Probenecid free signal window

Novel fluorophore is more resistant to organic anion exchange proteins found in some cell lines. No signal seen when using FLIPR Calcium 5 Assay Kit without probenecid (Ca5 Kit no PBX). With FLIPR Calcium 6 Assay Kit (Ca6), the signal is smaller without probenecid, however EC50s are conserved and Z' still greater than 0.5.