Charge compensation for NADPH oxidase activity in microglia in rat brain slices does not involve a proton current.
The membrane properties of isolated cultured microglia have been extensively studied but it is important to understand their properties in situ, where they protect the brain against infection, but also contribute to neurodegenerative diseases. Microglia and macrophages attack bacteria by generating reactive oxygen species, a process which involves NADPH oxidase pumping electrons out across the cell membrane. The resulting inward current evokes a depolarization, which would inhibit the activity of the NADPH oxidase if there were no charge-compensating current which moves positive charge out across the membrane. The mechanism of this charge compensation is controversial. In neutrophils and in cultured microglia a depolarization-activated H(+) conductance has been proposed to provide charge compensation, and also to remove protons generated intracellularly by the NADPH oxidase. Alternatively, a depolarization-activated K(+) conductance has been proposed to mediate charge compensation. Here we show that in microglia, either in the resting state or when activated by the bacterial coat component lipopolysaccharide, both in acute and in cultured hippocampal slices, no significant H(+) current is detectable. This implies that the membrane properties of microglia in their normal cellular environment differ from those of cultured microglia (similarly, microglia generated a current in response to ATP but, unlike in culture, not to glutamate or GABA). Furthermore, the K(+) current (Kv1.3) that is activated by lipopolysaccharide is inactivated by depolarization, making it unsuitable for mediating charge compensation on a long time scale at positive voltages. Instead, charge compensation may be mediated by a previously undescribed non-selective cation current.
De Simoni
Anna
A
Department of Physiology, University College London, London, UK.
Allen
Nicola J
NJ
Attwell
David
D
D000818:Animals; D048430:Cell Shape; D002478:Cells, Cultured; D003022:Clotrimazole / Q000378:metabolism; D005439:Flufenamic Acid / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology; D051664:Kv1.3 Potassium Channel / Q000378:metabolism; D007811:Lanthanum / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D017628:Microglia / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D019255:NADPH Oxidases / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011522:Protons; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D050053:TRPM Cation Channels / Q000378:metabolism
D051664:Kv1.3 Potassium Channel; D008070:Lipopolysaccharides; D018377:Neurotransmitter Agents; D011522:Protons; D017382:Reactive Oxygen Species; D050053:TRPM Cation Channels; D005439:Flufenamic Acid; D007811:Lanthanum; D019255:NADPH Oxidases; D003022:Clotrimazole
Nature. 2002 Mar 21;416(6878):291-7
11907569
Prog Neurobiol. 2001 Jun;64(3):277-305
11240310
J Physiol. 2005 Sep 15;567(Pt 3):869-90
16020460
Mol Cell Neurosci. 2004 Feb;25(2):312-22
15019947
Philos Trans R Soc Lond B Biol Sci. 2005 Dec 29;360(1464):2293-300
16321799
Nat Rev Neurosci. 2007 Jan;8(1):57-69
17180163
Nature. 2004 Feb 26;427(6977):853-8
14985765
Annu Rev Immunol. 2005;23:197-223
15771570
J Neurosci. 1993 Oct;13(10):4412-21
8410196
Neuropharmacology. 2004 Sep;47(3):450-60
15275834
Nature. 2003 Apr 3;422(6931):531-4
12673252
Proc Natl Acad Sci U S A. 2004 Jul 13;101(28):10482-7
15240890
J Physiol. 2001 Sep 15;535(Pt 3):783-94
11559775
J Neurocytol. 1987 Apr;16(2):249-60
3625239
Sci STKE. 2004 May 11;2004(233):pe21
15150421
J Neurosci. 2005 Aug 3;25(31):7139-49
16079396
Pflugers Arch. 1995 Aug;430(4):526-33
7491279
Glia. 1996 Jul;17(3):225-36
8840164
J Gen Physiol. 1988 Jan;91(1):49-72
3125305
Biochem J. 1994 Jan 1;297 ( Pt 1):217-23
8280102
Eur J Neurosci. 2003 Jun;17(11):2267-76
12814360
J Neurochem. 2007 Jan;100(2):503-19
17241161
Am J Physiol Cell Physiol. 2001 Apr;280(4):C796-806
11245596
Glia. 1996 Dec;18(4):319-31
8972800
Biophys J. 1991 Nov;60(5):1243-53
1722118
Am J Physiol Cell Physiol. 2004 Jan;286(1):C129-37
14512294
J Neurosci Res. 1995 Nov 1;42(4):439-51
8568930
Neuroscience. 1997 Jun;78(4):1217-28
9174088
Philos Trans R Soc Lond B Biol Sci. 2005 Dec 29;360(1464):2315-25
16321802
J Neurosci Methods. 1991 Apr;37(2):173-82
1715499
Nat Protoc. 2006;1(3):1439-45
17406432
Eur J Neurosci. 2000 Jun;12(6):2049-58
10886344
J Neurosci Res. 1992 Oct;33(2):218-30
1333539
J Immunol. 2003 Feb 1;170(3):1167-73
12538672
Hippocampus. 1998;8(5):458-74
9825958
Eur J Neurosci. 2003 Nov;18(10):2893-8
14656339
J Neurosci. 1998 Sep 15;18(18):7127-37
9736636
Mol Cell Neurosci. 2005 May;29(1):128-38
15866053
J Physiol. 2003 Jul 15;550(Pt 2):447-58
12754316
Neurosci Lett. 1992 Dec 7;147(2):171-4
1491802
Glia. 2001 Mar 1;33(3):256-66
11241743
J Neurosci. 2000 Jan 1;20(1):251-8
10627602
J Gen Physiol. 2006 Jun;127(6):659-72
16702353
Neuropharmacology. 2006 Jan;50(1):89-97
16260005
J Physiol. 2002 Nov 15;545(1):93-105
12433952
Biophys J. 1993 Oct;65(4):1590-8
7506066
Trends Pharmacol Sci. 2004 Dec;25(12):633-9
15530641
Neuroscience. 1999;92(4):1465-74
10426500
Mol Pharmacol. 1994 Jun;45(6):1227-34
7517498
J Neurosci Res. 1996 Nov 01;46(3):294-304
8933368
Neuroscience. 2005;135(4):1155-66
16165295