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Localization of cAMP‐ and aldosterone‐induced K + secretion in rat distal colon by conductance scanning
Author(s) -
Grotjohann I.,
Gitter A. H.,
Köckerling A.,
Bertog M.,
Schulzke J. D.,
Fromm M.
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.561bt.x
Subject(s) - aldosterone , amiloride , chemistry , secretion , endocrinology , medicine , ouabain , ussing chamber , conductance , incubation , apical membrane , biophysics , sodium , biology , biochemistry , membrane , mathematics , organic chemistry , combinatorics
1 Aldosterone‐ and adrenaline‐induced K + secretion were investigated in rat late distal colon using conductance scanning and Ussing chamber techniques. K + secretion was unmasked by the K + channel blocker tetraethylammonium (TEA). Electrogenic Na + absorption was inhibited by amiloride. Rb + net fluxes consistently measured about 80 % of K + secretion estimated using change in short‐circuit current (Δ I SC ) measurements. 2 Partial block of K + absorption by mucosal ouabain did not change TEA‐sensitive K + secretion. Thus, K + absorption and K + secretion are not coupled. 3 Additivity of Rb + fluxes as well as Δ I SC caused by 3 nM aldosterone (6 h in vitro incubation) and, subsequently, adrenaline suggested additivity of aldosterone‐induced and cAMP‐mediated K + secretion in the presence of amiloride. 4 Conductance scanning under control conditions revealed a small TEA‐sensitive K + conductivity in surface epithelium (0.3 ± 0.2 mS cm −2 ) but not in crypts, as well as a small basal K + secretion in surface epithelium (Δ I SC = 0.3 μ m ol h −1 cm −2 ), which increased during sham incubation. 5 Aldosterone (3 nM, 6 h in vitro incubation) resulted, after correction for the basal K + secretion, in a K + secretion of Δ I SC = 0.9 μ m ol h −1 cm −2 . Aldosterone induced a TEA‐sensitive conductivity of 1.1 ± 0.3 mS cm −2 in surface epithelium, but not in crypts. 6 Adrenaline (5 μ m ) caused, in fresh tissue, a K + secretion of Δ I SC = 1.2 μ m ol h −1 cm −2 and equal conductivity changes in crypts (0.7 ± 0.2 mS cm −2 ) and surface epithelium (0.7 ± 0.1 mS cm −2 ). 7 We conclude that K + secretion induced by aldosterone in physiological concentration is restricted to surface epithelium, whereas cAMP‐mediated K + secretion is located equally in crypts and surface epithelium.