Potential role of 12 hydroxyeicosatetraenoic acid in angiotensin II-induced calcium signal in rat glomerulosa cells

Recent evidence suggests that 12 hydroxyeicosatetraenoic acid (¹²HETE), a product of the 12 lipoxygenase (LO) pathway of arachidonic acid metabolism, may have a role in mediating angiotensin II (AII)-induced aldosterone secretion. The present study examined the possible role of the 12 LO product 12HETE in AII-induced calcium ([Ca⁺⁺]_i) signals in rat glomerulosa cells. The addition of 12HETE to glomerulosa cells induced a dose-dependent (10^-6-10^-8 M) rise in [Ca⁺⁺]_i levels that was sustained over 15 min. The effects of 12HETE on [Ca⁺⁺]_i were attenuated but not blocked by nifedipine (5·10^-6 M) and were preserved in a calcium-free medium, suggesting mobilization of intracellular calcium stores. Furthermore, the 12HETE-mediated rise in [Ca⁺⁺]_i was almost entirely abolished by dantrolene. In parallel, 12HETE reversed the inhibitory effect of nifedipine on AII-induced aldosterone secretion [AII (10^-9 M) - 36 ± 7, All + nifedipine (5·10^-6 M) - 13 ± 2, AII + nifedipine + 12HETE (5·10^-8 M) - 27 ± 4 ng/10⁶ cells]. Dantrolene also inhibited AII-dependent aldosterone secretion (AII 10^-9 M - 75.8 ± 5.6, AII + dantrolene 10^-6 M 45.5 ± 8.8 ng/10^-6 cells), but this inhibition could not be reversed by 12HETE 10^-8 M (45.4 ± 10.6 ng/10⁶ cells). The LO blockers baicalein and BW755C inhibited the effect of AII on aldosterone production and on [Ca⁺⁺]_i in a parallel fashion. During LO blockade, the addition of 12HETE (10^-7 M) restored the AII-induced rise in [Ca⁺⁺]_i. Collectively, these observations suggest that activation of the LO pathway in the rat adrenal glomerulosa contributes to changes in cytosolic calcium, which may be important for the steroidogenic effect of AII.