Boric acid transport activity of human aquaporins expressed in Xenopus oocytes

Abstract

Boron is an essential element in various organisms. The biological importance of boron was initially described in plants (Tanaka & Fujiwara, 2008;Warington, 1923). Boron deficiency influences the growth and expansion of plant organs, such as leaves, roots, flowers, fruits, and seeds, and boron availability is widely recognized as an

Boric acid transport activity of marine teleost aquaporins expressed in Xenopus oocytes

“…TrAqp, Takifugu rubripes aquaporin; HsAqp, Homo sapiens aquaporin. Results of HsAqps were recalculated from our previous study (Ushio et al, 2022 ). Control 1 and 2 indicate results of water‐injected oocytes in this and the previous study, respectively.…”

“…Boric acid (B(OH) 3 ) is in equilibrium with borate (B(OH) 4 − ) in aqueous solutions. To determine which form is transported in oocytes expressing TrAqps, B(OH) 3 or B(OH) 4 − , we analyzed changes in intracellular pH (pH i ) of oocytes expressing TrAqps in a solution containing boric acid because B(OH) 3 influx elicits intracellular acidification, but the influx of B(OH) 4 − elicits intracellular alkalization and membrane hyperpolarization (Kato et al, 2022 ; Ushio et al, 2022 ). Changes in pH i were analyzed in oocytes expressing TrAqp3a, 7, 8bb, 9a, and 9b in an iso‐osmotic solution containing boric acid.…”

“…( A ‐ F ) The average values of water and solute permeabilities ( P water , P glycerol , P urea , and P boric acid , shown in Table 2 ) expressing pufferfish TrAqps are plotted in red, and those of water‐injected oocytes were plotted in gray. The average values of water and solute permeabilities of oocytes expressing human HsAqps were recalculated from our previous study (Ushio et al, 2022 ) (Table 2 ) were plotted as comparison in blue. The correlations ( r ) calculated from the average values of TrAqp and control ( n = 11) were shown with p value in red, and those calculated from the average values of TrAqp, HsAqp, and each control ( n = 21) were shown with p value in black.…”

“…The correlation among the average values of P water, P glycerol , P urea , and P boric acid of TrAqp oocytes was calculated by Pearson's correlation using Excel software (Version 2019, Microsoft). Next, P water , P glycerol , P urea , and P boric acid of oocytes expressing human Aqps (HsAqp1, 2, 3, 4, 5, 7, 8, 9, and 10) and control oocytes were similarly calculated from our previous swelling data (Ushio et al, 2022 ), and the average values were prepared as comparison. The correlation among the average values of P water, P glycerol , P urea , and P boric acid of TrAqp and HsAqp oocytes was again calculated by Pearson's correlation using Excel software.…”

Seawater fish use an electrogenic boric acid transporter, Slc4a11A, for boric acid excretion by the kidney

“…Recently, we analyzed the boric acid transport activity of human AQPs and showed that AQP3, AQP7, AQP8, AQP9, and AQP10 act as boric acid transport systems, likely as B(OH) 3 channels, based on the following evidence: (1) boric acid elicited a marked “decrease” in pH i but did not elicit a change in membrane potential in Xenopus oocytes expressing these AQPs and (2) boric acid altered intracellular boron content in Xenopus oocytes expressing these AQPs ( 63 ). The results showed that the B(OH) 3 transport activities of AQP3, AQP7, AQP8, AQP9, and AQP10 are electroneutral, suitable for the facilitated diffusion of B(OH) 3 across the plasma membrane, and contrast with the electrogenic boric acid transport activity of Slc4a11A.…”