SINGLE POTASSIUM CHANNELS IN NEUROPIL GLIAL-CELLS OF THE LEECH CENTRAL-NERVOUS-SYSTEM

We performed patch-clamp experiments to identify distinct K+ channels underlying the high K+ conductance and K+ uptake mechanism of the neur opile glial cell membrane on the single-channel level. In the soma mem brane four different types of K+ channels were characterized, which we re found to be distributed in clusters. Since no other types of K+ cha nnels were observed, these appear to be the complete repertoire of Kchannels expressed in the soma region of this cell type. The outward r ectifying 42 pS K+ channel could markedly contribute to the high K+ co nductance and the maintenance of the membrane potential, since it show s the highest open probability of all channels. The channel gating occ urred in bursts and patch excision decreased the open probability. The outward rectifying 74 pS K+ channel was rarely active in the cell-att ached configuration; however, patch excision enhanced its open probabi lity considerably. This type of channel may be involved in neuron-glia l crosstalk, since it is activated by both depolarizations and increas es in the intracellular Ca2+ concentration, which are known to be indu ced by neurotransmitter release following the activation of neurons. T he 40 pS and 83 pS K+ channels showed inward rectifying properties, su ggesting their involvement in the regulation of the extracellular K+ c ontent. The 40 pS K+ channel could only be observed in the inside-out configuration. The 83 pS channel was activated following patch excisio n. At membrane potentials more negative than -60 mV, flickering events indicated voltage-dependent gating. (C) 1997 Elsevier Science B.V.