Biochemical localisation of the 5-HT2A (serotonin) receptor in rat skeletal muscle

The 5-HT2A receptor was recently shown to localise morphologically to the transverse tubules (TT) in rat foetal myoblasts. Receptor activation enhanced the expression of genes involved in myogenesis, and its TT localisation has led to the suggestion that it may participate in excitation-contraction coupling. In order to gain further insights into 5-HT2A receptor function in muscle we have (i) investigated its biochemical localisation in adult rat skeletal muscle and (ii) determined whether receptor expression is dependent upon muscle type. Immunoblot analysis of muscle membranes, isolated by subcellular fractionation, revealed that adult muscle expresses the 5-HT2A receptor and that it resides exclusively in plasma membranes and not in TT. No differences in 5-HT2A abundance were observed between red and white muscle, suggesting that receptor expression does not correlate with the metabolic or contractile properties of the muscle fibre. Our data indicate that 5-HT2A expression in skeletal muscle is maintained into adulthood and that its absence from TT make it an unlikely participant in the excitation-contraction coupling process.