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Forskolin (cAMP) Promotes Insertion of Large Conductance Potassium (KCa1.1) Channels into Apical Membranes of Rat Distal Colon
Author(s) -
Nickerson Andrew,
Rottgen Trey,
Minor Emily,
Rajendran Vazhaikkurichi M
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.856.17
Subject(s) - forskolin , chemistry , apical membrane , ussing chamber , homeostasis , medicine , endocrinology , bk channel , secretion , amiloride , potassium channel , biophysics , biology , receptor , biochemistry , membrane , sodium , organic chemistry
Mammalian colon contributes significantly to overall K + homeostasis. Under normal conditions, the proximal colon secretes and distal colon absorbs K + . Distal colon also has a secretory capacity, which becomes important to K + homeostasis under pathological conditions, such as end‐stage renal failure. K + secretion in the distal colon is primarily mediated through apical large conductance (BK) channels. We hypothesized that the BK opener BMS‐204352 (BMS) and the adenylate cyclase activator forskolin (FSK) induce K + secretion through separate mechanisms. K + flux studies were performed in distal colonic mucosal tissues obtained from male Sprague‐Dawley rats (200–225g). Unidirectional 86 Rb fluxes (K + surrogate), and short‐circuit current ( I SC ) were measured under voltage‐clamped conditions in an Ussing chamber setup. Fluxes were performed in the presence of amiloride (10 mM) to inhibit ENaC‐mediated I SC , as well as VO 4 (1mM) to inhibit apical H + /K + ATPase and unmask BK‐mediated K + secretion. Results indicate that BMS (10mM) and FSK (10mM) induced a net K + secretion of 0.083 ± 0.04 and 0.274 ± 0.05 mEq/cm 2 ·hr, respectively (n=4, p<0.05). FSK, but not BMS, increased I SC compared to baseline (220.5 ± 30.5 vs 132.2 ± 18.7 uA/cm 2 ). Immunofluorescence studies performed on the same tissues used in flux experiments showed markedly increased apical BK staining in tissues exposed to FSK, but not in those exposed to only BMS. Taken together, these data suggest that while BMS may only open BK channels already present on apical membranes, FSK may cause further K + secretion by triggering the insertion of more BK channels into the apical membrane. Support or Funding Information • R01 DK104791/DK/NIDDK NIH HHS/United States