Effects of temperature on basal and insulin-stimulated glucose transport activities in fat cells. Further support for the translocation hypothesis of insulin action.

O Ezaki,T Kono

doi:10.1016/s0021-9258(19)45381-7

Abstract

Effects of temperature on glucose transport in fat cells were studied. In this system, the basal (no insulin) glucose transport activity was higher at approximately 25-30 degrees C than at 37 degrees C, as previously reported (Vega, F. V., and Kono, T. (1979) Arch. Biochem. Biophys. 192, 120-127). The stimulatory effect of low temperature (or the insulin-like effect) was reversible and apparently required metabolic energy for both its forward and reverse reactions. By lowering the ATP level with 2,4-dinitrophenol, one could separately determine the insulin-like stimulatory effect of low temperature and its inhibitory effect on the transport process itself. The maximum level of stimulation by low temperature was greater at 10 degrees C than at 25-30 degrees C, but the rate of stimulation was considerably slower at 10 degrees C than at 25-30 degrees C. When cells were exposed to low temperature, the glucose transport activity in the plasma membrane-rich fraction was increased, while that in the Golgi-rich fraction was decreased. The Arrhenius plot of the basal glucose transport activity determined in the presence of dinitrophenol was apparently linear from 10 to 37 degrees C and parallel to that of the plus insulin activity measured either in the presence or absence of dinitrophenyl. Insulin itself slowly stimulated the glucose transport activity at 10 degrees C. These results are consistent with the view that (a) low temperature, like insulin, induces translocation of the glucose transport activity from an intracellular storage site to the plasma membrane, (b) insulin stimulates glucose transport activity without changing its activation energy, and (c) subcellular membranes do not entirely stop their movement at a low temperature, e.g, at 10 degrees C.

Highlights

Effects of temperature on glucose transport in fat Finch (10) that the glucose transport activities in the basal cells were studied.In thissystem, the basal and plus insulin forms of fat cells show different responses to glucose transport activity was higher at approximateclhyanges in the incubation temperature
30 "C.When cells were exposetdo low temperature, the glucose transport activity in the plasma membranerich fraction was increasewdh, ile that in theGolgi-rich insulin) glucose transport activity is higher at 25 "C than at 37 "C (7). Because of this latter observation, we suggested earlier that translocationof the transport activitymay not be the only mechanism by which insulinstimulates glucose transport in fat cells (1,2)
We glucose transport activity determined in the presence approached this problem with the working hypothesis that of dinitrophenol was apparently linear fro1m0 to 37 "C low temperature has aninsulin-like activity

Summary

Osamu Ezaki and Tetsuro Konot

From the Departmentof Physiology, School of Medicine, Vanderbilt University, Nashville, Tennessee 37232. 30 "C.When cells were exposetdo low temperature, the glucose transport activity in the plasma membranerich fraction was increasewdh, ile that in theGolgi-rich insulin) glucose transport activity is higher at 25 "C than at 37 "C (7). The above temperature data were apparently in agreement with an alternat,e hypothesis, such as thatproposed by Amatruda and Finch(10) and Pilch et al (11) who suggested that insulin might stimulate glucose transport in fat cells by increasingfluidity of the plasma membrane. The glucose transport activity of fat cells was assessed from the rate of uptake of 3-O-methyl-~-['~C]glucose(1mM) The uptake of this sugarisomer wasroutinely determinedby the oil flotation method of Gliemann et al (17) as specified by Vega and Kono (7);the time for incubation of cells with the labeled sugar was 10 or 60 s. Since we the other hand, it wparseviously reported by Vega and Kono were concerned about theeffects of temperature, all the solutions and containers that would come in contact with the incubation mixture (7), Czech (8),Whitesell and Gliemann (9),and Amatruda and were carefullyequilibrated with the proper temperatures priotro use

Theresults of thetransportassayarereported in terms of the

RESULTS

TRANSPORT ASSAY

The reason for this is not clear although several possibilities