonic water transport: it cotransports water directly, it supplies a passive pathway for osmotic water transport, and it generates an osmotic driving force that can be employed by other pathways, for example aquaporins.

AB - 1. In order to study its role in steady state water transport, the Na+-glucose cotransporter (SGLT1) was expressed in Xenopus laevis oocytes; both the human and the rabbit clones were tested. The transport activity was monitored as a clamp current and the flux of water followed optically as the change in oocyte volume. 2. SGLT1 has two modes of water transport. First, it acts as a molecular water pump: for each 2 Na+ and 1 sugar molecule 264 water molecules were cotransported in the human SGLT1 (hSGLT1), 424 for the rabbit SGLT1 (rSGLT1). Second, it acts as a water channel. 3. The cotransport of water was tightly coupled to the sugar-induced clamp current. Instantaneous changes in clamp current induced by changes in clamp voltage were accompanied by instantaneous changes in the rate of water transport. 4. The cotransported solution was predicted to be hypertonic, and an osmotic gradient built up across the oocyte membrane with continued transport; this resulted in an additional osmotic influx of water. After 5-10 min a steady state was achieved in which the total influx was predicted to be isotonic with the intracellular solution. 5. With the given expression levels, the steady state water transport was divided about equally between cotransport, osmosis across the SGLT1 and osmosis across the native oocyte membrane. 6. Coexpression of AQP1 with the SGLT1 increased the water permeability more than 10-fold and steady state isotonic transport was achieved after less than 2 s of sugar activation. One-third of the water was cotransported, and the remainder was osmotically driven through the AQP1. 7. The data suggest that SGLT1 has three roles in isotonic water transport: it cotransports water directly, it supplies a passive pathway for osmotic water transport, and it generates an osmotic driving force that can be employed by other pathways, for example aquaporins.

U2 - 10.1111/j.1469-7793.2001.0631h.x

DO - 10.1111/j.1469-7793.2001.0631h.x

M3 - Journal article

C2 - 11251046

SN - 0022-3751

VL - 531

SP - 631

EP - 644

JO - Journal of Physiology

JF - Journal of Physiology

IS - 3

ER -

Isotonic transport by the Na+-glucose cotransporter SGLT1 from humans and rabbit.

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