Conductive Na+ transport in fetal lung alveolar apical membrane vesicles is regulated by fatty acids and G proteins.
We have characterised G protein and fatty acid regulation of the Na+ conductance in purified apical membrane vesicles prepared from late gestation fetal guinea-pig lung. Addition of 100 microM GTP gamma S or beta gamma-methylene-GTP, irreversible G protein activators, stimulated conductive 22Na+ uptake (ratio of experimental to control 1.35 +/- 0.02 and 1.34 +/- 0.05, respectively). Conversely, the addition of GDP beta S, an irreversible G protein inhibitor, reduced conductive 22Na+ uptake from 1.00 (control) to 0.79 +/- 0.04. A range of saturated (myristic, palmitic, stearic), monounsaturated (elaidic, oleic) and polyunsaturated (linoleic, arachidonic) fatty acids all stimulated conductive 22Na+ uptake, by between 1.18 +/- 0.05 to 1.56 +/- 0.13 over the control. Both arachidonic acid and GTP gamma S-dependent stimulation were abolished in the presence of 10 microM amiloride. The non-metabolisable analogue of arachidonic acid, eicosa-5,8,11,14-tetraynoic acid also stimulated conductive 22Na+ uptake. Furthermore, addition of indomethacin and nordihydroguairetic acid, inhibitors of cyclooxygenase and lipoxygenase pathways of arachidonate metabolism respectively, did not affect the arachidonic acid stimulation suggesting a direct effect of fatty acid upon the Na+ channel Since mepacrine (50 microM), a phospholipase A2 inhibitor, did not affect the GTP gamma S-stimulated conductive 22Na+ uptake, and inhibition of G protein turnover by GDP beta S did not attenuate the arachidonic acid response we conclude that these two regulatory pathways modulate alveolar Na+ transport directly and independently of each other.
Fyfe
G K
GK
Department of Child Health, Ninewells Hospital and Medical School, University of Dundee, UK.
Kemp
P J
PJ
Olver
R E
RE
D015117:5,8,11,14-Eicosatetraynoic Acid / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005227:Fatty Acids / Q000494:pharmacology*; D005333:Fetus / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006168:Guinea Pigs; D007213:Indomethacin / Q000494:pharmacology; D009637:Masoprocol / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000196:embryology* / Q000378:metabolism; D011796:Quinacrine / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013873:Thionucleotides / Q000494:pharmacology
D004791:Enzyme Inhibitors; D005227:Fatty Acids; D015222:Sodium Channels; D013873:Thionucleotides; D015117:5,8,11,14-Eicosatetraynoic Acid; D006153:Guanosine Diphosphate; D016718:Arachidonic Acid; C011265:guanosine 5'-(beta,gamma-methylene)triphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C023427:guanosine 5'-O-(2-thiodiphosphate); D009637:Masoprocol; D000584:Amiloride; D006160:Guanosine Triphosphate; D012964:Sodium; D019204:GTP-Binding Proteins; D011796:Quinacrine; D007213:Indomethacin