Effect of ET-1 on procollagen type I and TIMP-1 transcript levels of 1st and 4th passage HSC. Cells were incubated without or with 10-8 M or 10-6 M ET-1 for 48 hours. Total RNA from HSC was reverse transcribed and transcript levels of procollagen α1(I) and TIMP-1 were determined by real time quantitative PCR based on the Taqman technology. Data were normalized to GAPDH mRNA levels. Results are given as mean ± SD (n = 4). **: p < 0.01 vs controls.