title: GPI-anchored carbonic anhydrase IV displays both intra- and extracellular activity in cRNA-injected oocytes and in mouse neurons.
abstract: Soluble cytosolic carbonic anhydrases (CAs) are well known to participate in pH regulation of the cytoplasm of mammalian cells. Membrane-bound CA isoforms--such as isoforms IV, IX, XII, XIV, and XV--also catalyze the reversible conversion of carbon dioxide to protons and bicarbonate, but at the extracellular face of the cell membrane. When human CA isoform IV was heterologously expressed in Xenopus oocytes, we observed, by measuring H(+) at the outer face of the cell membrane and in the cytosol with ion-selective microelectrodes, not only extracellular catalytic CA activity but also robust intracellular activity. CA IV expression in oocytes was confirmed by immunocytochemistry, and CA IV activity measured by mass spectrometry. Extra- and intracellular catalytic activity of CA IV could be pharmacologically dissected using benzolamide, the CA inhibitor, which is relatively slowly membrane-permeable. In acute cerebellar slices of mutant mice lacking CA IV, cytosolic H(+) shifts of granule cells following CO(2) removal/addition were significantly slower than in wild-type mice. Our results suggest that membrane-associated CA IV contributes robust catalytic activity intracellularly, and that this activity participates in regulating H(+) dynamics in the cytosol, both in injected oocytes and in mouse neurons.
authors.affiliation: Abteilung für Allgemeine Zoologie, Fachbereich Biologie, University of Kaiserslautern, D-67653 Kaiserslautern, Germany.
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Schneider
authors.forename: Marco D
authors.initials: MD
authors.lastname: Alt
authors.forename: Michael
authors.initials: M
authors.lastname: Klier
authors.forename: Alena
authors.initials: A
authors.lastname: Spiess
authors.forename: Fabian T
authors.initials: FT
authors.lastname: Andes
authors.forename: Abdul
authors.initials: A
authors.lastname: Waheed
authors.forename: William S
authors.initials: WS
authors.lastname: Sly
authors.forename: Holger M
authors.initials: HM
authors.lastname: Becker
authors.forename: Joachim W
authors.initials: JW
authors.lastname: Deitmer
mesh_terms: D000818:Animals; D001574:Benzolamide / Q000494:pharmacology; D024402:Carbonic Anhydrase II / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D030741:Carbonic Anhydrase IV / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D002531:Cerebellum / Q000166:cytology / Q000201:enzymology; D003600:Cytosol / Q000201:enzymology; D045604:Extracellular Fluid / Q000201:enzymology; D005260:Female; D058851:GPI-Linked Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000201:enzymology; D051379:Mice; D018345:Mice, Knockout; D009474:Neurons / Q000201:enzymology; D009865:Oocytes / Q000201:enzymology; D018075:RNA, Complementary / Q000235:genetics; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D002257:Carbonic Anhydrase Inhibitors; D058851:GPI-Linked Proteins; D018075:RNA, Complementary; D011994:Recombinant Proteins; D024402:Carbonic Anhydrase II; D030741:Carbonic Anhydrase IV; C548247:CA4 protein, human; C548248:Car4 protein, mouse; D001574:Benzolamide