AJP - Cell Physiology, Vol 248, Issue 1 51-C57, Copyright © 1985 by American Physiological Society
Magnesium transport in murine S49 lymphoma cells: pharmacology and divalent cation selectivity
R. D. Grubbs, C. A. Wetherill, K. Kutschke and M. E. Maguire
The murine S49 lymphoma cell transports Mg2+ by a system distinct from
systems responsible for Ca2+ influx (J. Physiol. London 337: 351-371,
1983). We have now determined the ability of various cations, anions, and
drugs to modulate Mg2+ influx. Neither sulfate, nitrate, phosphate, nor
bicarbonate altered Mg2+ influx. Among cations only T1+, Ba2+, Zn2+, Mn2+,
Sc3+, and La3+ potently inhibited Mg2+ influx without causing obvious cell
toxicity. Seventeen other cations were ineffective at maximal nontoxic
concentrations. T1+ inhibition (Ki = 300 micron) is noncompetitive and
apparently derives from its ability to dissipate membrane potential. The
noncompetitive nature of and the rather poor inhibition constants for Ca2+
(Ki approximately equal to 5 mM) and Mn2+ (Ki = 200 micron) indicate that
neither cation is an effective physiological antagonist of Mg2+ influx.
Only Ba2+ exhibited competitive inhibition of Mg2+ influx (Ki = 1 mM).
Cisplatin and Ca2+ channel antagonists also did not inhibit Mg2+ influx.
These data further differentiate Mg2+ transport systems from those for
Ca2+. In addition, the selectivity series for group IIa cation inhibition
of influx (Mg2+ greater than Ba2+ much greater than Ca2+ greater than or
equal to Sr2+) has not been observed previously in biological systems and
is indicative of a very high anionic field strength at the Mg2+ recognition
site.
