Multiple Choice
Passage
Diabetic nephropathy (kidney disease) is characterized in part by a significant decrease in the glomerular filtration rate. Podocytes are differentiated cells that surround the glomerular capillaries and counteract the pressure of blood filtration. Hyperglycemia (elevated blood glucose) and capillary hypertension (high blood pressure) , both of which are common in diabetic patients, can subject podocytes to mechanical stress. This mechanical stress has been shown to regulate glucose uptake by podocytes, possibly by altering the production of glucose transport (GLUT) proteins.Researchers investigating GLUT2 and GLUT4 expression in rat podocytes measured the impact of mechanical stress on glucose uptake. Cells were grown for 4 hours on membranes exposed to atmospheric (atm) or high air pressure (HP) to mimic mechanical stress. Antibodies specific to GLUT2 and GLUT4 were used to visualize the expression of each under normal glucose (NG) and hyperglycemic (HG) conditions, and to assess the effect of mechanical stress on expression. The uptake of a radiolabeled glucose analogue, [3H]-2-deoxy-D-glucose (3H-2DG) , was then determined. The quantity of 3H-2DG transported by each GLUT protein was directly proportional to the cell surface expression.
![Passage Diabetic nephropathy (kidney disease) is characterized in part by a significant decrease in the glomerular filtration rate. Podocytes are differentiated cells that surround the glomerular capillaries and counteract the pressure of blood filtration. Hyperglycemia (elevated blood glucose) and capillary hypertension (high blood pressure) , both of which are common in diabetic patients, can subject podocytes to mechanical stress. This mechanical stress has been shown to regulate glucose uptake by podocytes, possibly by altering the production of glucose transport (GLUT) proteins.Researchers investigating GLUT2 and GLUT4 expression in rat podocytes measured the impact of mechanical stress on glucose uptake. Cells were grown for 4 hours on membranes exposed to atmospheric (atm) or high air pressure (HP) to mimic mechanical stress. Antibodies specific to GLUT2 and GLUT4 were used to visualize the expression of each under normal glucose (NG) and hyperglycemic (HG) conditions, and to assess the effect of mechanical stress on expression. The uptake of a radiolabeled glucose analogue, [<sup>3</sup>H]-2-deoxy-D-glucose (3H-2DG) , was then determined. The quantity of 3H-2DG transported by each GLUT protein was directly proportional to the cell surface expression. <strong>Figure 1</strong> Cell surface expression of GLUT transporters in response to mechanical stress and varying glucose concentration.In vivo studies have shown that transport via GLUT2 is noninducible and depends only on extracellular glucose concentrations. However, GLUT4-mediated uptake is induced by insulin binding and occurs under high glucose conditions when insulin is released. The standard K<sub>m</sub> values for GLUT2 and GLUT4 are 19.4 and 4.3 mM, respectively, at normal blood glucose levels after a meal (~7.8 mM) . The data shown in Figure 2 represent the combined kinetic properties of both transporters. <strong>Figure 2</strong> Plot of glucose uptake in podocytes with and without mechanical stress. Adapted from Lewko, B., Bryl, E., Witkowski, J. M., Latawiec, E., Angielski, S., & Stepinski, J. (2005) . Mechanical stress and glucose concentration modulate glucose transport in cultured rat podocytes. Nephrology Dialysis Transplantation, 20(2) , 306-311. -Which statement about glucose transport under physiological conditions is consistent with the kinetic data provided in the passage? A) GLUT2-mediated uptake is a first-order process. B) ATP is required for glucose uptake by both GLUT transporters. C) In the fed state, glucose concentration limits GLUT4-mediated uptake. D) Glucose transport is independent of the concentration gradient.](https://d2lvgg3v3hfg70.cloudfront.net/MD0008/11ecba2d_0e7c_899d_a3bf_e372713321b8_MD0008_00.jpg)
Figure 1 Cell surface expression of GLUT transporters in response to mechanical stress and varying glucose concentration.In vivo studies have shown that transport via GLUT2 is noninducible and depends only on extracellular glucose concentrations. However, GLUT4-mediated uptake is induced by insulin binding and occurs under high glucose conditions when insulin is released. The standard Km values for GLUT2 and GLUT4 are 19.4 and 4.3 mM, respectively, at normal blood glucose levels after a meal (~7.8 mM) . The data shown in Figure 2 represent the combined kinetic properties of both transporters.
