Cadmium inhibition of l-alanine transport into renal brush border membrane vesicles isolated from the winter flounder ( Pseudopleuronectes americanus)

Using isolated brush border membrane vesicles from the kidney of the winter flounder ( Pseudopleuronectes americanus), we have studied the effect of cadmium on l-alanine transport. Pretreatment of vesicles with 0.1 m m Cd 2+ resulted in inhibition of l-alanine uptake in the presence of a NaCl (but not KCl) gradient. Inhibition was due to a specific interaction with the sodium-alanine cotransport system and not a change in the driving forces for alanine transport, since Cd 2+ did not affect sodium-dependent d-glucose uptake. The effect of Cd 2+ on Na +-alanine cotransport showed mixed-type inhibition which is only partially reversible by EDTA. Cd 2+ uptake itself was shown to be time and temperature dependent, resulting in binding to both sides of the membrane. No direct correlation was possible between inhibition of l-alanine transport and the amount of Cd 2+ taken up by the membranes. Nevertheless, the striking time dependence of the effect of Cd 2+ on sodium-dependent l-alanine uptake and the inability of EDTA to reverse the inhibitory action of Cd 2+ suggest that Cd 2+ inhibits Na +-alanine cotransport at the cytoplasmic side of the membrane.