Analyze the Data Chapter 4: FACS of Glucose Transport In unstimulated muscle cel
ID: 196336 • Letter: A
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Analyze the Data Chapter 4: FACS of Glucose Transport
In unstimulated muscle cells, the glucose transporter Glut4 is present in the membrane of endosomes. Upon stimulation of these cells with insulin, the endosomes fuse with the plasma membrane, thereby depositing Glut4 in the plasma membrane, where it serves to transport glucose into the cells (see Figure 15-34 on page 659). In order for insulin to elicit this change in Glut4 localization, insulin must bind to its receptor, present in the plasma membrane of some cells. To determine if a stem cell line can be induced in culture to differentiate into muscle cells in which Glut4 is expressed and exhibits this insulin-dependent change in behavior, the following studies were undertaken.
A stem cell line was incubated under culture conditions in which stem cells can differentiate into various specific cell types. The cells were then incubated in the presence and absence of insulin. To determine if either Glut4 or the insulin receptor were present on the cell surface of cells within this population, antibodies that specifically recognize each protein were used to label the cells. Glut4 on the cell surface was detected by an anti-Glut4 antibody, which fluoresces green; the insulin receptor on the cell surface was detected by an anti-insulin receptor antibody, which fluoresces red. These cells were then placed in a fluorescence activated cell sorter FACS machine (see Figure 9-29 in the text) and sorted based on both red and green fluorescence. The following data were obtained. Each • on the graphs represents 20 cells. An increased value of fluorescence intensity indicates that more antibody has bound to those cells.
Do all cells in the population express insulin receptor on their surface? Is this expression
dependent on the presence of insulin? Explain.
(a) Insulin 10 104 10 b) Insulin 107 104 100 104 107 10° 104 10 Red fluorescence Red fluorescence.Explanation / Answer
From graph a, we conclude the presence of insulin receptors, because red fluorescence is because of binding of anti-insulin antibodies. from the graph b, for insulin +, we see that green fluorescence is present, that means the anti glut 4 antibodies has bound to glut 4. This means that insulin is causing the glut 4 proteins to be expressed on the surface. This as per above understanding is possible when there are insulin receptors on the surface, as it is insulin which causes glut 4 to reach the membrane and localize glucose inside the cells so the expression is insulin dependent. So, yes cells express insulin receptor on their surface and the expression of glut 4 is insulin dependent.
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