Sequence and expression of a constitutive, facilitated glucose transporter (GLUT1) in Atlantic cod Gadus morhua

A putative glucose transporter, GLUT1, is reported for Atlantic cod Gadus morhua. A combination of RT-PCR, RLM-RACE and genome walking were used to articulate a 4560 bp cDNA (GenBank accession number AY526497). It contains a 149 bp 5' UTR, a 1470 bp open reading frame and a 2941 bp 3' UTR. At the nucleotide level, the cod GLUT1 ORF shares 78.2% sequence identity to human GLUT1 and the deduced amino acid sequence clusters with GLUT1s from rainbow trout and carp. GLUT1 transcript is highly expressed in brain, gill, heart and kidney and expressed to a lower level in at least six other tissues. Expression is evident immediately upon fertilization of eggs. Six hours of hypoxia at 40% DO(2) did not alter expression levels in brain, gill, heart or kidney. The level of expression is not substantially altered in heart during low temperature challenge, although there is a suggestion that colder temperature could lead to lower levels of expression, consistent with the concept that the cold-acclimated heart has a reduced dependence upon glucose as a metabolic fuel. Two months of starvation did not significantly alter the level of expression of GLUT1 in heart. This is in marked contrast to the rat heart where fasting leads to a substantial decrease in GLUT1 levels. Overall, there is a ubiquitous tissue distribution of GLUT1, consistent with other species, and the level of gene expression, especially in heart, is relatively constant over a range of physiological conditions.