Abundance of surrogate peptides for canalicular and sinusoidal transporter proteins was quantified from digested plasma membrane extractions derived from sandwich-cultured upcyte and primary hepatocytes (SCUHH and SCHH), respectively. In cases in which concentrations were found below 1 fmol/µg protein and the corresponding peak area of detected signals of at least two MRM transitions was below 5000 counts, the LOQ was defined as described by Uchida et al. (2011). In brief, the protein level of a signature peptide equivalent to a peak area of 5000 counts was calculated based on the linear regression equations obtained from calibrations curves (determination coefficient r² > 0.99; Supplemental Table 4). If signal peaks were not detectable for two or more MRM transitions of a signature peptide, the corresponding transporter protein was defined as not quantifiable and was considered not to be present in the corresponding UHH culture, applying the quantitative targeted absolute proteomics method described herein. LOQ and ULQ values were as follows: LOQ_MATE1 = 0.334 fmol/µg plasma membrane protein; LOQ_OATP1B1 = 0.338 fmol/µg plasma membrane protein; LOQ_BSEP = 0.467 fmol/µg plasma membrane protein; and ULQ_OCT1 = 100 fmol/µg plasma membrane protein. NQ, not quantifiable; ULQ, upper limit of quantification.