A series of experiments on Nd~3 + influx mediated by the Na~+ /Ca~2 + exchange in human lymphocytes were processed by fura-2 method. The results show that when the cellular Na~+ gradient is reversed, Nd~3 can enter the lymphocytes and voltage dependent calcium channels are not responsible for Nd ~+ influx. It suggests that the Na~+/ Ca ~+ exchange provides a major route for Nd ~+ entry in human lymphocytes. Intracellular free Nd concentrations ([Nd~3]i) are directly proportional to extracellular free Nd~3+ concentrations ([Nd~3+ ]-0) and the maximum [Nd~3+ ]j is (3.67 ±0.32) x 10" mol*L~-1 . [Nd ~+ ]-i decreases with decreasing extracellular pH but increases with decreasing intracellular [Ca~2+ ];. The Ca~+ influx and Nd~3+ influx mediated by the Na~+/Ca~2+ exchange might be mutually competitive. Furthermore, the results also suggest that cytosolic Nd ~+ is transported by the ATP-dependent Ca pump and intracellular Nd ~+ appears to be taken up by endoplasmic reticulum and not be significantly accumulated by mitochondria.

Key words: RARE EARTH, SODIUM ION, CALCIUM ION, NEODYMIUM ION, CELL MEMBRANE, FLUORESCENCE INDICATORS