![Passage Diabetic nephropathy (kidney disease) is characterized in part by a significant decrease in the glomerular filtration rate. Podocytes are differentiated cells that surround the glomerular capillaries and counteract the pressure of blood filtration. Hyperglycemia (elevated blood glucose) and capillary hypertension (high blood pressure) , both of which are common in diabetic patients, can subject podocytes to mechanical stress. This mechanical stress has been shown to regulate glucose uptake by podocytes, possibly by altering the production of glucose transport (GLUT) proteins.Researchers investigating GLUT2 and GLUT4 expression in rat podocytes measured the impact of mechanical stress on glucose uptake. Cells were grown for 4 hours on membranes exposed to atmospheric (atm) or high air pressure (HP) to mimic mechanical stress. Antibodies specific to GLUT2 and GLUT4 were used to visualize the expression of each under normal glucose (NG) and hyperglycemic (HG) conditions, and to assess the effect of mechanical stress on expression. The uptake of a radiolabeled glucose analogue, [<sup>3</sup>H]-2-deoxy-D-glucose (3H-2DG) , was then determined. The quantity of 3H-2DG transported by each GLUT protein was directly proportional to the cell surface expression. <strong>Figure 1</strong> Cell surface expression of GLUT transporters in response to mechanical stress and varying glucose concentration.In vivo studies have shown that transport via GLUT2 is noninducible and depends only on extracellular glucose concentrations. However, GLUT4-mediated uptake is induced by insulin binding and occurs under high glucose conditions when insulin is released. The standard K<sub>m</sub> values for GLUT2 and GLUT4 are 19.4 and 4.3 mM, respectively, at normal blood glucose levels after a meal (~7.8 mM) . The data shown in Figure 2 represent the combined kinetic properties of both transporters. <strong>Figure 2</strong> Plot of glucose uptake in podocytes with and without mechanical stress. Adapted from Lewko, B., Bryl, E., Witkowski, J. M., Latawiec, E., Angielski, S., & Stepinski, J. (2005) . Mechanical stress and glucose concentration modulate glucose transport in cultured rat podocytes. Nephrology Dialysis Transplantation, 20(2) , 306-311. -Which statement about glucose transport under physiological conditions is consistent with the kinetic data provided in the passage? A) GLUT2-mediated uptake is a first-order process. B) ATP is required for glucose uptake by both GLUT transporters. C) In the fed state, glucose concentration limits GLUT4-mediated uptake. D) Glucose transport is independent of the concentration gradient.](https://d2lvgg3v3hfg70.cloudfront.net/MD0008/11ecba2d_0e7c_b0ae_a3bf_6191410a37d4_MD0008_00.jpg)
Figure 2 Plot of glucose uptake in podocytes with and without mechanical stress.
Adapted from Lewko, B., Bryl, E., Witkowski, J. M., Latawiec, E., Angielski, S., & Stepinski, J. (2005) . Mechanical stress and glucose concentration modulate glucose transport in cultured rat podocytes. Nephrology Dialysis Transplantation, 20(2) , 306-311.
-Which statement about glucose transport under physiological conditions is consistent with the kinetic data provided in the passage?
A) GLUT2-mediated uptake is a first-order process.
B) ATP is required for glucose uptake by both GLUT transporters.
C) In the fed state, glucose concentration limits GLUT4-mediated uptake.
D) Glucose transport is independent of the concentration gradient.
Correct Answer:
Verified
Correct Answer:
Verified
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