Bicarbonate exchange through the human red cell membrane determined with [14C] bicarbonate

Area of Science:

• Biochemistry
• Cell Biology
• Physiology

Background:

• Red blood cell membranes facilitate ion transport, crucial for physiological processes.
• Understanding bicarbonate transport is key to comprehending acid-base balance and gas exchange.

Purpose of the Study:

• To investigate the mechanism and kinetics of bicarbonate transport across human red cell membranes.
• To compare bicarbonate transport with chloride self-exchange.

Main Methods:

• Studied 14C-labelled bicarbonate efflux from resealed erythrocyte ghosts at low temperatures (0-10°C).
• Utilized carbonic anhydrase inhibitors to eliminate CO2 as a confounding factor.
• Employed the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS) to assess inhibition kinetics.

Main Results:

• Bicarbonate self-exchange is a saturable function, with maximal flux at ~100 mM and half-maximal flux at 10 mM.
• Inhibitors like DIDS demonstrated that bicarbonate transport is mediated by the inorganic anion exchanger.
• Maximum bicarbonate exchange flux was ~30% higher than chloride, with about three times greater affinity for the transport site.

Conclusions:

• Bicarbonate is transported via the erythrocyte's inorganic anion exchange mechanism, similar to chloride.
• Differences in exchange kinetics are attributed to varying affinities of bicarbonate and chloride for the transporter's binding sites.
• The findings clarify the role of the anion exchanger in red blood cell physiology.