CADMIUM ENHANCES POTASSIUM CONDUCTANCE IN CULTURED RENAL EPITHELOID (MDCK) CELLS

The kidney is a main target organ for cadmium toxicity. The present study has been performed to test for effects of cadmium on electrical properties of cultured subconfluent kidney (MDCK) cells. Cadmium leads to a rapid, sustained and reversible hyperpolarization of the cell membrane, paralleled by an increase of the potassium selectivity and a decrease of the resistance. Thus, cadmium increases the potassium conductance of the cell membrane. The half maximal effect is elicited ≃ 0.2 μM, a concentration encountered during chronic cadmium intoxication. At extracellular calcium concentration reduced to less than 0.1 μM, 5 μM cadmium leads to a transient hyperpolarization, which can be elicited only once. High concentrations (50 μM) of cadmium lead to a sustained hyperpolarization even at extracellular calcium concentrations of less than 0.1 μM. According to fluorescence measurements cadmium leads to an increase of intracellular calcium activity, which is sustained at 1 mM and transient at less than 1 μM extracellular calcium activity. In conclusion, cadmium at low concentrations enhances the potassium conductance in a calcium dependent way. The observations suggest that cadmium enhances intracellular calcium both by recruitment from intracellular stores and by modification of calcium transport across the cell membrane. At high concentrations cadmium enhances the potassium conductance independently from enhanced intracellular calcium activity.