Intracellular chloride regulation in amphibian dorsal root ganglion neurones studied with ion‐selective microelectrodes.

Abstract

1. Intracellular Cl‐ activity (aiCl) and membrane potential (Em) were measured in frog dorsal root ganglion neurones (DRG neurones) using double‐barrelled Cl‐ ‐selective microelectrodes. In standard Ringer solution buffered with HEPES (5 mM), equilibrated with air or 100% O2, the resting membrane potential was ‐57.7 +/‐ 1.0 mV and aiCl was 23.6 +/‐ 1.0 mM (n = 53). The value of aiCl was 2.6 times the activity expected for an equilibrium distribution and the difference between Em and ECl was 25 mV. 2. Removal of external Cl‐ led to a reversible fall in aiCl. Initial rates of decay and recovery of aiCl were 4.1 and 3.3 mM min‐1, respectively. During the recovery of aiCl following return to standard Ringer solution, most of the movement of Cl‐ occurred against the driving force for a passive distribution. Changes in aiCl were not associated with changes in Em. Chloride fluxes estimated from initial rates of change in aiCl when external Cl‐ was removed were too high to be accounted for by electrodiffusion. 3. The intracellular accumulation of Cl‐ was dependent on the extracellular Cl‐ activity (aoCl). The relationship between aiCl and aoCl had a sigmoidal shape with a half‐maximal activation of about 50 mM‐external Cl‐. 4. The steady‐state aiCl depended on the simultaneous presence of extracellular Na+ and K+. Similarly, the active reaccumulation of Cl‐ after intracellular Cl‐ depletion was abolished in the absence of either Na+ or K+ in the bathing solution. 5. The reaccumulation of Cl‐ was inhibited by furosemide (0.5‐1 x 10(‐3) M) or bumetanide (10(‐5) M). The decrease in aiCl observed in Cl‐ ‐free solutions was also inhibited by bumetanide. 6. Cell volume changes were calculated from the observed changes in aiCl. Cells were estimated to shrink in Cl‐ ‐free solutions to about 75% their initial volume, at an initial rate of 6% min‐1. 7. The present results provide direct evidence for the active accumulation of Cl‐ in DRG neurones. The mechanism of Cl‐ transport is electrically silent, dependent on the simultaneous presence of external Cl‐, Na+ and K+ and inhibited by loop diuretics. It is suggested that a Na+:K+:Cl‐ co‐transport system mediates the active transport of Cl‐ across the cell membrane of DRG neurones.