Cortisol and IGF-1 synergistically up-regulate taurine transport by the rat skeletal muscle cell line, L6

This study was undertaken to evaluate effects of exercise-induced hormones, cortisol, IGF-1, and beta-endorphin, on the regulation of taurine transport activity in rat skeletal myoblasts, L6 cells. Challenge of L6 cells with cortisol (100 nM) for 24 hrs resulted in a 165% increase in taurine transport activity, 220% increase in V-max. of the taurine transporter, and 55% increase in taurine transporter/ beta-actin mRNA level compared with untreated control cells. Neither IGF-1 (1similar to100 nM) nor beta-endorphin (1similar to20 nM), added in the incubation medium separately for 24 Ins, affected taurine uptake by L6 cells. However, when cells were co-treated with 1GF-1 (10 nM) plus cortisol (100 nM), taurine transport activity (37% increase, p < 0.05), V-max of the transporter (54%, p < 0.05), and taurine transporter/beta-actin mRNA level were further increased compared to the value for cells treated with cortisol alone. These results suggest that taurine transport by skeletal muscle cells appear to be synergistically up-regulated during a prolonged exercise via elevated levels of cortisol and IGF-1 in muscle.