title: SLC4A11 is an EIPA-sensitive Na(+) permeable pHi regulator.
abstract: Slc4a11, a member of the solute linked cotransporter 4 family that is comprised predominantly of bicarbonate transporters, was described as an electrogenic 2Na(+)-B(OH)4(-) (borate) cotransporter and a Na(+)-2OH(-) cotransporter. The goal of the current study was to confirm and/or clarify the function of SLC4A11. In HEK293 cells transfected with SLC4A11 we tested if SLC4A11 is a: 1) Na(+)-HCO3(-) cotransporter, 2) Na(+)-OH(-)(H(+)) transporter, and/or 3) Na(+)-B(OH)4(-) cotransporter. CO2/HCO3(-) perfusion yielded no significant differences in rate or extent of pHi changes or Na(+) flux in SLC4A11-transfected compared with control cells. Similarly, in CO2/HCO3(-), acidification on removal of Na(+) and alkalinization on Na(+) add back were not significantly different between control and transfected indicating that SLC4A11 does not have Na(+)-HCO3(-) cotransport activity. In the absence of CO2/HCO3(-), SLC4A11-transfected cells showed higher resting intracelllular Na(+) concentration ([Na(+)]i; 25 vs. 17 mM), increased NH4(+)-induced acidification and increased acid recovery rate (160%) after an NH4 pulse. Na(+) efflux and influx were faster (80%) following Na(+) removal and add back, respectively, indicative of Na(+)-OH(-)(H(+)) transport by SLC4A11. The increased alkalinization recovery was confirmed in NHE-deficient PS120 cells demonstrating that SLC4A11 is a bonafide Na(+)-OH(-)(H(+)) transporter and not an activator of NHEs. SLC4A11-mediated H(+) efflux is inhibited by 5-(N-ethyl-N-isopropyl) amiloride (EIPA; EC50: 0.1 μM). The presence of 10 mM borate did not alter dpHi/dt or ΔpH during a Na(+)-free pulse in SLC4A11-transfected cells. In summary our results show that SLC4A11 is not a bicarbonate or borate-linked transporter but has significant EIPA-sensitive Na(+)-OH(-)(H(+)) and NH4(+) permeability.
authors.affiliation: School of Optometry, Indiana University, Bloomington, Indiana;
authors.forename: Diego G
authors.initials: DG
authors.lastname: Ogando
authors.forename: Supriya S
authors.initials: SS
authors.lastname: Jalimarada
authors.forename: Wenlin
authors.initials: W
authors.lastname: Zhang
authors.forename: Eranga N
authors.initials: EN
authors.lastname: Vithana
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Bonanno
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000595:Amino Acid Sequence; D000643:Ammonium Chloride / Q000378:metabolism; D000818:Animals; D027321:Anion Transport Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D017920:Antiporters / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D016466:CHO Cells; D002463:Cell Membrane Permeability / Q000187:drug effects*; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D062686:Epithelial Sodium Channel Blockers / Q000494:pharmacology*; D057809:HEK293 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D008969:Molecular Sequence Data; D012964:Sodium / Q000378:metabolism*; D012972:Sodium Hydroxide / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
chemical_list: D027321:Anion Transport Proteins; D017920:Antiporters; D062686:Epithelial Sodium Channel Blockers; C425809:SLC4A11 protein, human; D000643:Ammonium Chloride; D012972:Sodium Hydroxide; D000584:Amiloride; D012964:Sodium; C039614:ethylisopropylamiloride
keywords: Na+ permeability; SLC4A11; bicarbonate; borate; pH