The transmembrane transport of bicarbonate is a key step in many important biological processes, and problems with bicarbonate transport are at the origin of various diseases. This warrants efforts to develop synthetic transporters for bicarbonate. However, the mechanisms of bicarbonate transport by synthetic receptors are not fully understood and reliable assays to report on bicarbonate directly are needed. We present an assay that allows the kinetics of bicarbonate transport into liposomes to be monitored directly, using fluorescence spectroscopy (Figure 1). Our assay offers a number of advantages over existing methodologies including a real-time read-out signal and high sensitivity. These enable the mechanisms of bicarbonate transport to be determined, various antiport and uniport processes to be compared, and low concentrations of anionophores to be used. We have found that mechanisms involving CO2 diffusion and the dissipation of a pH gradient can lead to an increase in bicarbonate concentration within liposomes, without transport of the anion occurring at all. This potential mechanism should be considered when developing and studying bicarbonate transporters for applications in physiological studies or therapies, and the assay presented here can be used to distinguish this alternative mechanism from actual bicarbonate transport.

Direct monitoring of bicarbonate transport by fluorescence spectroscopy

ACS Spring Meeting 2021

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