Original Articles

Inhibition of ATP-induced calcium influx in HT4 cells by glucocorticoids: involvement of protein kinase A

Jian-zhong HAN, Wen LIN, Yi-zhang CHEN


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+]iwas carried out using the
dual-wavelength fluorescence method with Fura-2 as the indicator. Results: 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+]ielevation.
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.