Ammonia blockade of intestinal epithelial K+ conductance.
Ammonia profoundly inhibits cAMP-dependent Cl- secretion in model T84 human intestinal crypt epithelia. Because colonic lumen concentrations of ammonia are high (10-70 mM), ammonia may be a novel regulator of secretory diarrheal responsiveness. We defined the target of ammonia action by structure-function analysis with a series of primary amines (ammonia, methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, and octylamine) that vary principally in size and lipid solubilities. The amine concentrations required for 50% inhibition of Cl- secretion in intact monolayers and 50% inhibition of outward K+ current (IK) in apically permeabilized monolayers vs. the logs of the respective amine partition coefficients give two plots that are strikingly similar in character. Half-maximal inhibition of short-circuit current (Isc) by ammonia was seen at 6 mM and for IK at 4 mM; half-maximal inhibition for octylamine was 0.24 mM and 0.19 mM for Isc and IK, respectively. The preferentially water-soluble hydrophilic amines (ammonia, methylamine, ethylamine) increase in blocking ability with decreasing size and lipophilicity. Conversely, the preferentially lipid-soluble hydrophobic (propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine) amines increase in blocking ability with increasing size and lipophilicity. Ammonia does not affect isolated apical Cl- conductance; amine-induced changes in cytosolic and endosomal pH do not correlate with secretory inhibition. We propose that ammonia in its protonated ammonium form (NH4+) inhibits cAMP-dependent Cl- secretion in T84 monolayers by blocking basolateral K+ channels.
Hrnjez
B J
BJ
Department of Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, and the Harvard Digestive Diseases Center, Boston, Massachusetts 02215, USA.
Song
J C
JC
Prasad
M
M
Mayol
J M
JM
Matthews
J B
JB
D000588:Amines / Q000737:chemistry / Q000494:pharmacology; D000641:Ammonia / Q000494:pharmacology*; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D002712:Chlorides / Q000037:antagonists & inhibitors / Q000502:physiology; D000242:Cyclic AMP / Q000502:physiology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology*; D011188:Potassium / Q000037:antagonists & inhibitors / Q000502:physiology*
D000588:Amines; D002712:Chlorides; D000641:Ammonia; D000242:Cyclic AMP; D011188:Potassium