Inhibition of ATP-induced calcium influx in HT4 cells by glucocorticoids: involvement of protein kinase A.
OBJECTIVE
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'-(beta, gamma-methylene) triphosphate (beta, gamma-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.


CONCLUSIONS
Our results suggest that glucocorticoids modulate P2X receptor-medicated Ca2+ influx through a membrane-initiated, non-genomic and PKA-dependent pathway in HT4 cells.
Han
Jian-Zhong
JZ
Neuroscience Research Institute and Department of Neurobiology, College of Pharmacy, Second Military Medical University, Shanghai 200433, China.
Lin
Wen
W
Chen
Yi-Zhang
YZ
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D045744:Cell Line, Tumor; D003345:Corticosterone / Q000494:pharmacology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006854:Hydrocortisone / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology; D051379:Mice; D009447:Neuroblastoma / Q000473:pathology; D058910:Purinergic P2 Receptor Agonists; D058469:Receptors, Purinergic P2X; D012709:Serum Albumin / Q000494:pharmacology; D015398:Signal Transduction; D013449:Sulfonamides / Q000494:pharmacology
D007546:Isoquinolines; D058910:Purinergic P2 Receptor Agonists; D058469:Receptors, Purinergic P2X; D012709:Serum Albumin; D013449:Sulfonamides; C005147:5'-adenylyl (beta,gamma-methylene)diphosphonate; D003907:Dexamethasone; D000255:Adenosine Triphosphate; D017868:Cyclic AMP-Dependent Protein Kinases; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D002118:Calcium; D003345:Corticosterone; D006854:Hydrocortisone