Modulation of hexose transport in cultured skeletal muscle

The modulation of hexose transport due to insulin and glucose starvation was investigated in cultures derived from the breast musculature of embryonic quail. Fused myotubes at 37°C exhibited a saturable, stereospecific basal uptake of both D-glucose and 3- O-methylglucose which was markedly inhibited by cytochalasin B, a potent inhibitor of hexose transport in other cell systems. In the presence of insulin, 3- O-methylglucose uptake was stimulated relative to untreated controls. Kinetic analysis indicated that insulin increased the V max of transport with no significant increase in the apparent K m. Incubation of myotubes in glucose-free medium for 24 h resulted in an increase in D-glucose and 3- O-methylglucose transport activity. Cycloheximide abolished this stimulation effect when it was included during the starvation period, but had no effect on transport in glucose-fed cells. Insulin binding studies on these myotubes indicate that high-affinity insulin receptors are present and continue to increase throughout the life of the culture. This high-affinity binding as well as the capacity to degrade insulin in these cells is characteristically similar to effects observed in other insulin-sensitive cell systems.