| Autor: |
Grotjohann, I., Gitter, A. H., Köckerling, A., Bertog, M., Schulzke, J. D., Fromm, M. |
| Zdroj: |
Journal of Physiology; March 1998, Vol. 507 Issue: 2 p561-570, 10p |
| Abstrakt: |
1Aldosterone‐ 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 (ΔISC) measurements.2Partial block of K+absorption by mucosal ouabain did not change TEA‐sensitive K+secretion. Thus, K+absorption and K+secretion are not coupled.3Additivity of Rb+fluxes as well as ΔISCcaused by 3 nM aldosterone (6 h in vitroincubation) and, subsequently, adrenaline suggested additivity of aldosterone‐induced and cAMP‐mediated K+secretion in the presence of amiloride.4Conductance 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 (ΔISC= 0.3 μmol h−1cm−2), which increased during sham incubation.5Aldosterone (3 nM, 6 h in vitroincubation) resulted, after correction for the basal K+secretion, in a K+secretion of ΔISC= 0.9 μmol h−1cm−2. Aldosterone induced a TEA‐sensitive conductivity of 1.1 ± 0.3 mS cm−2in surface epithelium, but not in crypts.6Adrenaline (5 μm) caused, in fresh tissue, a K+secretion of ΔISC= 1.2 μmol h−1cm−2and equal conductivity changes in crypts (0.7 ± 0.2 mS cm−2) and surface epithelium (0.7 ± 0.1 mS cm−2).7We 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. |
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