Catecholamine release from bovine chromaffin cells: the role of sodium-calcium exchange in ouabain-evoked release.
Spontaneous catecholamine (CA) release from bovine chromaffin cells maintained in primary tissue culture has been measured after pre-loading the cells with [3H]noradrenaline. Ouabain inhibited 86Rb+ uptake and increased 3H release in a concentration-dependent manner during a 60 min incubation period. Low external Na+ (5 mM: Li+ substitution) also increased 3H release. Whereas the 3H-releasing action of ouabain was maintained, the Li(+)-evoked release decreased with time. The effects of both ouabain and low Na+ solution on 3H release were completely inhibited by removal of Ca2+ from the external medium even though in Ca2(+)-free solution ouabain further inhibited 86Rb+ uptake into the cells. Readmission of Ca2+ to Na(+)-loaded cells (10-4 M-ouabain in Ca2(+)-free-1 mM-EGTA solution for 60 min) markedly increased the release of 3H. In the additional presence of diphenylhydantoin (DPH, 10-4 M) 3H release was significantly less on Ca2+ readmission. The 3H release from Na(+)-loaded cells was proportional to the concentration of Ca2+ readmitted. The 3H release was further increased from Na(+)-loaded cells in response to Ca2+ readmission when [Na+]o was lowered from 149 to 5 mM (Li+, choline+, Tris+ or sucrose substitution) though Li+ was less effective than the other Na+ substitutes. Potassium removal from the external medium significantly inhibited the 3H release evoked by Ca2+ readmission to Na(+)-loaded cells, even when [Ca2+]o was greater than normal (7.5 mM) or if Ca2+ was readmitted in low [Na+]o solution. Rb+, Cs+ or Li+ could substitute for K+ with the order of potency: Rb+ greater than or equal to K+ greater than Cs+ greater than Li+. A slight increase of external K+ (10.8 mM) potentiated the 3H release from Na(+)-loaded cells on Ca2+ readmission, but a higher concentration of K+ (149.4 mM) had the opposite action. The data is consistent with the hypothesis that ouabain-evoked CA release from bovine chromaffin cells is, in part, a consequence of an internal Na(+)-dependent Ca2+ influx. The evidence also suggests that there is Na(+)-Ca2+ competition at the external arm of the exchanger together with a monovalent cation activation site.
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Neuroscience Group, Faculty of Medicine, University of Newcastle, New South Wales, Australia.
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D000311:Adrenal Glands / Q000166:cytology / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D002838:Chromaffin System / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology*; D010672:Phenytoin / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology
D002352:Carrier Proteins; D002395:Catecholamines; D019831:Sodium-Calcium Exchanger; D013779:Tetrodotoxin; D010042:Ouabain; D010672:Phenytoin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium; D009638:Norepinephrine