Process of oocyte isolation. (A) 1. Enzymatic and mechanical dissociation of Lithobates oocytes. First, the ovary fragments were cut into small pieces and treated with Type VII Collagenase (0.25 mg/ml) for 5 min. 2. After this first enzymatic dissociation, healthy stage V-VI oocytes were mechanically isolated with tweezers. (B) Comparison between a defolliculated isolated Lithobates oocyte and a defolliculated isolated Xenopus oocyte. Note: the image of the Xenopus oocyte was adapted from Batra (2016).

Sequence alignment of hAQP1, rAQP3, hAQP7, hAQP8 and rAQP9. The sequence alignment shows the two conserved NPA (asparagine-proline-alanine) motifs (bold), as well as the mercury-sensitive cysteine residues in AQP1 (Cys 189), AQP3 (Cys 11), AQP8 (Cys 202) and AQP9 (Cys 213) (highlighted in gray). Each Cys is located in the mouth of the aquapore, with the exception of the Cys in AQP3 (Cys 11), which is located on the intracellular side of the protein. AQP7 does not have a mercury-sensitive Cys residue, and is not inhibited by mercury.

Surface expression of hAQP1, hAQP1_FLAG, hAQP1_C189S, rAQP3, hAQP7, hAQP8 and rAQP9 versus H₂O-injected control oocytes. The surface expression of hAQP1, hAQP1_C189S mutant, rAQP3, hAQP7, hAQP8 and hAQP9 monomers (∼28 kDa) is shown by immunoreactive bands detected at a molecular weight (MW) between 25 and 37 kDa, using polyclonal antibodies (anti-AQP1, anti-AQP3, anti-AQP7, anti-AQP8 and anti-AQP9, respectively). The surface expression of hAQP1_FLAG monomer is shown by a band at a MW between 25 and 37 kDa, using a monoclonal antibody anti-FLAG. All the western blots show the absence of this immunoreactive bands in the H₂O-injected control oocytes. Oocytes from 8–18 different frogs (i.e. batches of oocytes) were analyzed for surface expression, depending on the AQP construct used.

Time course of cell swelling for hAQP1-expressing oocytes and H₂O-injected controls. (A) The pictures in the upper panel show three H₂O-injected oocytes exposed to a hypotonic ND96 variant solution (∼70 mOsm) over the time course of 5 min, in which they do not show any significant cell swelling. (B) The pictures in the lower panel show three hAQP1-expressing oocytes exposed to the same hypotonic ND96 solution over the time course of 5 min, in which they show a significant cell swelling, as well as cell explosion. Values are means±s.e., with numbers of oocytes in parentheses.

Osmotic water permeability (P_f) values of oocytes expressing hAQP1, hAQP1_C189S, hAQP1_FLAG, rAQP3, hAQP7, hAQP8 and rAQP9 versus their day-matched H₂O-injected control oocytes, before and after the treatment with pCMBS (1 mM for 30 min). The P_f values of AQP-expressing oocytes (black bars) are significantly greater than those of the P_f of day-matched H₂O-injected controls (gray bars) (P<0.0001, t-test). Treatment with pCMBS significantly reduced the P_f of oocytes expressing AQP1 (P=0.002, t-test), AQP1_FLAG (P=0.01, t-test), AQP8 (P=0.007, t-test), and AQP9 (P=0.005, t-test) versus their day-matched H₂O controls, but had no effect on oocytes expressing hAQP1_C189S, rAQP3 and hAQP7 versus their day-matched H₂O controls (P<0.0001, t-test). In addition, a comparison of hAQP1_C189S mutant, rAQP3 and hAQP7 before and after pCMBS treatment was not significant different based on a t-test (P values: 0.86 for hAQP1_C189S, 0.33 for rAQP3 and 0.59 for hAQP7). Oocytes from 8–18 different frogs (i.e. batches of oocytes) were used for calculating the P_f of each AQP.

Channel-dependent osmotic water permeability (P_f*) of oocytes expressing hAQP1, hAQP1_FLAG hAQP1_C189S, rAQP3, hAQP7, hAQP8 and rAQP9 before and after treatment with pCMBS (1 mM for 30 min). Subtracting the P_f value for day-matched H₂O-injected control oocytes from the P_f of each AQP-expressing oocyte, before and after pCMBS treatment yields the channel-dependent osmotic water permeability (P_f*). Treatment with pCMBS reduces the P_f* of hAQP1 (P=0.01, t-test), hAQP1_FLAG (P=0.03, t-test), hAQP8 (P=0.03, t-test) and rAQP9 (P=0.02, t-test), but has no effect on P_f* of hAQP_C189S mutant (P=0.85, t-test), AQP3 (P=0.10, t-test), and AQP7 (P=0.54, t-test). A one-way ANOVA, followed by an SNK post hoc analysis to compare P_f* before and after treatment with pCMBS was also performed. Overall P values: P=0.27 before pCBMS treatment and P=0.0001 after pCMBS treatment).