CHARACTERIZATION OF CYTOSOLIC CL- CHANNEL INHIBITORS BY SIZE-EXCLUSION CHROMATOGRAPHY

Cytosol prepared from human placenta inhibits outwardly rectifying Cl- channels excised from HT29 cells. Size exclusion chromatography of cytosol on Superose 12 revealed two inhibitory fractions suggesting Cl- channel inhibitors of different size or molecular weight (MW). The 'high MW' inhibitor co-migrated with the proteins, whereas the 'low MW' inhibitor eluted together with tryptophan, xanthine, hypoxanthine, and nicotinamide. Although these substances did not inhibit Cl- channels we tentatively assume that the 'low MW' cytosolic inhibitor may be a heterocyclic aromatic compound. Alternatively, the 'low MW' inhibitor may be a steroid, because aldosterone has a similar retention time on Superose 12. We can as yet exclude a number of putative cytosolic Cl- channel inhibitors including glutathione, cAMP, cGMP, ATP, GTP, NADH, NADPH, and arachidonic acid.