Regulation of CatK expression in cultured rat neonatal atrial myocytes. A, Quantitative real‐time PCR assays showing the expression of CatK mRNA levels in cultured cells treated with and without olmesartan (Olm, 1 μmol/L) in the presence of Ang II (1 μmol/L) or H2O2 (100 μmol/L) for 24 hours. B, Immunofluorescence shows the collagenolytic activity induced by Ang II in cells left untreated or treated with CatK‐II (10 μmol/L) and E64 (10 μmol/L). C, Representative Western blots showing the levels of CatK, gp91phox, p‐p38, and t‐p38 induced by Ang II in cultured neonatal atrial myocytes untreated or treated with Olm (p‐p38MAPK and t‐p38MAPK levels for 30 minutes; CatK and gp91phox levels for 24 hours). D, Quantitative PCR shows Ang II–mediated CatK mRNA expression in cells left untreated or treated with Olm (1 μmol/L), apocynin (Apo, 100 μmol/L), SB202190 (SB, 10 μmol/L), or Apo+SB for 24 hours. Analyzed numbers indicated on related bars. Scale bars indicate 50 μm. Values are expressed as mean±SEM. *P<0.05 vs control; †P<0.01, ‡P<0.001 vs corresponding control. Ang indicates angiotensin II; CatK, cathepsin K; GAPDH, glyceraldehyde‐3‐phosphate dehydrogenase; rMMP1, recombinant matrix metalloproteinase 1.