Chloride conductance and volume-regulatory nonselective cation conductance in human red blood cell ghosts

Abstract.

To identify the ion channels involved in erythrocyte volume regulation, whole-cell currents from human red blood cells (RBCs) were recorded in isotonic, hypotonic and hypertonic media. In isotonic NaCl bath solution, whole-cell currents rectified outwardly with reversal potentials (V _rev) between the equilibrium potential of Cl^– (E _Cl) and that of nonselective cations (NSC), E _NSC. Replacement of bath Cl^– by gluconate decreased outward conductance (G _outward) by 43±6% (n=5) and shifted V _rev with E _Cl indicating a high fractional Cl^– conductance. Hypotonic cell swelling reversibly decreased G _outward by 23±3% (n=8) while hypertonic cell shrinkage reversibly increased G _outward by 27±8% (n=5). These shrinkage-activated and swelling-inactivated current fractions rectified outwardly with V _rev at E _NSC suggesting that both fractions are generated by the same type of NSC channel. The shrinkage-activated ΔG _outward decreased from 4.7±1.2 nS (n=3) to 1.4±0.4 nS (n=5) and 0.5±0.4 nS (n=7) with the increase of pipette [Cl^–] from 7 mM to 39 mM and 139 mM, respectively. Similarly, with this increase of pipette [Cl^–], G _outward under isotonic control conditions decreased from 8.2±1.4 nS (n=5) to 7.4±1.0 nS (n=20) and 4.1±0.7 nS (n=17), due to the differing activity of these NSC channels. In conclusion, human RBCs express, besides a high fractional Cl^– conductance, NSC channels that are regulated by cell volume and the cytosolic [Cl^–].