A transient increase in amino acid transport modulated by insulin in differentiating muscle cells

During synchronous differentiation of embryonic chick muscle cells in culture, the Na‐dependent uptake of an amino acid analog, α‐amino isobutyric acid (AIB) undergoes an abrupt, transient increase. The increase in AIB uptake is concomitant with the rapid fusion of mononucleated myoblasts, and precedes the accumulation of muscle‐specific proteins. Subsequently, Nadependent AIB transport diminishes markedly during postfusional differentiation of myotubes. The rate of AIB uptake is increased by insulin both before and after myoblast fusion. This stimulation by insulin is restricted to the Nadependent component of total AIB uptake but is apparently not the result of insulin‐mediated increase in the trans‐membrane Na gradient.