Biophysical Society Conference | Tahoe 2023

Proton Reactions: From Basic Science to Biomedical Applications

Wednesday Speaker Abstracts

PROTONS IN REPRODUCTION, CONTRACEPTION, AND HEAT PRODUCTION Polina Lishko University of California, Berkley, USA No Abstract

THE ROLE OF NH 3 IN PROMOTING H

+ /OH – FLUX THROUGH THE ALKALI

ACTIVATED CHANNEL PROTEIN SLC4A11 Bianca N Quade 1 ; Aniko Marshall 1 ; Mark D. Parker 1 ; 1 Jacobs School of Medicine, University at Buffalo, Physiology and Biophysics, Buffalo, NY, USA SLC4A11 is the only member of the SLC4 solute carrier family that does not transport HCO 3 – . While most investigators agree that SLC4A11 conducts H + (or the thermodynamically equivalent OH – ), controversy surrounds the mechanism of transport. Indirect evidence suggests that SLC4A11 is capable of NH 3 /H + cotransport. However, our observation that SLC4A11 has an NH 3 -independent H + conductance (G H ) of similar magnitude when intracellular pH (pH i ) is raised, led us to reinterpret those data in favor of a model whereby the stimulatory effect of NH 3 is explained by its alkalinizing influence on pH i . In more recent studies we defined pK i for the pH i -dependence of the NH 3 -independent G H . With this finer appreciation of SLC4A11 activation, we revisited the stimulatory role of NH 3 by overexpressing human SLC4A11 in Xenopus oocytes and determining the relationship between pH i (with a H + -selective microelectrode) and G H (using voltage-clamp circuitry) with 0, 0.5 or 5mM NH 3 . If the NH 3 stimulation of G H is purely mediated by changes in pH i , the addition of NH 3 ought not alter pK i , just increase G H in accordance with the described relationship between pH i and G H . Contrary to this model, our preliminary experiments reveal that the rise in G H caused by NH 3 results from an acidic shift in pK i , with 5mM causing a greater shift in pK i than 0.5mM. These data are consistent with a revised model in which NH 3 is a direct allosteric activator of SLC4A11. SLC4A11 is expressed in corneal endothelial cells in which it supports the fluid pumping function that maintains corneal clarity. As the fluid pump is energized by glutaminolysis, which generates NH 3 , it is possible that such allosteric regulation enables SLC4A11 to alter G H in accordance with the needs of the system.

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