GLUT-4 expression is not consistently higher in type-1 than in type-2 fibres of rat and human vastus lateralis muscles; an immunohistochemical study

In whole muscle homogenates, the glucose transporter-4 (GLUT-4) content is reported to be higher in muscles consisting predominantly of oxidative (typ e-1) muscle fibres than in muscles consisting predominantly of glycolytic ( type-2) fibres. From these findings, it has been deduced that in rat muscle , oxidative fibres have an intrinsically higher level of GLUT-4 protein tha n glycolytic fibres. No data is available concerning human muscle. Moreover , the fibre-type-specific expression of GLUT-4 has not yet been examined di rectly. In this study, the relative abundance of GLUT-4 protein expression in individual fibres of different types within a muscle was compared direct ly in irnmunohistochemical assays. The human vastus lateralis muscle and a selection of rat muscles were studied using a novel GLUT-4 anti-serum. It i s concluded that the pattern of fibre-type-specific GLUT-4 expression diffe rs between human and rats and varies between the different muscles studied, indicating that non-fibre-type-specific factor(s) affect expression of GLU T-4. The observation that within a muscle a fibre-type-specific expression of GLUT-4 was observed indicates that fibre-type-specific factors contribut e to GLUT-4 expression as well. Thus, it can be postulated that both fibre- type-dependent and fibre-type-independent factors affect GLUT-4 expression.