EXPRESSION OF AQUAPORINS IN XENOPUS-LAEVIS OOCYTES AND GLIAL-CELLS ASDETECTED BY DIFFUSION-WEIGHTED H-1-NMR SPECTROSCOPY AND PHOTOMETRIC SWELLING ASSAY

Expression of aquaporins (AQP) and water permeability were studied in Xenopus laevis oocytes and immobilized glial cells by a pulsed-field g radient spin echo NMR technique and a photometric swelling assay. Oocy tes injected with poly(A) RNA from C6-BU-1 cells showed increased swel ling behavior under hypoosmotic stress due to expressed ater channels as compared to control oocytes. The swelling could be reversibly inhib ited by HgCl2. Furthermore, the intracellular relaxation time and the apparent intracellular diffusion coefficient of water in oocytes were determined by diffusion-weighted H-1 NMR experiments to be T-2 = 36 ms and D-app,D-intra = 0.18 X 10(-3) mm(2)/s. Ln immobilized C6 and F98 cells the mean exchange time of intracellular water was found to be 51 ms which increased to 75 ms upon chronic treatment (4 days) in hypert onic medium. Additional hybrid depletion experiments with antisense ol igonucleotides directed against AQP1 were performed on oocytes and C6 cells. Moreover, different water channel subtypes of glial cells were assessed by a reverse transcriptase polymerase chain reaction assay. W ith this, the mRNA encoding AQP1 could be detected in primary cultures and glial cell lines, whereas AQP4 mRNA was found in astroglia-rich p rimary cultures, but not in F98 and C6 cells. Our results show that wa ter permeability in glial cells is mainly mediated by water channels w hich play an important role in the regulation of water flow in brain u nder normal and pathological conditions. (C) 1998 Elsevier Science B.V . All rights reserved.