Probenecid inhibits SBFI leakage from neonatal rat cardiomyocytes. Adherent cardiomyocytes on a 96-well microplate were loaded with 5 μM SBFI-AM for 90 min at room temperature. Cells were washed twice and incubated in Tyrode solution in the presence or absence of 1 mM probenecid. The fluorescence intensity was measured every 5 min. (A) The time course of the background-subtracted SBFI fluorescence intensity at 340 nm (F340). (B) The time course of the background-subtracted SBFI fluorescence intensity at 380 nm (F380). (C) The relative SBFI fluorescence ratio (F340/F380), with the ratio at 80 min in each group considered to be 100%. Solid lines, without probenecid; dashed lines, with probenecid. *P < 0.05 vs cells treated without probenecid. The data are the means ± SE from four experiments.