For MDCK/hOAT1 cells, the rate was 9.94 ± 0.79 pmol/mg protein/min for treating with [3H]-PAH only, whereas the addition of probenecid dramatically diminished the rate to 0.54 ± 0.01 pmol/mg protein/min. This evidence concerns the gene SLC22A6 and pulmonary arterial hypertension.