ARC 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 μm ARC 118925XX (ARC; selective P2Y₂ antagonist) strongly suppressed ATP-triggered Ca²⁺ release, suggesting the response was mediated via P2Y₂ 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.