Effect of Gd3+ on bradykinin-induced catecholamine secretion from bovine adrenal chromaffin cells.
1. The effects of Gd3+ on bradykinin- (BK-) induced catecholamine secretion, 45Ca2+ efflux and cytosolic [Ca2+] were studied using bovine adrenal chromaffin cells. 2. BK increased secretion in a Ca2+-dependent manner. From 1 - 100 microM, Gd3+ progressively inhibited secretion induced by 30 nM BK to near-basal levels, however from 0.3 - 3 mM Gd3+ dramatically enhanced BK-induced secretion to above control levels. Gd3+ also increased basal catecholamine secretion by 2 - 3 fold at 1 mM. These effects were mimicked by Eu3+ and La3+. 3. Gd3+ enhanced secretion induced by other agonists that mobilize intracellular Ca2+ stores, but simply blocked the response to K+. 4. Gd3+ still enhanced basal and BK-induced secretion in Ca2+-free solution or in the presence of 30 microM SKF96365, however both effects of Gd3+ were abolished after depleting intracellular Ca2+ stores. 5. Gd3+ (1 mM) reduced the rate of basal 45Ca2+ efflux by 57%. In Ca2+-free buffer, BK transiently increased cytosolic [Ca2+] measured with Fura-2. The [Ca2+] response to BK was substantially prolonged in the presence of Gd3+ (1 mM). 6. The results suggest that Gd3+ greatly enhances the efficacy of Ca2+ released from intracellular stores in evoking catecholamine secretion, by inhibiting Ca2+ extrusion from the cytosol. This suggests that intracellular Ca2+ stores are fully competent to support secretion in chromaffin cells to levels comparable to those evoked by extracellular Ca2+ entry. Drugs that modify Ca2+ extrusion from the cell, such as lanthanide ions, will be useful in investigating the mechanisms by which intracellular Ca2+-store mobilization couples to Ca2+-dependent exocytosis.
Bales
P J
PJ
Department of Pharmacology, University of Melbourne, Parkville, Victoria 3052, Australia. p.bales@pharmacology.unimelb.edu.au
Zerbes
M
M
Powis
D A
DA
Marley
P D
PD
D000818:Animals; D001920:Bradykinin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002132:Calcium Radioisotopes; D002413:Cations, Divalent; D002417:Cattle; D019439:Chromaffin Cells / Q000187:drug effects* / Q000378:metabolism*; D004837:Epinephrine / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism / Q000502:physiology; D005456:Fluorescent Dyes; D016257:Fura-2; D005682:Gadolinium / Q000494:pharmacology*; D007424:Intracellular Fluid / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism*; D012636:Secretory Rate / Q000187:drug effects
D002121:Calcium Channel Blockers; D002132:Calcium Radioisotopes; D002413:Cations, Divalent; D005456:Fluorescent Dyes; D005682:Gadolinium; D001920:Bradykinin; D002118:Calcium; D016257:Fura-2; D009638:Norepinephrine; D004837:Epinephrine