Biophys J, July 1998, p. 226-235, Vol. 75, No. 1

Anion Competition for a Volume-Regulated Current

Department of Physiology, Allegheny University of Health Sciences, Philadelphia, Pennsylvania 19129 USA

We have examined whether the anionic amino acids, glutamate and aspartate, permeate through the same volume-regulated conductance permeant to Cl ions. Cell swelling was initiated in response to establishing a whole-cell configuration in the presence of a hyposmotic gradient. Volume-regulated anion currents carried by Cl, glutamate, or aspartate developed with similar time courses and showed similar voltage-dependent inactivation. Permeability ratios (P_aa/P_Cl) calculated from measured reversal potentials were dependent on the mole fraction ratio (MFR) of the permeant anions ([aa]/([aa] + [Cl])). MFR was varied from 0.00 to 0.97. As the fraction of amino acid increased, P_aa/P_Cl decreased. Current amplitude was similarly dependent on MFR. These results show that the permeation of anionic amino acids and that of Cl ions are not independent of each other, indicating that the ion channel underlying the volume-regulated conductance can be occupied by more than one ion at a time. Application of Eyring rate theory indicated that the major barrier to Cl ion permeation is at the intracellular side of the membrane, and that the major barrier to amino acid permeation is at the extracellular side of the membrane. The interactions between these permeant ions may have a physiological modulatory role in volume regulation through a volume-regulated anion conductance.

Biophys J, July 1998, p. 226-235, Vol. 75, No. 1
© 1998 by the Biophysical Society   0006-3495/98/07/226/10  $2.00

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