Quantitative RT-PCR analysis of MDR1 mRNA. Reactions were performed as described in Materials and Methods. A representative experiment is shown. All reactions contained 100 ng total RNA. Internal standard (upper band) 212 bp, MDR1 mRNA (lower band) 161 bp. SM: Size marker (HaeIII digest ◊X174 DNA); 1: negative control (no RT); 2: 0.05 pg ISC RNA; 3: 0.25 pg ISC RNA; 4: 0.5 pg ISC RNA; 5: 1.0 pg ISC RNA; 6: 2.5 pg ISC RNA.