In our previous observations, adenosine triphosphate (ATP) was found to evoke immediate elevations in intracellular free calcium concentration ([Ca2+]i) in HT4 neuroblastoma cells of mice. We tried to see if a brief pretreatment of glucocorticoids could inhibit the Ca2+ response and reveal the underlying signaling mechanism.
Measurement of [Ca2+]i was carried out using the dual-wavelength fluorescence method with Fura-2 as the indicator.
Preincubation of HT4 cells for 5 min with corticosterone (B) or bovine serum albumin conjugated corticosterone (B-BSA) inhibited the peak [Ca2+]i increments in a concentration-dependent manner. Cortisol and dexamethasone had a similar action, while deoxycorticosterone and cholesterol were ineffective. Both extracellular Ca2+ influx and internal Ca2+ release contributed to ATP-induced [Ca2+]i elevation. The brief treatment with only B attenuated Ca2+ influx. Furthermore, the [Ca2+]i elevation induced by the P2X receptor agonist adenosine 5′-(β,γ-methylene) triphosphate (β,γ-meATP) was also suppressed. The rapid inhibitory effect of B can be reproduced by forskolin 1 mmol/L and blocked by H89 20 mmol/L. Neither nuclear glucocorticoid receptor antagonist mifepristone nor protein kinase C inhibitors influenced the rapid action of B.
Our results suggest that glucocorticoids modulate P2X receptor-medicated Ca2+ influx through a membrane-initiated, non-genomic and PKA-dependent pathway in HT4 cells.
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Project supported by the National Basic Research Program of China (No G1999054003) and the National Natural Science Foundation of China (No 39330100 and 39840019).
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Han, J., Lin, W. & Chen, Y. Inhibition of ATP-induced calcium influx in HT4 cells by glucocorticoids: involvement of protein kinase A. Acta Pharmacol Sin 26, 199–204 (2005). https://doi.org/10.1111/j.1745-7254.2005.00539.x
- adenosine triphosphate
- protein kinase C
- protein kinase A
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