Water permeability properties of the ovarian oocytes from Bufo arenarum and Xenopus laevis: a comparative study.

The water permeability properties of ovarian oocytes from Xenopus laevis and Bufo arenarum, a toad species found in the Buenos Aires region, were studied. We report that: (i) the water osmotic permeability (Pf, cm/sec x 10(-4)) was significantly higher in Bufo (6 degrees C = 12.3 +/- 2.4; 18 degrees C = 20.8 +/- 4.8) than in Xenopus oocytes (6 degrees C = 5.3 +/- 0.3; 18 degrees C = 6.2 +/- 1.6). The corresponding water diffusion permeability values (Pd, cm/sec x 10(-4)) were: Xenopus = 2.3 +/- 0.3 (6 degrees C) and 4.8 +/- 0.7 (18 degrees C); Bufo = 2.7 +/- 0.4 (6 degrees C) and 6.0 +/- 0.5 (18 degrees C). (ii) Amphotericin B increased the Pf and Pd values. The observed delta Pf/delta Pd ratio was not significantly different from the expected results (n = 3), after amphotericin B incorporation in both species. This means that the influence of unstirred layers and other potential artifactual compounds did not significantly affect our experimental results. (iii) Preincubation with gramicidin during 12 hr induced a clear increase in the oocyte volume. After that, a hypotonic shock only slightly increased the oocyte volume. Conversely, a hypertonic challenge induced a volume change significantly higher than the one observed in control conditions. (iv) Mercury ions did not affect the osmotic permeability in Xenopus oocytes but clearly inhibited, in a reversible way, the osmotic permeability in oocytes from B. arenarum. (v) Mercury ions did not reduce Pd values in either species.(ABSTRACT TRUNCATED AT 250 WORDS)