Effects of ouabain on intracellular ion activities of sensory neurons of the leech central nervous system.
1. The intracellular K+, Na+, and Ca2+ of mechanosensory neurons in the central nervous system of the leech Hirudo medicinalis was measured using double-barreled ion-sensitive microelectrodes. 2. After inhibition of the Na(+)-K+ pump with 5 x 10(-4) M ouabain, the intracellular K+ activity (aKi) decreased, while the intracellular Na+ activity (aNai) increased. The input resistance decreased in the presence of ouabain. The intracellular Ca2+ increased more than one order of magnitude after ouabain addition. All changes in intracellular ion activities and membrane resistance were fully reversible. 3. When extracellular Na+ concentration ([Na+]o) was removed [replaced by tris(hydroxymethyl)aminomethane (Tris)], aNai decreased. In the absence of [Na+]o, aKi and aNai remained unchanged after inhibition of the Na(+)-K+ pump by reducing the extracellular K+ concentration ([K+]o) to 0.2 mM. The membrane resistance increased under these conditions. 4. The intracellular Ca2+ decreased or remained constant after removal of [Na+]o. Addition of ouabain in the absence of [Na+]o did not change intracellular Ca2+, which only increased after readdition of [Na+]o. 5. The relative K+ permeability (PK) measured as membrane potential change during a brief increase of the [K+]o from 4 to 10 mM, increased manyfold after addition of ouabain but only little if [Na+]o had been removed before adding ouabain. 6. The results suggest that the intracellular Na+ increase after inhibition of the Na(+)-K+ pump affects the intracellular Ca2+ level by stimulating a Nai(+)-Ca2+ exchange mechanism. The subsequent intracellular Ca2+ activity (aCai) rise may result in an increase of the membrane permeability to K+ ions.
Schlue
W R
WR
Institut für Zoologie/Lehrstuhl für Neurobiologie, Heinrich-Heine-Universität Düsseldorf, Federal Republic of Germany.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002490:Central Nervous System / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D004594:Electrophysiology; D007473:Ion Channels / Q000187:drug effects*; D007865:Leeches / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D008839:Microelectrodes; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
D007473:Ion Channels; D010042:Ouabain; D012964:Sodium; D011188:Potassium; D002118:Calcium