Mechanism of Cl- sensitivity in internal ion receptors of the leech: an inward current gated off by Cl- in the nephridial nerve cells.
The nephridial nerve cells of the leech, Hirudo medicinalis, 34 sensory cells, each associated with one nephridium, are sensitive to changes in extracellular Cl- concentration, an important factor in ion homeostasis. Using single-electrode current- and voltage clamp and ion substitution techniques, the specificity and mechanism of Cl- sensitivity of the nephridial nerve cell was studied in isolated preparations. Increase of the normally low external Cl- concentration leads to immediate and sustained hyperpolarization, decrease of the frequency of bursts and decrease of membrane conductance. The response is halogen specific: Cl- can be replaced by Br-, but not by organic mono- or divalent anions or inorganic divalent anions. At physiological Cl- concentrations (36 mM extracellular Cl-), the nephridial nerve cell has a high resting conductance for Cl- and the membrane potential is governed by Cl-. In high extracellular Cl- concentrations (110-130 mM), membrane conductance is low, most likely due to the gating off of Cl- channels. Under these conditions, membrane potential is dominated by the K+ distribution and the nephridial nerve cell hyperpolarizes towards EK.
Wenning
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Fakultät für Biologie, Universität Konstanz, Federal Republic of Germany.
Calabrese
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RL
D000818:Animals; D002712:Chlorides / Q000378:metabolism / Q000494:pharmacology*; D004558:Electric Stimulation; D004566:Electrodes; D004594:Electrophysiology; D015640:Ion Channel Gating / Q000187:drug effects*; D007865:Leeches / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D009431:Neural Conduction / Q000187:drug effects; D009469:Neuromuscular Junction / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology
D002712:Chlorides; D011188:Potassium