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A novel method to determine the diffusional water permeability of oocyte plasma membranes
Author(s) -
Iserovich Pavel,
Kuang Kunyan,
Chun Terry,
Fischbarg Jorge
Publication year - 1997
Publication title -
biology of the cell
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.543
H-Index - 85
eISSN - 1768-322X
pISSN - 0248-4900
DOI - 10.1111/j.1768-322x.1997.tb01025.x
Subject(s) - membrane , oocyte , biophysics , biology , xenopus , distilled water , tritiated water , chromatography , permeability (electromagnetism) , lipid bilayer , biochemistry , chemistry , microbiology and biotechnology , tritium , embryo , physics , gene , nuclear physics
Measurements of the cell membrane diffusional water permeability (P d ) are important to characterize water passage across water channels and across the lipid bilayer component of the membrane. Existing methods for those measurements are involved; however, we report here a simple procedure to estimate P d in Xenopus laevis oocytes and similar large cells. Due to the different densities of H 2 O and D 2 O (heavy water), an oocyte transferred from normal medium to a D 2 O‐based medium floats initially, but subsequently sinks when a certain amount of the water originally in them is replaced by the D 2 O that diffuses in. We describe how the ‘flotation time’ (time that oocytes float in a heavy water solution before they start sinking) yields the P d of the plasma membrane. Determination of P d by this procedure and by the rate of tritiated water (T 2 O) efflux give for P d results which are very close: 2.2 ± 0.2 (n = 8) and 2.0 ± 0.1 (n = 6) μm/s, respectively (T = 10°C). Further‐more, our method detects the increase in P d elicited in oocytes by either expression of water channel proteins, or by treating them with the pore‐forming antibiotic amphotericin B. This method appears useful to gauge the expression and function of pore‐forming, water‐permeable membrane proteins.