Acidification slows the transport but does not influence the polarity of secretion of gp80 in the polarized epithelial cell MDCK.

Madin-Darby canine kidney (MDCK) cells stably transfected with a recombinant chicken lysozyme gene were used to examine the effect of cytoplasmic acidification on the secretion of the endogenous gp80 glycoprotein complex and lysozyme. The effect was examined by pulse-chase and immunofluorescence analysis. If filter-grown monolayers were incubated at pH 5.8 the secretion of gp80 was retarded, and the transport of lysozyme was completely inhibited. The immunofluorescence analysis revealed an enrichment of both proteins in the endoplasmic reticulum. The transport block was reversible for both proteins upon transferring the filter-grown monolayer back into medium at pH 7.4.