Polycystic human and rat cholangiocytes show increased metalloprotease activity in culture, associated with alterations in the expression levels of matrix metalloproteases (MMPs) and tissue inhibitor of metalloproteases (TIMPs). (A) Microfluorometric assays for the analysis of MMP activity revealed that polycystic human cholangiocytes possess increased activity compared with normal human cholangiocytes in culture. GM6001 (MMP inhibitor) and recombinant MMP-10 were employed as controls in the assay. (B, C) In addition, changes in mRNA expression levels of different MMPs and TIMPs were found in polycystic human cholangiocytes compared with normal cholangiocyte cultures. Metalloproteases were grouped according to their substrate specificity into collagenases, gelatinases, stromelysins, matrilysins, membrane associated metalloproteases and others, showing global increased expression values in most MMP clusters. n, number of wells analysed in each group.