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 kidney tubular cells. The activity of the exchanger, as well as the membrane vesicle permeability to protons, were monitored by using the pH sensitive dye acridine orange. The membrane vesicle permeability to sodium ions was tested either by using the potential sensitive dye DiS–C2(5) or by using 22Na coupled with the rapid filtration technique. Results indicate that both cadmium and zinc inhibited, in a dose-dependent manner, the activity of the exchanger. However, at the higher tested concentration (0.1 mM) the inhibitory effect exerted by Zinc (90% of inhibition with respect to the control value obtained in the absence of zinc) was significantly (P<0.01) higher than that obtained in the presence of cadmium (42% of inhibition with respect to the control value obtained in the absence of cadmium). Since the inhibitory effect is observed when the zinc and cadmium ions were added in the extravesicular media and since the brush border membrane vesicles are right-side-out oriented, we suggest that both cadmium and zinc act from the external side of the membrane vesicles. In addition results shown in the present paper suggest that zinc inhibited the antiporter activity by interacting with the transporter protein, without any effect on the membrane vesicles permeability both to proton and sodium ions, while the inhibitory effect exerted by cadmium seems to ensue (at least partially) from a change in the membrane vesicles permeability to protons.
Effect of cadmium and zinc on the Na+/H+ exchanger present on the brush border membrane vesicles isolated from eel kidney tubular cells.
VILELLA, Sebastiano;LIONETTO, Maria Giulia;SCHETTINO, Trifone;
2000-01-01
Abstract
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 kidney tubular cells. The activity of the exchanger, as well as the membrane vesicle permeability to protons, were monitored by using the pH sensitive dye acridine orange. The membrane vesicle permeability to sodium ions was tested either by using the potential sensitive dye DiS–C2(5) or by using 22Na coupled with the rapid filtration technique. Results indicate that both cadmium and zinc inhibited, in a dose-dependent manner, the activity of the exchanger. However, at the higher tested concentration (0.1 mM) the inhibitory effect exerted by Zinc (90% of inhibition with respect to the control value obtained in the absence of zinc) was significantly (P<0.01) higher than that obtained in the presence of cadmium (42% of inhibition with respect to the control value obtained in the absence of cadmium). Since the inhibitory effect is observed when the zinc and cadmium ions were added in the extravesicular media and since the brush border membrane vesicles are right-side-out oriented, we suggest that both cadmium and zinc act from the external side of the membrane vesicles. In addition results shown in the present paper suggest that zinc inhibited the antiporter activity by interacting with the transporter protein, without any effect on the membrane vesicles permeability both to proton and sodium ions, while the inhibitory effect exerted by cadmium seems to ensue (at least partially) from a change in the membrane vesicles permeability to protons.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
