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Regulation of Intracellular pH in Rat Lactotrophs: Involvement of Anionic Exchangers¹

Departement de Fisiologia, Facultad de Salud, Universidad del Valle (L.G.), AA 25 360 Cali, Columbia; and CNRS UMR 5543, Université Victor Segalen Bordeaux 2 (E.B.-G., M.G., P.S.), 33076 Bordeaux, France

Address all correspondence and requests for reprints to: Dr. P. Sartor, CNRS UMR 5543, Université Victor Segalen Bordeaux 2, 146 rue Léo Saignat, 33076 Bordeaux Cedex, France. E-mail: bdneuro{at}umr5543.u-bordeaux2.fr

Regulation of the intracellular pH (pHi) of normal rat lactotrophs was studied. As this cell type, cultured with 10% FCS, can achieve a relatively alkaline pHi (7.3–7.5), we investigated the presence of a mechanism based on Cl^-/HCO₃^- exchange. Using the pHi-sensitive probe SNARF-1 (seminaphtorodafluor) in its permeant form, SNARF-1/AM, we studied pHi recovery after acidic loading in individual cells with a microspectrofluorometric approach. We showed the involvement of anionic exchange in lactotroph cell pHi regulation. Acute CO₂-bicarbonate cell acidic loading combined with external Cl^- depletion induces the activation of a Cl^-/HCO₃^- exchange. This exchange is 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid sensitive and corresponds to the type 3 anionic exchanger (AE3). However, after nigericin acidification, Na⁺/H⁺ exchange can also participate in recovery. In addition, incubation experiments strongly suggest that a 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-insensitive anionic exchanger (type 2 anionic exchanger or AE2) is present in rat lactotrophs. The presence and involvement of carbonic anhydrase in pHi regulation have been demonstrated. Finally, using Northern blot and reverse transcription-PCR techniques, messenger RNAs for both AE2 and AE3 were identified in anterior pituitary cell extracts. We concluded that in normal rat lactotrophs, pHi regulation is achieved by a complex system in which Cl^-/HCO₃^- exchange has a pivotal role.

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