The ouabain-induced [Ca2+]i increase in leech Retzius neurones is mediated by voltage-dependent Ca2+ channels.
In leech Retzius neurones the inhibition of the Na+/K+ pump by ouabain causes an increase in the cytosolic free calcium concentration ([Ca2+]i). To elucidate the mechanism of this increase we investigated the changes in [Ca2+]i (measured by Fura-2) and in membrane potential that were induced by inhibiting the Na+/K+ pump in bathing solutions of different ionic composition. The results show that Na+/K+ pump inhibition induced a [Ca2+]i increase only if the cells depolarized sufficiently in the presence of extracellular Ca2+. Specifically, the relationship between [Ca2+]i and the membrane potential upon Na+/K+ pump inhibition closely matched the corresponding relationship upon activation of the voltage-dependent Ca2+ channels by raising the extracellular K+ concentration. It is concluded that the [Ca2+]i increase caused by inhibiting the Na+/K+ pump in leech Retzius neurones is exclusively due to Ca2+ influx through voltage-dependent Ca2+ channels.
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Institut für Neurobiologie, Heinrich-Heine-Universität Düsseldorf, D-40225, Düsseldorf, Germany. hochstra@uni-duesseldorf.de
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D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects*; D002316:Cardiotonic Agents / Q000494:pharmacology*; D005456:Fluorescent Dyes; D016257:Fura-2; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000187:drug effects; D066298:In Vitro Techniques; D007865:Leeches / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000378:metabolism
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002316:Cardiotonic Agents; D005456:Fluorescent Dyes; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D002118:Calcium; D016257:Fura-2