title: Modification of ion transport in lipid bilayer membranes in the presence of 2,4-dichlorophenoxyacetic acid. I. Enhancement of cationic conductance and changes of the kinetics of nonactin-mediated transport of potassium.
abstract: We have found that herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) has the ability to increase the rate of transport of positive ions of several kinds, and to inhibit transport of negatively charged tetraphenylborate ions in lipid bilayer membranes. It has been found that only the neutral form of 2,4-D is transport active, whereas the ionized from of 2,4-D does not modify transport of ions, and does not by itself permeate through lipid membranes. The results suggest that the enhancement of transport of positively charged ions such as tetraphenylarsonium + and nonactin-K+ is dominated by the increase of the ion translocation rate constant. It has been shown that the enhancement of nonactin-mediated transport of K+ by 2,4-D can be accounted for by a simple carrier model. We have observed that a 2,4-D concentration above 3 X 10(-4) M the potassium ion transport in phosphatidylcholine-cholesterol as well as in cholesterol-free glycerolmonooleate membranes is enhanced to such a degree that, depending upon the concentration of potassium ions, it becomes limited by the rate of recombination of K+ with nonactin, and/or by backdiffusion of unloaded nonactin molecules. Furthermore, the effect of 2,4-D is enhanced by ionic strength of aqueous solution. From the changes of kinetic parameters of nonactin-K+ transport, as well as from the changes of membranes conductance due to tetraphenylarsonium + ions, we have estimated the changes of the electrical potential of the membrane interior. We have found that the potential of the interior of the membrane becomes more negative in the presence of 2,4-D, and that its change is proportional to the aqueous concentration of 2,4-D. The effect of 2,4-D on ion transport has been attributed to a layer of 2,4-D molecules absorbed within the interfacial region, and having a dipole moment directed toward the aqueous medium. The results of kinetic studied of nonactin-K+ transport suggest that this layer is located on the hydrocarbon side of the interface.
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid; D000900:Anti-Bacterial Agents; D001692:Biological Transport; D004553:Electric Conductivity; D007700:Kinetics; D008051:Lipid Bilayers; D018942:Macrolides; D008433:Mathematics; D008954:Models, Biological; D011188:Potassium
chemical_list: D000900:Anti-Bacterial Agents; D008051:Lipid Bilayers; D018942:Macrolides; D015084:2,4-Dichlorophenoxyacetic Acid; D011188:Potassium; C050476:nonactin
references.citation: Nature. 1978 Mar 16;272(5650):268-70
references.pmid: 628453
references.citation: Membranes. 1975;3:215-53
references.pmid: 586
references.citation: J Membr Biol. 1975 Dec 4;25(1-2):23-45
references.pmid: 2783
references.citation: J Membr Biol. 1977 Dec 15;37(3-4):361-96
references.pmid: 23435
references.citation: Biochim Biophys Acta. 1975 Jun 25;394(2):304-13
references.pmid: 166694
references.citation: Ann N Y Acad Sci. 1975 Dec 30;264:2-16
references.pmid: 769640
references.citation: Biochim Biophys Acta. 1977 Feb 4;464(3):465-81
references.pmid: 836821
references.citation: Biochim Biophys Acta. 1977 Mar 17;465(3):429-42
references.pmid: 836835
references.citation: J Agric Food Chem. 1977 Jul-Aug;25(4):898-900
references.pmid: 881513
references.citation: Biochim Biophys Acta. 1977 Jul 14;468(2):245-58
references.pmid: 884088
references.citation: FEBS Lett. 1977 Oct 15;82(2):219-22
references.pmid: 913593
references.citation: J Agric Food Chem. 1977 Nov-Dec;25(6):1308-14
references.pmid: 915130
references.citation: J Membr Biol. 1976 May;26(4):385-403
references.pmid: 933152
references.citation: J Gen Physiol. 1976 Jun;67(6):749-71
references.pmid: 946975
references.citation: Biochim Biophys Acta. 1976 Dec 14;455(3):701-20
references.pmid: 999935
references.citation: J Membr Biol. 1976 Dec 25;30(1):1-44
references.pmid: 1037004
references.citation: Membranes. 1975;3:127-214
references.pmid: 1105058
references.citation: Biophys J. 1975 Aug;15(8):795-830
references.pmid: 1148364
references.citation: J Agric Food Chem. 1975 May-Jun;23(3):373-6
references.pmid: 1150979
references.citation: J Membr Biol. 1975;22(2):125-41
references.pmid: 1170333
references.citation: Biochim Biophys Acta. 1975 Feb 14;375(3):327-49
references.pmid: 1173048
references.citation: Biochim Biophys Acta. 1975 Feb 14;375(3):350-62
references.pmid: 1173049
references.citation: Biochim Biophys Acta. 1975 Nov 17;413(1):33-44
references.pmid: 1191689
references.citation: Biophys J. 1976 Feb;16(2 Pt 1):143-50
references.pmid: 1247644
references.citation: Biophys J. 1976 Apr;16(4):319-36
references.pmid: 1252584
references.citation: J Membr Biol. 1972;10(1):67-91
references.pmid: 4120636
references.citation: Electroencephalogr Clin Neurophysiol. 1966 Dec;21(6):521-37
references.pmid: 4162882
references.citation: J Membr Biol. 1974;17(2):155-80
references.pmid: 4407660
references.citation: J Membr Biol. 1974;18(3-4):243-61
references.pmid: 4472506
references.citation: J Membr Biol. 1972;9(4):361-72
references.pmid: 4640973
references.citation: Biochim Biophys Acta. 1973 May 25;307(3):429-43
references.pmid: 4718803
references.citation: J Agric Food Chem. 1973 Jul-Aug;21(4):637-40
references.pmid: 4736996
references.citation: Biochim Biophys Acta. 1973 Oct 25;323(3):343-50
references.pmid: 4757314
references.citation: J Agric Food Chem. 1974 Mar-Apr;22(2):307-9
references.pmid: 4857862
references.citation: Biochim Biophys Acta. 1974 May 30;352(1):71-85
references.pmid: 4859535
references.citation: Biochim Biophys Acta. 1969;193(2):350-60
references.pmid: 5351950
references.citation: Biofizika. 1969 May-Jun;14(3):452-61
references.pmid: 5397714
references.citation: Biochim Biophys Acta. 1970 Apr 7;205(1):1-6
references.pmid: 5439517
references.citation: JAMA. 1970 Nov 9;214(6):1114-7
references.pmid: 5536254
references.citation: J Theor Biol. 1965 Nov;9(3):433-43
references.pmid: 5875186
references.citation: Plant Physiol. 1972 Jul;50(1):80-6
references.pmid: 16658138
references.citation: J Gen Physiol. 1977 Feb;69(2):243-57
references.pmid: 576427
references.citation: Biochim Biophys Acta. 1978 Jan 19;506(2):265-80
references.pmid: 620033
references.citation: Biophys J. 1978 Jan;21(1):35-70
references.pmid: 620077
references.citation: Biophys J. 1978 Jan;21(1):71-86
references.pmid: 620078
references.citation: J Membr Biol. 1978 Jan 12;38(1-2):1-9
references.pmid: 625048