AJP - Cell Physiology, Vol 257, Issue 1 C141-C146, Copyright © 1989 by American Physiological Society
Cytosolic free magnesium concentration in cultured chick heart cells
S. Rotevatn, E. Murphy, L. A. Levy, B. Raju, M. Lieberman and R. E. London
Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710.
Cytosolic free magnesium (Mgi) was measured in embryonic chick heart cells
loaded with one of two newly developed 19F nuclear magnetic reasonance
(NMR)-sensitive magnesium chelators,
4-methyl,5-fluoro-2-aminophenol-N,N,O-triacetate (MF-APTRA) and
5-fluoro-2-aminophenol-N,N,O-triacetate (5F-APTRA). The cells, embedded in
strands of collagen, were superfused at a rate that allowed for solution
changes in 2 min. In this preparation 19F- and 31P-NMR spectra were stable
for at least 3.5 h. Because Na-coupled Mg countertransport may be a
possible mechanism of Mg transport, in some experiments extracellular Na
was reduced to 1 mM (choline substituted). This manipulation caused a
2.5-fold increase in Mgi from the basal level of 0.56 mM. A significant
proportion of this increase in Mgi could be secondary to an increase in Cai
that occurs with low extracellular Na (Nao) perfusion (Nai-Cao exchange).
Perfusing cells with nominally Ca-free, 1 mM Na salt solution substantially
attenuated the increase in Mgi that occurred with Ca present (1.25 mM) in
the low Na (1 mM) solution. Furthermore, perfusion with 1 mM Na, Mg-free
salt solution caused a 1.5-fold increase in Mgi, which cannot be
attributable to Nai-Mgo exchange. Therefore attempts to describe the
regulation of Mgi in heart cells must differentiate between the effects of
Nai-Mgo exchange and competition for binding sites that are secondary to
stimulation of ion gradient-coupled mechanisms.
