On-line identification of P-glycoprotein substrates by monitoring of extracellular acidification and respiration rates in living cells

► Identification of P-gp substrates by a label-free cytosensor assay. ► P-gp substrates induce cellular acidification and respiration. ► Effects were concentration dependent (Michaelis-Menten type kinetics). ► Inhibitors of P-gp demonstrate specificity of the assay. ► P-gp deficient control cells showed no stimulation effects.