title: Li influx and binding, and li/mg competition in bovine chromaffin cell suspensions as studied by li NMR and fluorescence spectroscopy.
abstract: Li(+) influx by bovine chromaffin cells, obtained from bovine adrenal medulla, was studied in intact cell suspensions using (7)Li NMR spectroscopy with the shift reagent [Tm(HDOTP)](4-). The influx rate constants, k(i), 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. (7)Li NMR T(1) and T(2) relaxation times for intracellular Li(+) in bovine chromaffin cells provided a T(1)/T(2) ratio of 305, showing that Li(+) is highly, immobilized due to strong binding to intracellular structures. Using fluorescence spectroscopy and the Mg(2+) fluorescent probe, furaptra, the free intracellular Mg(2+) 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 Mg(2+) from its binding sites.
authors.affiliation: Department of Biochemistry University of Coimbra P.O. Box 3126 Coimbra 3000 Portugal.
authors.forename: C P
authors.initials: CP
authors.lastname: Fonseca
authors.forename: L P
authors.initials: LP
authors.lastname: Montezinho
authors.forename: G
authors.initials: G
authors.lastname: Baltazar
authors.forename: B
authors.initials: B
authors.lastname: Layden
authors.forename: D M
authors.initials: DM
authors.lastname: Freitas
authors.forename: C F
authors.initials: CF
authors.lastname: Geraldes
authors.forename: M M
authors.initials: MM
authors.lastname: Castro