You are studying the responses of myocytes in culture following their exposure to γ-irradiation. In a comparison to normal myocytes you find that when insulin is added, the normal cells actively take up glucose but the irradiated cells do not. Binding studies show that both cell populations bind the same amount of insulin with the same dissociation kinetics, indicating the receptors on the irradiated cells are unchanged. Given these results, which of the following proteins is most likely to be defective in the irradiated cells? A) a G_q-type G-protein B) a G_s-type G-protein C) phosphatidic acid phosphatase D) phosphatidylinositol-3-kinase (PI3K) E) protein kinase A (PKA)

Question

Quizplus · Accepted Answer

The Answer is D
EXPLANATION: In most nonhepatic tissues, insulin increases glucose uptake by increasing the number of plasma membrane glucose transporters, specifically GLUT4 in muscle cells. Insulin action leads to an increase in the activity of PI3K, which in turn phosphorylates membrane phospholipids generating phosphatidylinositol-3,4,5-trisphophate (PIP₃) from phosphatidylinositol-4,5-bisphosphate (PIP₂). PIP3 then activates the kinase PDK1, which in turn phosphorylates and activates a protein kinase C isoform (PKC-ζ) involved in the mobilization of GLUT4 to the plasma membrane. Loss of PI3K activation or activity would, therefore, result in reduced capacity to mobilize GLUT4-containing vesicles to the membrane.

You Are Studying the Responses of Myocytes in Culture Following