SINGLE-ION CHANNEL CURRENTS IN NEUROPIL GLIAL-CELLS OF THE LEECH CENTRAL-NERVOUS-SYSTEM

The patch-clamp technique was used to investigate the activity of sing le ion channels in neuropile glial (NG) cells in the central nervous s ystem (CNS) of the medicinal leech, Hirudo medicinalis. We found evide nce for two distinct Cl- channels that could be distinguished by their basic electrical properties and their responses to different inhibito rs on single ion channel currents. In the inside-out configuration in symmetrical Cl- solutions, these channels showed current-voltage relat ionships with slight outward rectification, mean conductances of 70 an d 80 pS, and reversal potentials near 0 mV. Significant permeability t o Na+, K+, or SO42- could not be detected. The open-state probability of the 70 pS Cl- channel increased with membrane depolarization, where as the open-state probability of the 80 pS Cl- channel was voltage-ind ependent. The application of the stilbene derivative DIDS (100 muM) to the cytoplasmic side of the glial cell membrane blocked both Cl- chan nels. The activity of the 70 pS channel was blocked irreversibly by DI DS, whereas the activity of the 80 pS channel reappeared after wash-ou t of DIDS. Both channels were blocked reversibly by 1 mM Zn2+. K+ chan nels could only be observed occasionally in the soma membrane of the N G cells. We have characterized a 60 pS K+ channel with a high selectiv ity for K+ over Na+. The low density of K+ channels in the soma membra ne may indicate a non-uniform distribution of this channel type in NG cells. (C) 1993 Wiley-Liss, Inc.