Electrophysiological measurements of volume changes in leech neuropile glial cells.
Double-barrelled microelectrodes, sensitive to quaternary ammonium ions, were used for simultaneous measurements of the intracellular free concentrations of choline ([Ch]i) or tetramethylammonium ([TMA]i) as well as membrane potential (Em) in neuropile glial cells of the leech, Hirudo medicinalis. Bath application of Ch or TMA (5 mM, 1 min) resulted in a transient membrane depolarization accompanied by a long-lasting (0.5-1 h) intracellular accumulation of these compounds to levels of between 5 and 15 mM. Changes in [Ch]i or [TMA]i were used for the calculation of changes in relative cell volume. Elevation of the extracellular K+ concentration [( K+]e) from 4 to 9, 15, 21, 27.5, or 40 mM elicited a membrane depolarization and a reversible cell swelling by about 7.5, 14, 18.5, 27 and 50%, whereas reduction of [K+]e to 1.5 mM as well as bath application of serotonin (5-HT) produced a membrane hyperpolarization and a concomitant shrinkage by about 6 and 14.3%, respectively. The measured alterations in cell volume were compared with calculated data based on the assumption of an osmotic equilibrium disturbed by potential-dependent changes of the intracellular Cl- concentration. The results indicate, that K(+)- and serotonin-induced changes in the cell volume of the neuropile glial cells are due to passive KCl and water fluxes.
Ballanyi
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K
Institut für Zoologie I/Neurobiologie, Universität Düsseldorf, Federal Republic of Germany.
Grafe
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Serve
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Schlue
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WR
D000818:Animals; D002794:Choline / Q000493:pharmacokinetics* / Q000494:pharmacology; D004594:Electrophysiology / Q000379:methods*; D007865:Leeches / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D009457:Neuroglia / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000493:pharmacokinetics / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000493:pharmacokinetics* / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D014882:Water-Electrolyte Balance
D000644:Quaternary Ammonium Compounds; D012701:Serotonin; C027917:tetramethylammonium; D002794:Choline; D011188:Potassium