Insulin-Dependent Apparent Translocation of Glucose Transport Activity: Studies by the Reconstitution Method
Nearly a decade ago, we found that when rat epididymal adipocytes were exposed to [125I]iodoinsulin for 10 min at 37°C, 125I activity would associate with two subcellular structures that could be fractionated by sucrose density-gradient centrifugation into the plasma membrane fraction (peak 1) and a low-density microsomal fraction (peak 2).(1) The latter peak (peak 2 of 125I activity) was later identified as the peak of the internalized hormone.(2,3) During this study, however, we noticed several similarities between the characteristics of the peak 2 formation, i,e., the endocytotic internalization of the hormone-receptor complex, and those of the hormonal action on glucose transport. Thus, both reactions are very slow at a low temperature, such as 15°C,(2) both reactions require adenosine triphosphate (ATP) not only for their development(2,3) but also for their reversal,(4,5) and both reactions are completed in approximately 5–10 min at 37°C when the hormone concentration is 1 nM.(2,6) We therefore postulated as a working hypothesis that the complex of glucose and its transport carrier might be co-internalized along with the insulin-receptor complex. In theory, one can test this working hypothesis by measuring the distribution of glucose transport activity in subcellular fractions obtained from the basal and plus-insulin states of adipocytes using the aforementioned sucrose density-gradient centrifugation.
KeywordsSubcellular Fraction Insulinlike Effect Glucose Transport Activity States Public Health Service Grant Basal Glucose Transport
Unable to display preview. Download preview PDF.
- 4.Kono, T., Vega, F.V., Raines, K.B., and Shumway, S.J., 1977, Fed. Proc. 36: 341.Google Scholar
- 19.Kono, T., 1982, in Membranes and Transport (A.N. Martonosi, ed.), Vol. 2, pp. 551–554, Plenum, New York.Google Scholar
- 35.Lamer, J., Cheng, K., Schwartz, C., Kikuchi, K., Tamura, S., Creacy, S., Dubler, R., Galasko, G., Pullin, C., and Katz, M., 1982 Recent Prog. Horm. Res. 38: 511–556.Google Scholar
- 41.Gorga, J.C., and Lienhard, G.E., 1982, Fed. Proc. 41: 627.Google Scholar