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Biophys J, March 2001, p. 1298-1310, Vol. 80, No. 3

Apparent Intracellular Mg2+ Buffering in Neurons of the Leech Hirudo medicinalis

D. Günzel, F. Zimmermann, S. Durry, and W.-R. Schlue

Institut für Neurobiologie, Heinrich-Heine-Universität Düsseldorf, D-40225 Düsseldorf, Germany

The apparent intracellular Mg2+ buffering, or muffling (sum of processes that damp changes in the free intracellular Mg2+ concentration, [Mg2+]i, e.g., buffering, extrusion, and sequestration), was investigated in Retzius neurons of the leech Hirudo medicinalis by iontophoretic injection of H+, OH-, or Mg2+. Simultaneously, changes in intracellular pH and the intracellular Mg2+, Na+, or K+ concentration were recorded with triple-barreled ion-selective microelectrodes. Cell volume changes were monitored measuring the tetramethylammonium (TMA) concentration in TMA-loaded neurons. Control measurements were carried out in electrolyte droplets (diameter 100-200 µm) placed on a silver wire under paraffin oil. Droplets with or without ATP, the presumed major intracellular Mg2+ buffer, were used to quantify the pH dependence of Mg2+ buffering and to determine the transport index of Mg2+ during iontophoretic injecton. The observed pH dependence of [Mg2+]i corresponded to what would be expected from Mg2+ buffering through ATP. The quantity of Mg2+ muffling, however, was considerably larger than what would be expected if ATP were the sole Mg2+ buffer. From the decrease in Mg2+ muffling in the nominal absence of extracellular Na+ it was estimated that almost 50% of the ATP-independent muffling is due to the action of Na+/Mg2+ antiport.

Biophys J, March 2001, p. 1298-1310, Vol. 80, No. 3
© 2001 by the Biophysical Society   0006-3495/01/03/1298/13  $2.00


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