Studies on human porin XXI: Gadolinium opens up cell membrane standing porin channels making way for the osmolytes chloride or taurine - A putative approach to activate the alternate chloride channel in cystic fibrosis

We recently proposed that cell-membrane-integrated vertebrate porin/voltage -dependent anion-selective channel (VDAC) forms part of the outwardly recti fying chloride channel (ORCC) complex that may be involved in volume regula tion. The results we present here support this thesis, According to light s cattering measurements micromolar concentrations of Gd3+ induce cell swelli ng of human healthy and cystic fibrosis (CF) B-lymphocyte cell lines in iso tonic Ringer solution, In high-potassium Ringer solution additional swellin g is observed, Gd3+ induces excessive cell swelling of cell lines in hypoto nic Ringer solutions, containing 70 mM NaCl or 135 mM taurine, respectively , The gadolinium effect is lost when NaCl is replaced by Na-gluconate, Usin g video camera monitoring we show that HeLa cells also swell in micromolar concentrations of Gd3+ in isotonic taurine Ringer solution. The dose-depend ent effect of the agonist was always blocked by extracellular application o f anti-human type-1 porin antibodies, Together with data on a decreasing ef fect of micromolar amounts of gadolinium on the voltage dependence of recon stituted human porin the results prove the involvement of porin channels in the swelling behavior in different cell lines, As a mechanism we propose t hat ionic gadolinium opens up plasmalemma-integrated porin channels, chlori de or taurine then following their concentration gradients into the cells, Furthermore, our data argue for a single pathway for inorganic and organic osmolytes during regulatory volume decrease after cell swelling. There is i ndirect evidence that porin forms part of the cystic fibrosis relevant ORCC channel, Gadolinium thus may work to open the alternate chloride channel i n CF. (C) 2000 Academic Press.