GOLAC: An endogenous anion channel of the Golgi complex

The Golgi complex is present in every eukaryotic cell and functions in post translational modifications and sorting of proteins and lipids to post-Golg i destinations. Both functions require an acidic lumenal pH and transport o f substrates into and by-products out of the Golgi lumen. Endogenous ion ch annels are expected to be important for these features, but none has been d escribed. ion channels from an enriched Golgi fraction cleared of transitin g proteins were incorporated into planar lipid bilayers. Eighty percent of the single-channel recordings revealed the same anion channel. This channel has novel properties and has been named GOLAC (Golgi anion channel). The c hannel has six subconductance states with a maximum conductance of 130 pS, is open over 95% of the time, and is not voltage-gated. Significant for Gol gi function, the channel conductance is increased by reduction of pH on the lumenal surface. This channel may serve two nonexclusive functions: provid ing counterions for the acidification of the Golgi lumen by the H+-ATPase a nd removal of inorganic phosphate generated by glycosylation and sulfation of proteins and lipids in the Golgi.