Bestrophin-2 mediates bicarbonate transport by goblet cells in mouse colon
Kuai Yu, Rafael Lujan, Alan Marmorstein, Sherif Gabriel, H. Criss Hartzell
Kuai Yu, Rafael Lujan, Alan Marmorstein, Sherif Gabriel, H. Criss Hartzell
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Research Article Gastroenterology

Bestrophin-2 mediates bicarbonate transport by goblet cells in mouse colon

Abstract

Anion transport by the colonic mucosa maintains the hydration and pH of the colonic lumen, and its disruption causes a variety of diarrheal diseases. Cholinergic agonists raise cytosolic Ca2+ levels and stimulate anion secretion, but the mechanisms underlying this effect remain unclear. Cholinergic stimulation of anion secretion may occur via activation of Ca2+-activated Cl– channels (CaCCs) or an increase in the Cl– driving force through CFTR after activation of Ca2+-dependent K+ channels. Here we investigated the role of a candidate CaCC protein, bestrophin-2 (Best2), using Best2–/– mice. Cholinergic stimulation of anion current was greatly reduced in Best2–/– mice, consistent with our proposed role for Best2 as a CaCC. However, immunostaining revealed Best2 localized to the basolateral membrane of mucin-secreting colonic goblet cells, not the apical membrane of Cl–-secreting enterocytes. In addition, in the absence of HCO3–, cholinergic-activated current was identical in control and Best2–/– tissue preparations, which suggests that most of the Best2 current was carried by HCO3–. These data delineate an alternative model of cholinergic regulation of colonic anion secretion in which goblet cells play a critical role in HCO3– homeostasis. We therefore propose that Best2 is a HCO3– channel that works in concert with a Cl:HCO3– exchanger in the apical membrane to affect transcellular HCO3– transport. Furthermore, previous models implicating CFTR in cholinergic Cl– secretion may be explained by substantial downregulation of Best2 in Cftr–/– mice.

Authors

Kuai Yu, Rafael Lujan, Alan Marmorstein, Sherif Gabriel, H. Criss Hartzell

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Figure 5

Best2 expression in colon from Cftr–/– mice.

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Best2 expression in colon from Cftr–/– mice. (A) Isc from Cftr–/– an...
(A) Isc from Cftr–/– and WT mice, recorded as in Figure 4. Shown are results with normal Krebs and HCO3–-free solutions as well as the difference between them. n = 5 mucosal samples from 2 WT mice; n = 9 mucosal samples from 4 Cftr–/– mice. P < 0.01, all Cftr–/– versus all respective WT values. (B) Western blot of Best2 expression in WT (WT1 and WT2) and Cftr–/– (CF1–CF4) colon samples. Samples were the same ones used for Isc measurements in A. Blots were stained with Best2 (58 kDa) and GAPDH (37 kDa) antibodies. (C–H) Immunofluorescence of WT (C and D) and Cftr–/– (E–H) colon samples. Samples are adjacent tissue from the same colons used for Isc measurements in A. Arrowheads in E and F indicate interstitial accumulation of Best2 staining; asterisks in D, F, and H are shown for comparison of Best2 staining in the cytoplasm for comparison. Scale bars: 20 μm (C, E, and G); 10 μm (D, F, and H).