WBR0936: Difference between revisions
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|SubCategory=Endocrine, Musculoskeletal/Rheumatology | |SubCategory=Endocrine, Musculoskeletal/Rheumatology | ||
|Prompt=A scientist is studying the mechanism of exercise-induced insulin sensitivity in diabetic patients. A biopsy of the vastus lateralis muscle is obtained from the left leg at rest. 3-6 weeks later, the subjects performed 45-60 minutes of cycling at 70% VO2 max, and immediately thereafter a biopsy was obtained from the right vastus lateralis muscle. The investigator performs immunohistochemistry of the obtained tissues. Which of the following will demonstrate increased localization to the plasma membrane? | |Prompt=A scientist is studying the mechanism of exercise-induced insulin sensitivity in diabetic patients. A biopsy of the vastus lateralis muscle is obtained from the left leg at rest. 3-6 weeks later, the subjects performed 45-60 minutes of cycling at 70% VO2 max, and immediately thereafter a biopsy was obtained from the right vastus lateralis muscle. The investigator performs immunohistochemistry of the obtained tissues. Which of the following will demonstrate increased localization to the plasma membrane? | ||
|Explanation= | |Explanation=Glucose is a charged molecule that requires transporters to enter cells. The glucose transporters found in various cell types in the body are differentially expressed and regulate glucose uptake differently. GLUT4 is the insulin responsive glucose transporter. It is expressed in muscle and adipose tissue, and its cell-surface expression can be increased by exercise. | ||
{| class="wikitable" | |||
| '''Name''' || '''Distribution''' || '''Notes''' | |||
|- | |||
| [[GLUT1]] || Is widely distributed in [[fetus|fetal]] tissues. In the adult, it is expressed at highest levels in [[erythrocytes]] and also in the endothelial cells of barrier tissues such as the [[blood–brain barrier]]. However, it is responsible for the low-level of basal glucose uptake required to sustain respiration in all cells. || Levels in cell membranes are increased by reduced glucose levels and decreased by increased glucose levels. | |||
|- | |||
| [[GLUT2]] || Is a bidirectional transporter, allowing glucose to flow in 2 directions. Is expressed by [[renal tubular]] cells, small intestinal epithelial cells, [[liver]] cells and pancreatic [[beta cells]]. It is also present in the basolateral membrane of the small intestine epithelium. Bidirectionality is required in liver cells to uptake glucose for glycolysis, and release of glucose during gluconeogenesis. In pancreatic beta cells, free flowing glucose is required so that the intracellular environment of these cells can accurately gauge the serum glucose levels. All three monosaccharides ([[glucose]], [[galactose]] and [[fructose]]) are transported from the intestinal mucosal cell into the portal circulation by GLUT2|| Is a high-capacity and low-affinity isoform. There is some evidence{{fact|date=March 2013}} that GLUT 1 and 3 are actually the functional transporters in beta cells. | |||
|- | |||
| [[GLUT3]]|| Expressed mostly in [[neuron]]s (where it is believed to be the main glucose transporter isoform), and in the [[placenta]]. || Is a high-affinity isoform, allowing it to transport even in times of low glucose concentrations. | |||
|- | |||
| [[GLUT4]] || Found in [[adipose tissue]]s and [[striated muscle]] ([[skeletal muscle]] and [[cardiac muscle]]). || Is the [[insulin]]-regulated glucose transporter. Responsible for insulin-regulated glucose storage. | |||
|} | |||
Educational objective: GLUT4 is an insulin-responsive glucose transporter found in adipose tissue and muscle that translocates to the cell membrane upon exercise. | Educational objective: GLUT4 is an insulin-responsive glucose transporter found in adipose tissue and muscle that translocates to the cell membrane upon exercise. | ||
Revision as of 04:19, 12 December 2013
| Author | PageAuthor::William J Gibson |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry |
| Sub Category | SubCategory::Endocrine, SubCategory::Musculoskeletal/Rheumatology |
| Prompt | [[Prompt::A scientist is studying the mechanism of exercise-induced insulin sensitivity in diabetic patients. A biopsy of the vastus lateralis muscle is obtained from the left leg at rest. 3-6 weeks later, the subjects performed 45-60 minutes of cycling at 70% VO2 max, and immediately thereafter a biopsy was obtained from the right vastus lateralis muscle. The investigator performs immunohistochemistry of the obtained tissues. Which of the following will demonstrate increased localization to the plasma membrane?]] |
| Answer A | AnswerA::GLUT1 |
| Answer A Explanation | AnswerAExp::Incorrect: GLUT1 is expressed in erythrocytes and the brain. It does not translocate to the cell membrane with exercise. |
| Answer B | AnswerB::GLUT2 |
| Answer B Explanation | AnswerBExp::Incorrect: GLUT2 is a bidirectional glucose transporter that is expressed in pancreatic islet cells, the liver and the kidney. It does not translocate to the cell membrane with exercise. |
| Answer C | AnswerC::GLUT3 |
| Answer C Explanation | AnswerCExp::Incorrect: GLUT3 is primarily expressed in neurons and does not translocate to the cell membrane with exercise. |
| Answer D | AnswerD::GLUT4 |
| Answer D Explanation | AnswerDExp::Correct: GLUT4 is an insulin-responsive glucose transporter found in adipose tissue and muscle that translocates to the cell membrane upon exercise. |
| Answer E | AnswerE::GLUT5 |
| Answer E Explanation | AnswerEExp::Incorrect: GLUT5 is a fructose transporter expressed on the apical border of enterocytes in the small intestine. It does not translocate to the cell membrane with exercise. |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::Glucose is a charged molecule that requires transporters to enter cells. The glucose transporters found in various cell types in the body are differentially expressed and regulate glucose uptake differently. GLUT4 is the insulin responsive glucose transporter. It is expressed in muscle and adipose tissue, and its cell-surface expression can be increased by exercise.
{ |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Muscle, WBRKeyword::Insulin, WBRKeyword::Glucose, WBRKeyword::Receptor, WBRKeyword::Exercise, WBRKeyword::Transporter |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |