INTRACELLULAR CHLORIDE ACTIVITY IN GLIAL-CELLS OF THE LEECH CENTRAL-NERVOUS-SYSTEM

1. Chloride‐sensitive double‐barrelled microelectrodes were used to measure the intracellular Cl‐ activity (aicl) and membrane potential (Em) in neuropile glial cells of the leech, Hirudo medicinalis. 2. A close relation between the equilibrium potential for Cl‐ (ECl = ‐66.1 +/‐ 4.9 mV; mean +/‐ S.D.) and the resting potential (Em = ‐67.8 +/‐ 5.2 mV; n = 19) was observed in nominally CO2‐HCO3(‐)‐free, HEPES‐buffered solutions. A saline buffered with 2% CO2, 11 mM‐HCO3‐ elicited a membrane hyperpolarization and a concomitant decrease of aCl. 3. Changes in ECl followed these of Em with a lag of less than 30 s in response to various extracellular K+ concentrations [( K+]o) or due to bath‐application of carbachol or serotonin. 4. Introduction of a Cl(‐)‐free solution resulted in a transient depolarization indicating a substantial Cl‐ conductance and a rapid decrease of aiCl to an apparent value of 0.5‐0.9 mM. 5. The loop diuretics furosemide (1 mM) and bumetanide (0.2 mM) did not affect the K(+)‐induced changes of aiCl. 6. The results indicate a passive Cl‐ distribution across the membrane of leech neuropile glial cells as a result of a high Cl‐ conductance. © 1990 The Physiological Society