AR-C 118925XX stimulates cation influx in bEND.3 endothelial cells.

In a previous publication when we studied the purinergic receptor with which ATP interacted in mouse brain bEND.3 endothelial cells, we observed addition of 3 mu m ARC 118925XX (ARC; selective P2Y(2) antagonist) strongly suppressed ATP-triggered Ca2+ release, suggesting the response was mediated via P2Y(2) receptors. We here report ARC unexpectedly promoted substantial Ca2+ influx even when ATP-triggered Ca2+ release was largely inhibited. Since this large Ca2+ influx may have important pharmacological significance, we proceeded to investigate its mechanism. ARC did not trigger intracellular Ca2+ release thus suggesting Ca2+ influx triggered by ARC was not store-operated. ARC-triggered Ca2+ influx could be blocked by 1 mm Ni2+, a general Ca2+ channel blocker, but not by SK&F 96365, a nonselective TRP channel blocker. Unexpectedly, ARC promoted influx of Na+ and La3+, but not Mn2+. This is a surprising finding, since Mn2+ is conventionally used as a Ca2+ surrogate ion (as it permeates Ca2+ channel), and La3+ is classically used as a potent Ca2+ channel antagonist. Electrophysiological examination showed ARC did not stimulate any cation currents. Therefore, ARC opened, rather than a cation channel pore, an unidentified Ca2+ influx pathway which was Na+- and La3+-permeable but Mn2+-impermeable.