Quinidine-sensitive K+ channels in the basolateral membrane of embryonic coprodeum epithelium: regulation by aldosterone and thyroxine |
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Authors: | B Illek H Fischer W Clauss |
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Institution: | (1) Institut für Tierphysiologie, Justus-Liebig-Universität, Wartweg 95, D-35392 Giessen, Germany |
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Abstract: | Basolateral K+ channels and their regulation during aldosterone- and thyroxine-stimulated Na+ transport were studied in the lower intestinal epithelium (coprodeum) of embryonic chicken in vitro. Isolated tissues of the coprodeum were mounted in Ussing chambers and investigated under voltage-clamped conditions. Simultaneous stimulation with aldosterone (1 mol·l-1) and thyroxine (1 mol·l-1) raised short-circuit current after a 1- to 2-h latent period. Maximal values were reached after 6–7 h of hormonal treatment, at which time transepithelial Na+ absorption was more than tripled (77±11 A·cm-2) compared to control (24±8 A·cm-2). K+ currents across the basolateral membrane with the pore-forming antibiotic amphotericin B and application of a mucosal-to-serosal K+ gradient. This K+ current could be dose dependently depressed by the K+ channel blocker quinidine. Fluctuation analysis of the short-circuit current revealed a spontaneous and a blocker-induced Lorentzian noise component in the power density spectra. The Lorentzian corner frequencies increased linearly with the applied blocker concentration. This enabled the calculation of single K+ channel current and K+ channel density. Single K+ channel current was not affected by stimulation, whereas the number of quinidine-sensitive K+ channels in the basolateral membrane increased from 11 to 26·106·cm-2 in parallel to the hormonal stimulation transepithelial Na+ transport. This suggests that the basolateral membrane is a physiological target during synergistic aldosterone and thyroxine regulation of transepithelial Na+ transport for maintaining intracellular K+ homeostasis.Abbreviations
f
frequency
-
f
c
Lorentzian corner frequency
-
g
K
single K+ channel conductance
- HEPES
N-2-hydroxyethylpiperazin-N'-2-ethansulfonic acid
-
i
K
single K+ channel current
- IAmpho
amphotericin B induced K+ current
-
I
sc
short-circuit current
-
I
K
quinidine blockable K+ current
-
I
max
maximally blocked current by quinidine
-
IC
50
half-maximal blocker concentration
-
k
on, k
off
on- and off-rate coefficients of reversible single channel block by quinidine
-
M
K
number of conducting K+ channels
- Q]
quinidine concentration
-
R
t
transepithelial resistance
-
S
spectral density
-
S
o
Lorentzian plateau
- TBM cells
toad urinary bladder cell line
Present address: University of California at Berkeley, Dept. of Molecular and Cell Biology Berkeley, CA 94720, USA |
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Keywords: | Epithelial transport Coprodeum Noise analysis Quinidine Chicken embryo |
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