A ROLE FOR NA K ADENOSINE-TRIPHOSPHATASE IN THE PATHOGENESIS OF CYST FORMATION IN EXPERIMENTAL POLYCYSTIC KIDNEY-DISEASE/

Multiple cyst formation with fluid retention is a characteristic struc tural abnormality in polycystic kidney disease (PKD). Na/K adenosine t riphosphatase (ATPase) is a major transporting membrane protein that i s ubiquitous in the epithelial cell, which has been thought to be invo lved in cystogenesis. We have investigated the molecular and histologi c basis of Na/K ATPase activity in experimental PKD in vivo. Rats were treated with diphenylthiazole (100 mg/100 gm body weight), and cyst f ormation was examined histologically. Na/K ATPase activity was measure d enzymatically by using a fluorometric method, and reverse transcript ion-competitive polymerase chain reaction (RT-PCR) analysis was used t o quantitate mRNA levels in the isolated single nephron segment. Kidne ys were immunostained with subunit-specific antibodies to determine th e localization of Na/K ATPase in the epithelial cell. The enzyme activ ity increased in the cortical collecting duct from 25.9 +/- 3.5 mmol/L pmol/mm/min to 72.9 +/- 6.8 pmol/mm/min and in the outer medullary col lecting duct from 13.0 +/- 3.9 mmol/Lpmol/mm/min to 58.5 +/- 9.8 pmol/ mm/min (n = 6, p < 0.01); however, all other segments showed no signif icant changes. No significant alternation in (alpha 1- and beta 1-subu nits of Na/K ATPase mRNA levels was observed by competitive PCR assay in either segment. The enzyme was stained at the basolateral membrane even in the cystic tubules. Na/K ATPase activity was up-regulated in t he cyst-formed kidney, but this was not accompanied with transcription al up-regulation. Increased Na/K ATPase activity at normal locations m ay play a role in abnormal net fluid transport in the development and progression of experimental PKD.