Amiloride inhibits hydrogen peroxide-induced Ca2+ responses in human CNS pericytes

The aims of the present study were to investigate the mechanisms of Ca2+ signaling caused by hydrogen peroxide in CNS pericytes. In cultured human brain microvascular pericytes, cytosolic Ca2+ concentration was measured by means of fura-2 fluorescence. Reverse transcription and polymerase chain reaction was performed to examine the expression of mRNA. Knockdown of Na+/H+ exchanger (NHE) was done by transfecting the cells with specific double-strand siRNAs for NHE. Externally applied hydrogen peroxide dose-dependently (100 μM–10 mM) increased cytosolic Ca2+ in human CNS pericytes. Cytosolic Ca2+ remained high after wash-out of hydrogen peroxide. However, the addition of dithiothreitol rapidly reversed cytosolic Ca2+ to the resting level. The hydrogen peroxide-induced Ca2+ increase was not inhibited by nicardipine, Gd3+, La3+, or omission of external Ca2+. Neither thapsigargin nor carbonyl cyanide 4-trifluoromethoxyphenylhydrazone attenuated the hydrogen peroxide-induced Ca2+ rise. Amiloride and its derivatives, benzamil and hexamethylene amiloride reversed the hydrogen peroxide-induced Ca2+ increase. Human CNS pericytes expressed acid sensing ion channel (ASIC) 1a, Na+/Ca2+ exchanger (NCX) 1, Na+/H+ exchanger (NHE) 1, and NHE7. However, the removal of external Na+, treatment with KB-R 7943 and mibefradil, or knockdown of NHE1 and NHE7 did not affect the hydrogen peroxide-induced Ca2+ increase. Hydrogen peroxide releases Ca2+ from intracellular Ca2+ pool via an amiloride-sensitive protein, which is controlled by oxidation of thiol group in human CNS pericytes.