Mechanisms of TNF-alpha stimulation of amiloride-sensitive sodium transport across alveolar epithelium.
Because tumor necrosis factor (TNF)-alpha can upregulate alveolar fluid clearance (AFC) in pneumonia or septic peritonitis, the mechanisms responsible for the TNF-alpha-mediated increase in epithelial fluid transport were studied. In rats, 5 microg of TNF-alpha in the alveolar instillate increased AFC by 67%. This increase was inhibited by amiloride but not by propranolol. We also tested a triple-mutant TNF-alpha that is deficient in the lectinlike tip portion of the molecule responsible for its membrane conductance effect; the mutant also has decreased binding affinity to both TNF-alpha receptors. The triple-mutant TNF-alpha did not increase AFC. Perfusion of human A549 cells, patched in the whole cell mode, with TNF-alpha (120 ng/ml) resulted in a sustained increase in Na(+) currents from 82 +/- 9 to 549 +/- 146 pA (P < 0.005; n = 6). The TNF-alpha-elicited Na(+) current was inhibited by amiloride, and there was no change when A549 cells were perfused with the triple-mutant TNF-alpha or after preincubation with blocking antibodies to the two TNF-alpha receptors before perfusion with TNF-alpha. In conclusion, although TNF- alpha can initiate acute inflammation and edema formation in the lung, TNF-alpha can also increase AFC by an amiloride-sensitive, cAMP-independent mechanism that enhances the resolution of alveolar edema in pathological conditions by either binding to its receptors or activating Na(+) channels by means of its lectinlike domain.
Fukuda
N
N
Cardiovascular Research Institute, University of California, 505 Parnassus Ave., San Francisco, CA 94143-0130, USA.
Jayr
C
C
Lazrak
A
A
Wang
Y
Y
Lucas
R
R
Matalon
S
S
Matthay
M A
MA
D000318:Adrenergic beta-Agonists / Q000008:administration & dosage; D000319:Adrenergic beta-Antagonists / Q000008:administration & dosage; D000584:Amiloride / Q000008:administration & dosage*; D019943:Amino Acid Substitution; D000818:Animals; D019138:Antibodies, Blocking / Q000494:pharmacology; D015703:Antigens, CD / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D006801:Humans; D007322:Instillation, Drug; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009154:Mutation; D018408:Patch-Clamp Techniques; D011433:Propranolol / Q000008:administration & dosage; D011650:Pulmonary Alveoli / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018124:Receptors, Tumor Necrosis Factor / Q000037:antagonists & inhibitors / Q000378:metabolism; D047888:Receptors, Tumor Necrosis Factor, Type I; D047889:Receptors, Tumor Necrosis Factor, Type II; D020545:Respiratory Mucosa / Q000187:drug effects* / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000008:administration & dosage* / Q000235:genetics
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D019138:Antibodies, Blocking; D015703:Antigens, CD; D018124:Receptors, Tumor Necrosis Factor; D047888:Receptors, Tumor Necrosis Factor, Type I; D047889:Receptors, Tumor Necrosis Factor, Type II; D015222:Sodium Channels; D014409:Tumor Necrosis Factor-alpha; D000584:Amiloride; D012964:Sodium; D011433:Propranolol