Sodium-sensitive, calcium-independent potassium conductance in the leech giant glial cell.
We have measured membrane current, membrane potential and intracellular Na+ and Ca2+ concentrations, [Na+]i and [Ca2+]i, of the giant glial cell in the nervous system of the leech Hirudo medicinalis using conventional microelectrodes and the fluorescent dyes sodium-binding benzofuran isophthalate (SBFI) and fura-2. When the Na+ was removed from the saline, the membrane conductance increased twofold from 1.29±0.1 µS to 2.57±0.18 µS (mean ± SEM; n=27). The rise in membrane conductance was accompanied by a current, which reversed around –74 mV, and the amplitude of K+-induced depolarizations or currents increased during Na+ removal, suggesting an increase in the K+ conductance of the glial membrane. We also monitored [Ca2+]i when removing external Na+ in the presence and absence of external Ca2+, and during injection of the Ca2+-chelator BAPTA into the cells. Our results indicate that Na+ modulates a K+ conductance of these glial cells, independent of intra- and extracellular Ca2+.
Abteilung für Allgemeine Zoologie, FB Biologie, Universität Kaiserslautern, Postfach 3049, D-67653 Kaiserslautern, Germany.
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Deitmer
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002614:Chelating Agents / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D007865:Leeches / Q000166:cytology* / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D009457:Neuroglia / Q000166:cytology / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
D002614:Chelating Agents; D004533:Egtazic Acid; D012964:Sodium; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D011188:Potassium; D002118:Calcium