title: O2-filled swimbladder employs monocarboxylate transporters for the generation of O2 by lactate-induced root effect hemoglobin.
abstract: The swimbladder volume is regulated by O(2) transfer between the luminal space and the blood In the swimbladder, lactic acid generation by anaerobic glycolysis in the gas gland epithelial cells and its recycling through the rete mirabile bundles of countercurrent capillaries are essential for local blood acidification and oxygen liberation from hemoglobin by the "Root effect." While O(2) generation is critical for fish flotation, the molecular mechanism of the secretion and recycling of lactic acid in this critical process is not clear. To clarify molecules that are involved in the blood acidification and visualize the route of lactic acid movement, we analyzed the expression of 17 members of the H(+)/monocarboxylate transporter (MCT) family in the fugu genome and found that only MCT1b and MCT4b are highly expressed in the fugu swimbladder. Electrophysiological analyses demonstrated that MCT1b is a high-affinity lactate transporter whereas MCT4b is a low-affinity/high-conductance lactate transporter. Immunohistochemistry demonstrated that (i) MCT4b expresses in gas gland cells together with the glycolytic enzyme GAPDH at high level and mediate lactic acid secretion by gas gland cells, and (ii) MCT1b expresses in arterial, but not venous, capillary endothelial cells in rete mirabile and mediates recycling of lactic acid in the rete mirabile by solute-specific transcellular transport. These results clarified the mechanism of the blood acidification in the swimbladder by spatially organized two lactic acid transporters MCT4b and MCT1b.
authors.affiliation: Department of Biological Sciences, Tokyo Institute of Technology, Yokohama, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Umezawa
authors.forename: Akira
authors.initials: A
authors.lastname: Kato
authors.forename: Maho
authors.initials: M
authors.lastname: Ogoshi
authors.forename: Kayoko
authors.initials: K
authors.lastname: Ookata
authors.forename: Keijiro
authors.initials: K
authors.lastname: Munakata
authors.forename: Yoko
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Zinia
authors.initials: Z
authors.lastname: Islam
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Doi
authors.forename: Michael F
authors.initials: MF
authors.lastname: Romero
authors.forename: Shigehisa
authors.initials: S
authors.lastname: Hirose
mesh_terms: D000400:Air Sacs / Q000098:blood supply / Q000502:physiology*; D000818:Animals; D024581:Glyceraldehyde-3-Phosphate Dehydrogenase (Phosphorylating); D006454:Hemoglobins / Q000378:metabolism*; D007150:Immunohistochemistry; D019344:Lactic Acid / Q000378:metabolism*; D027501:Monocarboxylic Acid Transporters / Q000235:genetics / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D023741:Takifugu / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D006454:Hemoglobins; D027501:Monocarboxylic Acid Transporters; D019344:Lactic Acid; D024581:Glyceraldehyde-3-Phosphate Dehydrogenase (Phosphorylating); D010100:Oxygen