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Modulatory effect of extracellular Mg 2+ ions on K + and Ca 2+ currents of capillary endothelial cells from rat brain
Author(s) -
Delpiano Marco A.,
Altura Burton M.
Publication year - 1996
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(96)00980-5
Subject(s) - extracellular , conductance , chemistry , patch clamp , biophysics , membrane potential , calcium , ion , ion transporter , analytical chemistry (journal) , biochemistry , biology , physics , chromatography , receptor , organic chemistry , condensed matter physics
Using whole‐cell patch‐clamp recording, we demonstrate that exposure of single rat brain capillary endothelial cells to different extracellular Mg 2+ concentrations (0.3, 4.8 and 9.6 mM) affects the conductance of K + and Ca 2+ currents elicited under control conditions (1.2 mM). Extracellular Mg 2+ concentrations ([Mg 2+ ] o ) of 4.8 and 9.6 mM reversibly depress outward K + currents by about 30 ± 12% ( n =10) and 3% ± 13%( n = 10), at all activating potentials, respectively. Using identical concentrations reversibly depressed the Ca 2+ current by about 40 ± 16% ( n = 8) and 46 ± 18% ( n = 6), respectively. Using a low Mg 2+ concentration of 0.3 mM, the K + current activation was unexpectedly and mildly increased by about 15 ± 5% ( n = 5), and the inward Ca 2+ current was attenuated. When studying this effect of low [Mg 2+ ] o on ‘pure’ Ca 2+ currents, free of outward currents, we found that this inward current was depressed by about 38 ± 16% ( n = 8), and its threshold for activation, in the current‐voltage relationship, was shifted to more negative potentials. It is concluded that high [Mg 2+ ] o hinders the entry of Ca 2+ through low‐voltage activated Ca 2+ channels and thereby attenuates a Ca 2+ ‐regulated K + conductance. At a low [Mg 2+ ] o (0.3 mM), Mg 2+ shifts the steady‐state inactivation of the voltage‐activated Ca 2+ channel to more negative potentials by about 8 mV ( n = 6), probably due to a negative screening effect, i.e. a reduction of positive charges on the cell membrane. This may contribute to an apparent increase in K + conductance by an, as yet, unknown mechanism.