Prostaglandins may mediate chloride concentration gradient across domes formed by MDCK₁ cells

The MDCK₁ and LLC-PK₁ cell lines have been used to characterize transepithelial transport in isolated culture. Both can be maintained in continuous culture and form domes that represent fluid actively transported from luminal to contraluminal surface. Fluid in domes from LLC-PK₁ cells was isotonic with the culture medium and no Cl gradient between domes and medium was present. Fluid from domes formed by MDCK₁ cells was also isotonic with respect to Na and K but there was a persistent Cl concentration gradient. To evaluate prostaglandin (PG) production by these cell lines, the culture medium was analyzed for PGE. LLC-PK₁ cells released no measurable PGE; MDCK₁ cells regularly released PGE both during basal conditions and after augmentation of PG synthesis by a high Ca concentration in the medium. Qualitatively similar results had previously been found with these cell lines when PG synthesis was augmented with addition of arachidonic acid or Ca ionophore A23187, and PGE or 6-keto-prostaglandin F(1α) was measured in the medium. To evaluate whether PGs might be responsible for the Cl gradient across MDCK₁ cells, indomethacin or meclofenamate was added. There was a marked decrease in the Cl gradient with either agent at 5 h. To evaluate the possibility that PGE₂ or PGI₂ plays a role in maintaining this Cl gradient, further studies were done in which indomethacin was added to the culture medium to block endogenous PG synthesis, and exogenous PGE₂ or PGI₂ was added. Although addition of PGE₂ was without effect, addition of PGI₂ to indomethacin-treated cells maintained the Cl gradient for at least 5 h. Thus LLC-PK₁ cells neither produce PGs nor generate a Cl gradient but MDCK₁ cells do both. These findings, together with the findings that indomethacin and meclofenamate diminish the Cl gradient across MDCK₁ cells and PGI₂ can maintain it when indomethacin is added, suggest that the Cl gradient may be, in part, PG (and possibly PGI₂) mediated.