Water permeability changes of FaPIP2;1-expressing oocytes triggered by different osmotic gradients: evidence in favor of mechanical regulation

ACUÑA, CYNTHIA FLORENCIA; GALIZIA, LUCIANO; GUASTAFERRI, FLORENCIA V.; BRACAMONTE, M. VICTORIA; SUTKA, MOIRA; OZU, MARCELO

La Plata

Congreso; XLVII Annual Meeting SAB; 2018

Sociedad Argentina de Biofísica

Our previous works demonstrated that: 1) human AQP1 (HsAQP1) and BvTIP1;2 from beet are aquaporins characterized by a non-linear relationship between the water flux (Jw) and the osmotic gradient (Dosm); and 2) this is due to the decrease of the osmotic permeability coefficient (Pf) mediated by membrane tension increments. On the other hand, BvPIP2;1 (a PIP member from beet) showed a linear Jw-Dosm relationship, indicating that it is not mechanosensitive. Since PIPs and AQP1 share a common ancestor, we wonder if other PIPs can be mechanosensitive. Therefore, in this work we studied the transport properties of FaPIP2;1 (from strawberry) by injecting different quantities of cRNA in xenopus oocytes. After 48 h of expression, the oocytes were subjected to different Δosm created with mannitol (40, 90 and 140 mOmol.Kgw-1). Oocytes volume changes were registered by videomicroscopy and Jw and Pf were determined from the initial slope of volume kinetics. Controls were performed with water-injected or 100 μM amphotericin-incubated oocytes. While controls show linear Jw-Dosm relationships, FaPIP2;1-expressing oocytes show deviations from linearity, similar to previous reports with HsAQP1 and BvTIP2;1. Oocytes injected with 5 ng of FaPIP2;1-cRNA show a significant decrease (p<0.05) of Pf (cm.s-1) with high osmotic gradients:0.023 ± 0.008 (40 mosmol.Kgw-1, N=3, n=6) vs 0.008 ± 0.001 (140 mosmol.Kgw-1, N=5, n=10). Similar results were observed with 10 and 14 ng. In other experiments, 5ng of FaPIP2;1-cRNA/oocyte were tested without vitelline envelope (VE), observing the same result. In addition, Pf determinations (cm.s-1) with the same gradient (160 mosmol.Kgw-1) in FaPIP2;1 injected-oocytes (5 ng/oocyte) are not dependent on the absence (0.019 ± 0.005, N=1, n=6) or presence (0.017 ± 0.007, N=1, n=3) of the VE. Our results suggest that: 1) FaPIP2;1 responds like mechanosensitive aquaporins do; and 2) the VE could not be involved in the mechanical regulation mechanism.