Sodium-channel turnover in rabbit cultured Schwann cells

Radiolabelled saxitoxin has been used as a chemical marker for the voltage-dependent sodium channels expressed in the plasmalemma of rabbit Schwann cells in culture. Proteolytic enzymes destroy this saxitoxin-binding capacity, which gradually reappears with an exponential time constant of about 3.1 days. Exposure of cultured Schwann cells to tunicamycin, an inhibitor of glycosylation, leads to a progressive exponential fall in saxitoxin-binding capacity, again with a time constant of about 3.1 days. The assumption that the steady-state density of Schwann cell sodium channels is maintained by a constant synthesis of channels in the face of a rate of loss from the membrane proportional to the amount of channel already present, leads to the conclusion that these channels have an average lifetime of about 3.1 days. The metabolic consequences of this rapid turnover of Schwann cell sodium channels is discussed.