Effect of cadmium and zinc on the Na+/H+ exchanger present on the brush border membrane vesicles isolated from eel kidney tubular cells

The present paper reports evidence on the effect of cadmium and zinc on the Na+/H+ exchanger activity located on the apical membranes of the eel kidne y tubular cells. The activity of the exchanger. as well as the membrane ves icle permeability to protons, were monitored by using the pH sensitive dye: acridine orange. The membrane vesicle permeability to sodium ions was teste d either by using the potential sensitive dye DiS-C-2(S) or by using Na-22 coupled with the rapid filtration technique. Results indicate that both cad mium and zinc inhibited, in a dose-dependent manner, the activity of the ex changer. However, at the higher tested concentration (0.1 mM) the inhibitor y effect exerted by Zinc (90% of inhibition with respect to the control val ue obtained: in the absence of zinc) was significantly (P < 0.01) higher th an that obtained in the presence of cadmium (42% of inhibition with respect to the control value obtained in the absence of cadmium). Since the inhibi tory effect is observed when the zinc and cadmium ions were added in the ex travesicular media and since the brush border:membrane vesicles are right-s ide-out oriented, we suggest that both cadmium and zinc act from the extern al side of the membrane vesicles. In addition results shown in the present paper suggest that zinc inhibited the antiporter activity by interacting wi th the transporter protein, without any effect on the membrane vesicles per meability both to proton and sodium ions: while the inhibitory effect exert ed by cadmium seems to ensue (at least partially) from a change in the memb rane vesicles permeability to protons. (C) 2000 Elsevier Science B.V. All r ights reserved.