We have found a complex alteration in the expression of the glucose transporter protein and mRNA in developing rat brain tissue. Before birth (gestational days 19- 20), the rat brain glucose transporter was comprised of a diffuse protein doublet of approximately 43,000 and 50,000 mol wt (Mr) by Western blot analysis. Immediately after birth (1-2 days), the total amount of immunoreactive glucose transporter decreased approximately 5-fold, primarily due to a loss of the higher (50,000) Mr component with a relatively smaller decrease in the 43,000 Mr band. Subsequently, the amount of the 43,000 Mr band progressively increased from days 5 to 60 and the 50,000 Mr band increased from days 15 to 60. By 60 days postdelivery, the relative amounts of the glucose transporter protein were similar to those on the 19th gestational day. N-Glycanase treatment of the developing rat brain membranes demonstrated that the regulation of the two different Mr weight glucose transporter species occurred as a result of differential glycosylation. In contrast to the Western blot analysis, [3H] cytochalasin-B binding studies demonstrated no significant developmental alteration in the total amount of glucose transporter protein in rat brain tissue. However, consistent with the Western blots, Northern blot analysis using rat brain transporter cDNA revealed a dramatic decrease in the content of the glucose transporter mRNA immediately subsequent to birth, followed by a gradual increase back to the prenatal levels. These data suggest that the rat brain-type glucose transporter is developmentally regulated, but may be associated with the compensatory expression of another unidentified glucose transporter protein in newborn rats.
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