Effects of ammonium on ion channels and transporters in colonic secretory cells.
Basolateral ammonium produces an inhibition of Cl- secretion the magnitude of which is dependent on the NH4+ to K+ concentration ratio. Inhibition is maximal at a mole fraction ratio of 0.25 K+ to NH4+. This anomalous mole fraction effect is due to effects on the basolateral K+ channel as well as Na(+)-K(+)-2Cl- cotransporter. However, only Cl- loading, not K+ loading, appears affected in an anomalous mole fraction manner. Transepithelial current is only slightly inhibited relative to equilmolar K+ by NH4+. As in other systems, both Na(+)-K(+)-ATPase and Na(+)-K(+)-2Cl- can act in Na(+)-NH4(+)-ATPase and Na(+)-NH4(+)-2Cl- transport modes. NH4+ conducts through most K+ channels and thus likely through the apical K+ channel present in native crypt cells. This suggests that, similar to the kidney, colonic secretory cells have the capacity to secrete NH4+ when in a K(+)-secreting mode with elevated basolateral NH4+ levels.
Worrell
Roger T
RT
Department of Surgery, University of Cincinnati, Cincinnati, OH 45219, USA. roger.worrell@uc.edu
Matthews
Jeffrey B
JB
D000818:Animals; D003106:Colon / Q000166:cytology* / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D007473:Ion Channels; D026901:Membrane Transport Proteins; D000644:Quaternary Ammonium Compounds; D000254:Sodium-Potassium-Exchanging ATPase