Forms pores that allow passive diffusion of small molecules across the outer membrane. (Microbial infection) Supports colicin E5 entry in the absence of its major receptor OmpF. (Microbial infection) A mixed OmpC-OmpF heterotrimer is the outer membrane receptor for toxin CdiA-EC536; polymorphisms in extracellular loops 4 and 5 of OmpC confer susceptibility to CdiA-EC536-mediated toxicity. Homotrimer (PubMed:2464593, PubMed:16949612). Forms mixed heterotrimers with OmpF and with PhoE; other mixed heterotrimers are also probable (PubMed:2464593). By growth in high osmolarity conditions (high sugar or salt) under control of OmpR (at protein level) (PubMed:3010044, PubMed:2464593). In the presence of 0.2 M NaCl, 2.0 mM sodium cholate (bile salts) decreases expression from the ompC promoter; how this is mediated is unknown (PubMed:28423182). Loop L3 (residues 116-133) extends along the inner side of the beta barrel wall and may constrict the pore mid-length. Deletion of both ompC and ompF confers resistance to colicin E5 and to the toxic activity of CdiA-EC536. Binds 1 Mg(2+) per subunit; could be Ca(2+) in vivo. Belongs to the Gram-negative porin family.