Researchers are investigating the relationship between glucose transport proteins and insulin concentration in different types of tissues. Experiments in which cells are taken from various tissue samples and exposed to increasing concentrations of insulin are performed. The number of surface glucose transporters are then measured. The results from 2 cell samples are plotted on the graphs below. Which of the following cell types are most likely represented in cell samples A and B, respectively?

Question

Researchers are investigating the relationship between glucose transport proteins and insulin concentration in different types of tissues. Experiments in which cells are taken from various tissue samples and exposed to increasing concentrations of insulin are performed. The number of surface glucose transporters are then measured. The results from 2 cell samples are plotted on the graphs below.

Which of the following cell types are most likely represented in cell samples A and B, respectively?

Quizplus · Accepted Answer

11ec160b_36c6_9d8e_9249_d5402cbe5afa_MD0001_00 The glucose transport proteins (GLUTs) are a family of transmembrane proteins responsible for transport of glucose across cell membranes. Of these, only GLUT-4 is responsive to insulin. In the absence of insulin, GLUT-4 is sequestered in the cytoplasm and the cells become less permeable to glucose. However, increasing insulin concentrations induce translocation of GLUT-4 to the plasma membrane, facilitating glucose transport into the cell (sample B). GLUT-4 is predominantly expressed in skeletal muscle cells and adipocytes, where it facilitates insulin-mediated glucose uptake and storage. In contrast to GLUT-4, GLUTs 1, 2, 3, and 5 are always present on the plasma membrane, regardless of insulin levels, and are responsible for insulin-independent glucose transport (sample A). (Choices A, B, and C) Glucose uptake by hepatocytes, pancreatic beta cells, neurons, and enterocytes primarily involves insulin-independent glucose transporters and does not substantially change with insulin concentration. (Choice E) Both skeletal myocytes and adipocytes express GLUT-4 and would show increased glucose uptake in response to insulin. Educational objective: Glucose transport protein (GLUT)-4 is an insulin-sensitive glucose transporter expressed in skeletal muscle cells and adipocytes that translocates to the plasma membrane in response to increasing insulin levels. In contrast, GLUT-1, 2, 3, and 5 are always present on the plasma membrane and constitutively transport glucose in an insulin-independent manner. __________ References: Cellular regulation of glucose uptake by glucose transporter GLUT4. (http://www.ncbi.nlm.nih.gov/pubmed/25344989)

Researchers Are Investigating the Relationship Between Glucose Transport Proteins and Insulin