New findings concerning vertebrate porin.

Eukaryotic porin can be considered to be a good candidate for forming the channel component of the protein complex which, depending on the approach used, may realize its expression either as the outwardly-rectifying depolarization-induced chloride channel or as the volume-sensitive organic osmolyte-anion channel. As a basis for this proposition, we point to a series of correspondences in properties between mammalian porin and the ORDIC channel complex. Specifically, mammalian porin is expressed in the plasmalemma of different cells and chloride channels can be blocked by anti-human porin antibodies in astrocytes and endothelial cells. There is an indication of colocalisation of human porin and the cystic fibrosis (CF) gene product, CFTR, in the apical region of epithelial cells. The primary structure of porin from a CF patient was found to be normal. Cytosol and amniotic fluid fractions influence the channel characteristics of mammalian porin. Channel-active mammalian porin binds ATP and the stilbene disulphonate grouping of the chloride channel inhibitor DIDS. Human porin in black membranes is a pathway for taurine, and biogenic polyamines reduce the voltage dependence of human porin. Assuming the relationship between human porin and the ORDIC channel/VSOAC complex, studies on plasmalemma-integrated human porin have a relevance for CF research. In addition, we refer to a case study on a child with encephalomyopathy in which porin could not be detected using monoclonal anti-human porin antibodies. Our studies were based on purified and sequenced human porin from different cells and from different cell compartments. In addition, we raised antibodies against mature human porin or synthetic parts of the molecule. This provided a firm foundation for our topochemical work with which we were able to establish the multi-topological expression of eukaryotic porin channels. The data are summarized and discussed.