For past five years my undergraduate students and I have been interested how glucose is transported into cells and how that rate of transport rapidly adjusts as the cells' environment changes. Glucose is arguably the most important energy source in biological systems. Proper glucose uptake is critical to the maintenance and health of a wide variety of organisms. For example, in humans, diabetes is a disease in which glucose uptake is compromised either due to the insufficient production of insulin (type 1) or compromised response to insulin at peripheral tissues (type 2). The uptake of glucose across biological membranes is mediated by a family of proteins called GLUTs (GLUcose Transporters). Our lab is particularly interested in the regulation of two of these transporters-GLUT 4, which is responsive to insulin, and GLUT 1, which is found in a variety of tissues and is responsible for basal or background uptake. Acute regulation of GLUT 4 by agents such as insulin and exercise is primarily mediated by a translocation of the transporter from internal stores to the cell surface, thereby increasing glucose uptake. GLUT 1 was initially viewed to be responsible for basal uptake and therefore not acutely regulated by environmental conditions. However, recent data from our lab and others have indicated that cell stressors such as azide, hyperosmolarity, and methylene blue can quickly increase the transport of glucose through GLUT 1. Our current research focus is to understand the acute regulation of glucose uptake with a focus on the activity of GLUT 1. Our lab works with several cell types-intact mouse muscle (soleus and epitrochlearis), cultured fibroblast cells (L929, which contain only GLUT 1), and cultured myoblast cells and myotubes. Glucose uptake is measure by scintillation spectrometry using the radioactive glucose analog, 2-deoxyglucose or 3-O-methylglucose.

Current Projects

1. Effects of Methylene Blue: Methylene blue stimulates glucose uptake in L929 fibroblast cells in a dose dependant fashion (maximal effective concentration of 50 µM). A 5-9-fold increase in uptake occurs within 30 minutes. We are investigating the mechanism of this rapid activation of GLUT 1 by methylene blue.

Figure 1. Effects of MB on 2DG uptake. Cells were incubated at 37 °C for 45 minutes in low glucose DMEM buffer plus 5, 10, 25, 50, 75, or 100 µM MB as indicated. 10-minute 2DG uptakes were then measured. Data are means ± S.E. for three wells of a representative experiment. All conditions are statistically different from control at P<0.01 except 5 µM MB which was significant at P<0.05.

2. Effects of Glucose Starvation: Removal of glucose from the media for as little as 10 minutes stimulates glucose uptake in L929 fibroblast cells by over 10 fold. Unlike the effects of methylene blue, this effect is partially inhibited by wortmannin. We are investigating the effects of glucose starvation on the activation of glucose uptake.

3. Effects of Verapamil on basal and insulin-stimulated glucose uptake. Overdose of calcium channel blockers (CCB) such as verapamil results in a hyperglycemia. An effective rescue therapy for these patients is high doses of insulin. It appears that peripheral glucose uptake is compromised in the face of high doses of CCB's. In collaboration with Dr. Christopher Holstege at the University of Virginia , we are investigating the effects of verapamil on both basal and insulin-stimulated glucose uptake.

Figure 3. Effects of 150 µM verapamil on 2-DG uptake in the mouse soleus and epitrochlearus. Data represents the means ± s.e. for at least 13 samples. Both samples are statistically different (sol: P = 0.018; epi: P = 0.007) from basal conditions at P < 0.05.

4. Effects of Dietary Supplements: Type 2 diabetes and the pre-diabetic state known as Syndrome X are an increasing medical concern in this country. This has lead to an increasing market for nutrachemicals or dietary supplements marketed as effective aids for diabetes. We are interested in determining if these supplements have a measurable effect on glucose uptake in our cultured cells systems.