MO082THE EFFECTS OF DIFFERENT MICROMOLAR CONCENTRATIONS OF CADMIUM IONS ON THE PERITUBULAR MEMBRANE POTENTIAL OF PROXIMAL TUBULAR CELLS IN PERFUSED FROG KIDNEYS

Abstract

Abstract Background and Aims Cadmium (Cd2+) is toxic metal and environmental pollutant. Accumulation of cadmium in the kidney results initially in proximal tubule dysfunction. Although Cd2+ toxicity is well documented, all mechanisms that are involved in the early stages of nephrotoxicity, especially considering low micromolar concentrations of Cd2+ ions are still unknown. The Aim of this study was to investigate the effects acute exposure to different peritubular micromolar concentrations of cadmium (0.25, 0.50, 1.0, 2.0, 3.0, 5.0 μmol/L) on the peritubular cell membrane potential in proximal tubular cells of frog kidney. Method The experiments were performed on isolated, doubly perfused kidneys of Rana esculenta of both sexes. Aortic and portal vein were cannulated in order to perfusate luminal and peritubular cell membraine. In controled conditions, Ringer solution was simultaneously used to perfusate both cell membraines. Cadmium chloride (different concentrations: 0.25, 0.50, 1.0, 2.0, 3.0, 5.0 μmol/L) were added to the peritubular perfusate separately, by switching the peritubular perfusate from the control Ringer solution to Ringer solution with addition of cadmium ions. Peritubular cell membrane potentials (PD) were measured with conventional 3 mol/L KCl microelectrodes. Results The peritubular application of different micromolar Cd2+ concentrations led to a rapid, sustained, reversible hyperpolarization of the peritubular cell membrane: 0.25 µmol/L, by −3.3±0.4 mV (n=8, p<0.001); 0.50 µmol/L, by −3.0±0.5 mV (n=11, p<0.001); 1.0 µmol/L, by −2.9±0.6 mV (n=8, p<0.01); 2.0 µmol/L, by −4.2±0.4 mV (n=13, p<0.01); 3.0 µmol/L, by −3.4±0.3 mV (n=14, p<0.001); 5.0 µmol/L, by −3.0±0.4 mV (n=10, p<0.001). After switching the perfusion from Ringer solution with addition of cadmium ions to control Ringer, the peritubular membraine potential returned to the average values that were maintained before the peritubular Cd2+ application (p>0.05). Comparing the effect of different Cd2+ concentrations, there was no difference in the hyperpolarization of the peritubular cell membrane (p>0.05).Each cell served as its own control. Conclusion Different low micromolar concentrations of Cd2+ provoked rapid and sustained hyperpolarization of peritubular membrane potential that did not show concentration-dependent response.