Acta Pharmacologica Sinica 2005 February; 26 (2): 199-204; doi: 10.1111/j.1745-7254.2005.00539.x

Aim: 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.

Methods: Measurement of [Ca²⁺]_i was carried out using the dual-wavelength fluorescence method with Fura-2 as the indicator.

Results: Pre-incubation 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.

Conclusion: Our results suggest that glucocorticoids modulate P2X receptor-medicated Ca²⁺ influx through a membrane-initiated, non-genomic and PKA-dependent pathway in HT4 cells.

Keywords: calcium; glucocorticoids; adenosine tri-phosphate; protein kinase C; protein kinase A