Single potassium channels in neuropile 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 neuropile glial cell membrane on the single-channel level. In the soma membrane four different types of K+ channels were characterized, which were found to be distributed in clusters. Since no other types of K+ channels were observed, these appear to be the complete repertoire of K+ channels expressed in the soma region of this cell type. The outward rectifying 42 pS K+ channel could markedly contribute to the high K+ conductance and the maintenance of the membrane potential, since it shows the highest open probability of all channels. The channel gating occurred in bursts and patch excision decreased the open probability. The outward rectifying 74 pS K+ channel was rarely active in the cell-attached configuration; however, patch excision enhanced its open probability considerably. This type of channel may be involved in neuron-glial crosstalk, since it is activated by both depolarizations and increases in the intracellular Ca2+ concentration, which are known to be induced by neurotransmitter release following the activation of neurons. The 40 pS and 83 pS K+ channels showed inward rectifying properties, suggesting their involvement in the regulation of the extracellular K+ content. The 40 pS K+ channel could only be observed in the inside-out configuration. The 83 pS channel was activated following patch excision. At membrane potentials more negative than -60 mV, flickering events indicated voltage-dependent gating.