I am interested in the molecular physiology of salt and solute transport, and have exploited genomic databases to identify novel members of four transporter gene families. My laboratory has thus cloned several new members of the cation-chloride cotransporter gene family (1), including the novel K-Cl cotransporters KCC3 and KCC4 (2, 3), human KCC2 (4), and SLC12A9, a new family member with a novel membrane topology. We recently characterized five new members of the SLC26 gene family; these include SLC26A6 (5), a multifunctional transporter that is the primary candidate for both the apical chloride-formate/oxalate exchanger in the renal proximal tubule and the CFTR-dependent chloride-bicarbonate exchanger in the pancreas, and SLC26A9, a lung-specific Cl-base exchanger (6). Apical chloride-formate/oxalate/base exchange mediated by SLC26A6 and basolateral K-Cl cotransport mediated by KCC3 and KCC4 appear to play crucial roles in trans-epithelial salt transport by the proximal tubule (7, 8). Basolateral and apical oxalate exchange in the proximal tubule, mediated by Slc26a1 and Slc26a6 (5), respectively, may also play a significant role in renal oxalate secretion.

The transport function of cloned transporters is primarily studied by isotopic flux measurements, using heterologous expression in Xenopus laevis oocytes. In addition, the electrogenic properties of at least some of the SLC26 exchangers and other transporters leave them amenable to electrophysiological analysis. Isoform-specific functional properties provide a starting point for structure-function analysis, using chimeric and mutant cDNAs. Immunolocalization of transporter transcripts and proteins has also provided important information on physiological roles in the kidney (8) and brain (9), which have guided the physiological characterization of the relevant knockout mice (10). Finally, collaborative investigations are addressing the role of multiple human transporters in both monogenic and polygenic disease.

References:

1. Delpire, E., and Mount, D.B. 2002. Human and murine phenotypes associated with defects in cation-chloride cotransport. Annu Rev Physiol 64:803-843.
2. Mount, D.B., Mercado, A., Song, L., Xu, J., George, A.L., Jr., Delpire, E., and Gamba, G. 1999. Cloning and characterization of KCC3 and KCC4, new members of the cation-chloride cotransporter gene family. J Biol Chem 274:16355-16362.
3. Mercado, A., Song, L., Vazquez, N., Mount, D.B., and Gamba, G. 2000. Functional Comparison of the K+-Cl- Cotransporters KCC1 and KCC4. J Biol Chem 275:30326-30334.
4. Song, L., Mercado, A., Desai, R., George, A.L.J., Gamba, G., and Mount, D.B. 2002. Molecular, Functional, and Genomic Characterization of Human KCC2, the Neuronal K-Cl Cotransporter. Molecular Brain Research 103:91-105.
5. Xie, Q., Welch, R., Mercado, A., Romero, M.F., and Mount, D.B. 2002. Molecular characterization of the murine Slc26a6 anion exchanger, functional comparison to Slc26a1. Am J Physiol in press.
6. Xie, Q., Welch, R., Song, L., Romero, M.F., and Mount, D.B. 2002. Cloning and characterization of four novel Slc26 anion exchangers. J Biol Chem in revision.
7. Mount, D.B., and Gamba, G. 2001. Renal K-Cl cotransporters. Curr Opin Nephrol Hypertens 10:685-692.
8. Mount, D.B., Song, L., Mercado, A., Gamba, G., and Delpire, E. 2000. Basolateral localization of renal tubular K-Cl cotransporters. J. Am. Soc. Nephrol. 11:35A.
9. Pearson, M.M., Lu, J., Mount, D.B., and Delpire, E. 2001. Localization of the K(+)-Cl(-) cotransporter, KCC3, in the central and peripheral nervous systems: expression in the choroid plexus, large neurons and white matter tracts. Neuroscience 103:481-491.
10. Delpire, E., Mount, D.B., Lu, J., England, R., Kirby, M., and McDonald, M.P. 2001. Locomotor defects associated with disruption of the K-Cl cotransporter KCC3. FASEB Journal 15:A440.

 

Lab Personnel:

Adriana Mercado, Ph.D.
Kambiz Zandi-Nejad, M.D.

 

Harvard Institutes of Medicine

email contact: lalice@rics.bwh.harvard.edu

phone contact: (617) 525-5828