Mechanism of Cl-sensitivity in internal ion receptors of the leech; an inward current gated off by Cl-in the nephridial nerve cells
✍ Scribed by A. Wenning; R. L. Calabrese
- Publisher
- Springer
- Year
- 1991
- Tongue
- English
- Weight
- 730 KB
- Volume
- 168
- Category
- Article
- ISSN
- 0340-7594
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✦ Synopsis
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.