Quantitative analysis of the cytosolic-free-Ca2+-dependency of aldosterone production in bovine adrenal glomerulosa cells. Different requirements for angiotensin II and K+.
Angiotensin II (AII) and K+ raise the cytosolic free Ca2+ concentration [( Ca2+]i) and stimulate aldosterone production in isolated bovine adrenal glomerulosa cells. The mechanisms leading to an elevation of [Ca2+]i were analysed with the fluorescent Ca2+ probe quin 2. (1) Whereas [Ca2+]i rose transiently and returned to basal values within 5 min in response to AII, the effect of K+ was sustained for at least 15 min. (2) AII released Ca2+ from intracellular stores, whereas the [Ca2+]i response to K+ depended solely on extracellular [Ca2+]. (3) When added after K+ stimulation, AII provoked a dramatic decrease in [Ca2+]i to below the resting value. The role of [Ca2+]i in stimulating steroidogenesis was determined by manipulating the concentration of this cation. (4) In a cell superfusion system, the aldosterone response to AII is biphasic. Suppressing the transient [Ca2+]i elevation triggered by AII resulted in the disappearance of the initial secretory peak, but the final production rate was similar to that of control cells. (5) Normal basal [Ca2+]i levels were, however, necessary to maintain continuous AII-induced steroidogenesis. (6) When added after AII, the antagonist analogue [Sar1,Ala8]AII suppressed steroidogenesis without affecting [Ca2+]i levels. (7) In contrast, continuously elevated [Ca2+]i values were required for the initiation and the maintenance of K+-stimulated aldosterone production. These results demonstrate important differences in the mechanisms through which AII and K+ activate the Ca2+ messenger system. Moreover, functional correlations have shown that K+, but not AII, depends solely on a sustained [Ca2+]i response for its steroidogenic effect. However, the AII-induced effect is also a Ca2+-requiring process: the initial [Ca2+]i transient accelerates the onset of steroidogenesis, which is subsequently extremely sensitive to [Ca2+]i decreases below normal basal levels.
Division of Endocrinology, University Hospital, Geneva, Switzerland.
A M
AM
Capponi
P D
PD
Lew
M B
MB
Vallotton
D000302:Adrenal Cortex / Q000187:drug effects / Q000378:metabolism*; D000450:Aldosterone / Q000378:metabolism*; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology*; D011945:Receptors, Angiotensin / Q000378:metabolism; D012504:Saralasin / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D013256:Steroids / Q000096:biosynthesis
D011945:Receptors, Angiotensin; D013256:Steroids; D000804:Angiotensin II; D000450:Aldosterone; D012504:Saralasin; D011188:Potassium; D002118:Calcium