HYPEROXIA INDUCES ALKALINIZATION AND DOME FORMATION IN MDCK EPITHELIAL-CELLS

We observed that confluent Madin-Darby canine kidney (MDCK) epithelial cells exposed to 95% O2 showed intensive dome formation, a manifestation of cell differentiation and transepithelial fluid transport, whereas cells exposed to 40% O2 or to normoxia did not. Hyperoxia-induced dome formation (HIDF) was preceded and accompanied by a significant rise in intracellular pH (pH(i)) on days 2(7.53 vs. 7.42) and 3 (7.62 vs. 7.45), as compared with controls. Inhibition of the Na+-H+ exchanger by 0.1 or 1.0 mM amiloride caused 29 or 69% reduction of HIDF and completely abolished hyperoxia-induced alkalinization of the cells. HIDF was altered by modification of extracellular pH (pH0); there was a decrease by 84% with pH0 6.8, while pH0 7.8 led to earlier and more intensive dome formation (day 2, +472%; day 3, +27%). We also found that adenosine 3',5-cyclic monophosphate (cAMP) was increased in hyperoxic cells, a change that was independent from the rise of pH(i). We conclude that high-level hyperoxia induces dome formation in MDCK epithelial monolayers by a process involving activation of the Na+-H+ exchanger, together with increased intracellular cAMP.