title: Arachidonic acid-induced H+ and Ca2+ increases in both the cytoplasm and nucleoplasm of rat cerebellar granule cells.
abstract: 1. Arachidonic acid (AA) exerts multiple physiological and pathophysiological effects in the brain. By continuously measuring the intracellular pH (pH(i)) and Ca2+ levels ([Ca2+]i) in primary cultured rat cerebellar granule cells, we have found, for the first time, that 20 min treatment with 10 microM AA resulted in marked increases in Ca2+ and H+ levels in both the cytosol and nucleus. 2. A much higher concentration (40 mM) of another weak acid, propionic acid, was needed to induce a similar change in pH(i). The [Ca2+]i increase was probably caused by AA-induced activation of Ni2+-sensitive cationic channels, but did not involve NMDA channels or the Na+-Ca2+ exchanger. 3. AA-induced acidosis occurs by a different mechanism involving predominantly the passive diffusion of the un-ionized form of AA, rather than a protein carrier, as proposed by Kamp & Hamilton for fatty acids (FAs) in artificial phospholipid bilayers (the 'flip-flop' model). The following results, which are similar to those observed in lipid bilayers, support this conclusion: (1) FAs containing a -COOH group (AA, linoleic acid, alpha-linolenic acid, and docosahexaenoic acid) induced intracellular acidosis, whereas a FA with a -COOCH3 group (AA methyl ester) had little effect on pH(i), (2) a FA amine, tetradecylamine, induced intracellular alkalosis, and (3) the AA-/FA-induced pH(i) changes were reversed by bovine serum albumin. 4. Further evidence in support of a passive diffusion model, rather than a membrane protein carrier, is that: (1) there was a linear relationship between the initial rate of acid flux and the concentration of AA (2-100 microM), (2) acidosis was not inhibited by 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid, a potent inhibitor of the plasma membrane FA carrier protein, and (3) the involvement of most known H+-related membrane carriers and H+ conductance has been ruled out. 5. Since AA can be released under both physiological and pathophysiological conditions, the possible significance of the AA-evoked increases in H+ and Ca2+ in both the cytoplasm and nucleoplasm is discussed.
authors.affiliation: Institute of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: W H
authors.initials: WH
authors.lastname: Chen
authors.forename: C R
authors.initials: CR
authors.lastname: Chen
authors.forename: K T
authors.initials: KT
authors.lastname: Yang
authors.forename: W L
authors.initials: WL
authors.lastname: Chang
authors.forename: M J
authors.initials: MJ
authors.lastname: Su
authors.forename: C C
authors.initials: CC
authors.lastname: Wu
authors.forename: M L
authors.initials: ML
authors.lastname: Wu
mesh_terms: D000138:Acidosis / Q000139:chemically induced / Q000378:metabolism; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D004553:Electric Conductivity; D005227:Fatty Acids / Q000494:pharmacology; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006859:Hydrogen / Q000378:metabolism* / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D051381:Rats; D017208:Rats, Wistar; D012710:Serum Albumin, Bovine / Q000494:pharmacology
chemical_list: D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D012710:Serum Albumin, Bovine; D016718:Arachidonic Acid; D006859:Hydrogen; D002118:Calcium