The Journal of General Physiology
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Published online
doi:10.1085/jgp.200810097
The Journal of General Physiology, Vol. 133, No. 4, 421-438
The Rockefeller University Press, 0022-1295 $30.00
© Bertrand et al.
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ARTICLE

 SLC26A9 is a constitutively active, CFTR-regulated anion conductance in human bronchial epithelia

Carol A. Bertrand1, Ruilin Zhang1, Joseph M. Pilewski2, and Raymond A. Frizzell1

1 Department of Cell Biology and Physiology, and 2 Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261

Correspondence to Carol A. Bertrand: cbertra{at}pitt.edu

Human bronchial epithelial (HBE) cells exhibit constitutive anion secretion that is absent in cells from cystic fibrosis (CF) patients. The identity of this conductance is unknown, but SLC26A9, a member of the SLC26 family of CF transmembrane conductance regulator (CFTR)-interacting transporters, is found in the human airway and exhibits chloride channel behavior. We sought differences in the properties of SLC26A9 and CFTR expressed in HEK 293 (HEK) cells as a fingerprint to identify HBE apical anion conductances. HEK cells expressing SLC26A9 displayed a constitutive chloride current that was inhibited by the CFTR blocker GlyH-101 (71 ± 4%, 50 µM) and exhibited a near-linear current–voltage (I-V) relation during block, while GlyH-101–inhibited wild-type (wt)CFTR exhibited a strong inward-rectified (IR) I-V relation. We tested polarized HBE cells endogenously expressing either wt or {Delta}F508-CFTR for similar activity. After electrical isolation of the apical membrane using basolateral {alpha}-toxin permeabilization, wtCFTR monolayers displayed constitutive chloride currents that were inhibited by GlyH-101 (68 ± 6%) while maintaining a near-linear I-V relation. In the absence of blocker, the addition of forskolin stimulated a current increase having a linear I-V; GlyH-101 blocked 69 ± 7% of the current and shifted the I-V relation IR, consistent with CFTR activation. HEK cells coexpressing SLC26A9 and wtCFTR displayed similar properties, as well as forskolin-stimulated currents that exceeded the sum of those in cells separately expressing SLC26A9 or wtCFTR, and an I-V relation during GlyH-101 inhibition that was moderately IR, indicating that SLC26A9 contributed to the stimulated current. HBE cells from CF patients expressed SLC26A9 mRNA, but no constitutive chloride currents. HEK cells coexpressing SLC26A9 with {Delta}F508-CFTR also failed to exhibit SLC26A9 current. We conclude that SLC26A9 functions as an anion conductance in the apical membranes of HBE cells, it contributes to transepithelial chloride currents under basal and cAMP/protein kinase A–stimulated conditions, and its activity in HBE cells requires functional CFTR.

Abbreviations used in this paper: ASL, airway surface liquid; CF, cystic fibrosis; DIDS, 4,4'-diisothiocyanatostilbene-2,2' disulfonic acid; GFP, green fluorescent protein; HBE, human bronchial epithelial; Im, membrane current; IP, immunoprecipitation; IR, inward-rectified/rectification; OR, outward-rectified/rectification; RIV, I-V ratio; Rm, membrane resistance; RP, reverse transcriptase; wt, wild-type.

©2009 Bertrand et al.
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