EVIDENCE FOR THE PRESENCE OF A HG-INHIBITABLE WATER-PERMEABILITY PATHWAY AND AQUAPORIN-1 IN A5 SALIVARY EPITHELIAL-CELLS

The molecular basis of water-permeability in salivary and other exocri ne glands is not understood. We have examined two well-studied salivar y epithelial cell lines for evidence of a Hg-inhibitable water-permeab ility pathway. A5 and HSG cells are derived from rat and human submand ibular glands, respectively. Only A5 cells demonstrated such a pathway . The rate of A5 cell osmotic shrinkage was inhibited about fivefold i n the presence of 300 mu M HgCl2. To determine if this activity was as sociated with the expression of the prototypical water channel (aquapo rin, AQP) AQP1, we used three separate experimental approaches; Northe rn analysis and reverse transcription-polymerase chain reaction (RT-PC R) analysis of isolated mRNA, and Western analysis of cell membranes. All three methods yielded positive results with A5 cells and negative results with HSG cells. The similar to 800 bp product of RT-PCR was an alyzed further by sequencing and restriction enzyme digestion. The res ults were consistent with the previously reported coding region sequen ce for rat kidney AQP1. The aggregate data demonstrate that marked dif ferences in water-permeability and water channel expression exist in t hese two salivary epithelial cell lines. (C) 1995 Wiley-Liss, Inc.