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Updated: Aug 14, 2026

Intracellular Recording, Sensory Field Mapping, and Culturing Identified Neurons in the Leech, Hirudo medicinalis
Published on: November 5, 2013
Indirectly gated Cl(-)-dependent Cl(-) channels sense physiological changes of extracellular chloride in the leech
A Wenning1, C F Erxleben, R L Calabrese
1Fakultät für Biologie, Universität Konstanz, D-78457 Konstanz, Germany. awenning@biology.emory.edu
Abstract:
The maintenance of ion homeostasis requires adequate ion sensors. In leeches, 34 nephridial nerve cells (NNCs) monitor the Cl(-) concentration of the blood. After a blood meal, the Cl(-) concentration of leech blood triples and is gradually restored to its normal value within 48 h after feeding. As previously shown in voltage-clamp experiments, the Cl(-) sensitivity of the NNCs relies on a persistent depolarizing Cl(-) current that is turned off by an increase of the extracellular Cl(-) concentration. The activation of this Cl(-)-dependent Cl(-) current is independent of voltage and of extra- and intracellular Ca(2+). The transduction mechanism is now characterized on the single-channel level. The NNC's sensitivity to Cl(-) is mediated by a slowly gating Cl(-)-dependent Cl(-) channel with a mean conductance of 50 pS in the cell-attached configuration. Gating of the Cl(-) channel is independent of voltage, and channel activity is independent of extra- and intracellular Ca(2+). Channel activity and the macroscopic current are reversibly blocked by bumetanide. In outside-out patches, changes of the extracellular Cl(-) concentration do not affect channel activity, indicating that channel gating is not via direct interaction of extracellular Cl(-) with the channel. As shown by recordings in the cell-attached configuration, the activity of the channels under the patch is instead governed by the Cl(-) concentration sensed by the rest of the cell. We postulate a membrane-bound Cl(-)-sensing receptor, which-on the increase of the extracellular Cl(-) concentration-closes the Cl(-) channel via a yet unidentified signaling pathway.
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