Effects of ouabain and ortho vanadate on transport‐related properties of the LLC‐PK1 renal epithelial cell line

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Abstract
Uptake of α‐methyl‐D‐glucoside (AMG) by LLC‐PK1 cells is inhibited by the uncoupler p‐trifluoro‐methoxyphenyl‐hydrazone (FCCP) and by the absence of extracellular Na+, indicating that the transport system is energy‐ and Na+ ‐dependent. We have previously demonstrated that transport of AMG by LLC‐PK1 cells proceeds against a concentration gradient and is phlorizin‐sensitive (Mullin et al., '80). Uptake of AMG was also inhibited by ouabain (OUA) but not by ortho‐vanadate (VAN). Rubidium uptake also was affected by OUA but not by VAN. VAN, however, caused collapse of the three‐dimensional domes of confluent LLC‐PK1 monolayers much more rapidly and thoroughly than OUA. Since domes are presumably dependent upon the Na+ pump, yet VAN is not acting on transport‐related functions of the OUA‐sensitive (Na+ + K+)‐ATPase, we hypothesize a direct effect of VAN on the water permeability of these cells. We also suggest that OUA does not act on these cells until domes collapse in normal course, and access of the OUA to the extracellular surface of antiluminal membranes is then achieved.