Abstract
Li+ influx by bovine chromaffin cells, obtained from bovine adrenal medulla, was studied in intact cell suspensions using 7Li NMR spectroscopy with the shift reagent [Tm(HDOTP)]4-. The influx rate constants, ki, were determined in the absence and in the presence of two Na+ membrane transport inhibitors. The values obtained indicate that both voltage sensitive Na+ channels and (Na+/K+)-ATPase play an important role in Li+ uptake by these cells. 7Li NMR T1 and T2 relaxation times for intracellular Li+ in bovine chromaffin cells provided a T1/T2 ratio of 305, showing that Li+ is highly, immobilized due to strong binding to intracellular structures. Using fluorescence spectroscopy and the Mg2+ fluorescent probe, furaptra, the free intracellular Mg2+ concentration in the bovine chromaffin cells incubated with 15 mM LiCl was found to increase by about mM after the intracellular Li+ concentration reached a steady state. Therefore, once inside the cell, Li+ is able to displace Mg2+ from its binding sites.
Highlights
The molecular and cellular mechanisms underlying the clinical use of lithium salts in the treatment of manic-depression as well as other psychiatric and non-psychiatric conditions are still poorly understood [1,2,3]
Even though the experimental conditions were different in our study as compared to the other two [13,33], it is apparent that human erythrocytes accumulate the least amount of Li+; human neuroblastoma cells and bovine chromaffin cells are more similar in the amount of Li+ accumulated
The present study investigates Li+ influx pathways in bovine chromaffin cell suspensions by 7Li NMR
Summary
The molecular and cellular mechanisms underlying the clinical use of lithium salts in the treatment of manic-depression ( called bipolar disease) as well as other psychiatric and non-psychiatric conditions are still poorly understood [1,2,3]. In an attempt to contribute towards a better understanding of this problem, at the cellular and molecular levels, recent studies using fluorescence spectroscopy with the Mg2+ indicator furaptra 10] as well as Li and 31 P NMR spectroscopy [11 have been undertaken. These techniques proved to be useful to investigate Li+ transport [12], Li+ binding [13] and Li+/Mg2+ competition [11,14]. Li+/Mg2+ competition was demonstrated for the phosphate groups of small phosphorylated molecules involved in second messenger systems, such as ATP/ADP, GTP/GDP and IP3 [11,15, 16]; for the phosphate groups of erythrocyte membrane phospholipids [17]; in Li+-loaded human erythrocytes [10,18] and in human SH-SY5Y neuroblastoma cells 14]
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