What is the purpose of probenecid in calcium flux flow assays?

The main purpose of probenecid in calcium flux flow assays is to enhance the retention of these dyes and achieve optimal signal sensitivity. Probenecid is a compound which inhibits organic anion transporters and prevents the expulsion of fluorescent dyes from the cells. In a standard calcium flux assay for CHO cells using Fluo-3, Fluo-4, or similar commercial kits, a concentration of 2.5 mM probenecid is recommended.