Evidence from simultaneous intracellular- and surface-pH transients that carbonic anhydrase II enhances CO₂ fluxes across Xenopus oocyte plasma membranes

Abstract

Musa-Aziz R, Occhipinti R, Boron WF. Evidence from simultaneous intracellular-and surface-pH transients that carbonic anhydrase II enhances CO2 fluxes across Xenopus oocyte plasma membranes.

Evidence from mathematical modeling that carbonic anhydrase II and IV enhance CO2 fluxes across Xenopus oocyte plasma membranes

“…Thus, such an oocyte would have been injected with Tris (rather than CA II ϩ Tris) in the first paper in this series (14) or H 2 O (rather than cRNA encoding CA IV ϩ H 2 O) in the second paper (15). In our numerical experiments, we will not distinguish between Tris-and H 2 O-injected oocytes.…”

“…2 are not significantly different between the two types of oocytes. For consistency, we will use the physiological data from Tris oocytes, from the first paper (14), to set up the properties of our in silico "control" oocyte in all of our simulations.…”

“…The model confirms the hypothesis that CA II and CA IV enhance transmembrane CO2 fluxes by maximizing CO2 gradients across the plasma membrane, and it predicts that the pH effects of simultaneously implementing intracellular and extracellular-surface CA are supra-additive. reaction-diffusion; tortuosity factors; intracellular pH; surface pH; competing equilibria; buffers IN THE TWO COMPANION PAPERS, we studied the effects of the cytosolic enzyme carbonic anhydrase II (CA II) and of the GPI-linked extracellular CA IV on enhancing CO 2 fluxes across the plasma membrane (14,15). We assessed these fluxes by using pH microelectrodes to measure simultaneously intracellular (pH i ) and surface pH (pH S ) as we added or removed extracellular CO 2 /HCO 3 Ϫ .…”

“…In the preceding two papers, we used mathematical simulations to help us understand how CA II (14) or CA IV (15) influences CO 2 -induced pH i and pH S transients when we alter the experimental protocol. These protocol changes included raising levels of CO 2 in the bulk extracellular fluid (BECF), increasing the depth of penetration of the pH i microelectrode, and varying the concentration of the extracellular HEPES buffer.…”

How carbonic anhydrases and pH buffers facilitate the movement of carbon dioxide through biological membranes. Focus on “Evidence from simultaneous intracellular- and surface-pH transients that carbonic anhydrase II enhances CO2 fluxes across Xenopus oocyte plasma membranes”; “Evidence from simultaneous intracellular- and surface-pH transients that carbonic anhydrase IV enhances CO2 fluxes across Xenopus oocyte plasma membranes”; and “Evidence from mathematical mo

“…They then applied 1.5% CO 2 /10 mM HCO 3 Ϫ and followed both surface and intracellular pH changes (5). Cytosolic CA II sped up the conversion of incoming CO 2 to HCO 3 Ϫ and H ϩ , thereby maintaining a low intracellular [CO 2 ], and thus promoting CO 2 influx.…”