Several hormone agonists exert their physiological actions by triggering an inositol phospholipid—Ca2+ signalling cascade and cytosolic alkalinization. Although calcium ionophores have been used extensively to probe the role of Ca2+ in the regulation of steroidogenesis in granulosa cells, the precise relationship between changes in intracellular Ca2+ (Ca2+i) and pH (pHi) is unclear. In the present study we have used a fluorescent pH indicator, 2′7′-bis-(2-carboxyethyl)-5(and-6)-carboxyfluorescein, to examine the influence of two Ca2+ ionophores, ionomycin and 4-Bromo-A23187 (4-Br-A23187), on pHi in chicken granulosa cells. Chicken granulosa cells from the largest preovulatory follicle were incubated with Ca2+ ionophores (0–2 μm) and/or inhibitors of Na+/H+ antiport (amiloride, dimethylamiloride and ethylisopropyl amiloride; 0·5, 5 and 50 μm respectively) in the presence of Na+ (or choline+; 0–144 mm) and/or Ca2+ (0–10 mm). Ionomycin or 4-Br-A23187 elicited a rapid and sustained cytosolic alkalinization. The magnitude of increase in pHi was dependent on the concentration of the Ca2+ ionophore and the presence of extracellular Ca2+ but independent of extracellular Na+. Pretreatment of the cells with amiloride or its analogues failed to affect the increase in pHi induced by the Ca2+ ionophores significantly. These findings demonstrate that, in addition to their widely reported effects on Ca2+i redistribution in granulosa cells, 4-Br-A23187 and ionomycin cause Ca2+-dependent cytosolic alkalinization. This action of the Ca2+ ionophores is independent of the Na+/H+ antiport. Caution must be exercised in using Ca2+ ionophores as probes to define the role of Ca2+ in the regulation of granulosa cell function.
Journal of Molecular Endocrinology is committed to supporting researchers in demonstrating the impact of their articles published in the journal.
The two types of article metrics we measure are (i) more traditional full-text views and pdf downloads, and (ii) Altmetric data, which shows the wider impact of articles in a range of non-traditional sources, such as social media.
More information is on the Reasons to publish page.
|Sept 2018 onwards||Past Year||Past 30 Days|
|Full Text Views||0||0||0|