The actions of ouabain and lithium chloride on cytosolic Ca2+ in single chromaffin cells.
The effects of ouabain, Li+ and veratridine on the concentration of cytosolic free Ca2+ ([Ca2+]i) were studied in single fura-2-loaded bovine adrenal chromaffin cells. Superfusion of cells with ouabain (10 microM for 60 min) caused only a delayed mild increase of the Ca2+]i, from around 0.1 microM to 0.2-0.3 microM; this increase was Nao(+)-dependent. Replacement of all NaCl of the Krebs-Hepes solution by LiCl (144 mM) produced a gradual increase of [Ca2+]i, which remained elevated at a stable plateau of 0.4-0.5 microM for 40-50 min. When ouabain (in the presence of normal Nao+) or Li+ (in the absence of Nao+) was given in Krebs-Hepes solution containing no Ca2+, the reintroduction of 2.5 mM Ca2+ produced a fast elevation of the [Ca2+]i. In the case of ouabain-treated cells, the [Ca2+]i curve exhibited an initial phasic component which inactivated to a tonic component. omega-Conotoxin MVIIC (3 microM) and R56865 (10 microM) inhibited the phasic but not the tonic component. Veratridine (30 microM) induced large [Ca2+]i oscillations. Both ouabain or Li+ abolished such oscillations. These results are compatible with ouabain causing elevation of [Ca2+]i in bovine chromaffin cells through a dual mechanism, i.e. cell depolarisation and slowing down of the Na(+)-Ca2+ exchanger of their plasmalemma. Through its binding to the Na+ site on the Na(+)-Ca2+ exchanger, Li+ ions generate powerful Cai2+ signals that might be relevant to its known effects on neurosecretory mechanisms.
De la Fuente
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Departamento de Farmacología, Facultad de Medicina, Universidad Autónoma de Madrid, Spain.
Maroto
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Esquerro
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Sánchez-García
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García
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AG
D000311:Adrenal Glands; D000818:Animals; D018692:Antimanic Agents / Q000494:pharmacology*; D052160:Benzothiazoles; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D002417:Cattle; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D002838:Chromaffin System / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018021:Lithium Chloride / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology*; D010455:Peptides / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D014701:Veratridine / Q000494:pharmacology*; D020960:omega-Conotoxins
D018692:Antimanic Agents; D052160:Benzothiazoles; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D010455:Peptides; D010880:Piperidines; D013844:Thiazoles; D020960:omega-Conotoxins; C075851:omega-conotoxin-MVIIC; D010042:Ouabain; D014701:Veratridine; C054551:R 56865; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D018021:Lithium Chloride; D002118:Calcium