Martin Tresguerres

Metabolic Communication between Astrocytes and Neurons via Bicarbonate-Responsive Soluble Adenylyl Cyclase

Astrocytes are proposed to participate in brain energy metabolism by supplying substrates to neurons from their glycogen stores and from glycolysis. However, the molecules involved in metabolic sensing and the molecular pathways responsible for metabolic coupling between different cell types in the brain are not fully understood. Here we show that a recently cloned bicarbonate (HCO₃⁻) sensor, soluble adenylyl cyclase (sAC), is highly expressed in astrocytes and becomes activated in response to HCO₃⁻ entry via the electrogenic NaHCO₃ cotransporter (NBC). Activated sAC increases intracellular cAMP levels, causing glycogen breakdown, enhanced glycolysis, and the release of lactate into the extracellular space, which is subsequently taken up by neurons for use as an energy substrate. This process is recruited over a broad physiological range of [K⁺](ext) and also during aglycemic episodes, helping to maintain synaptic function. These data reveal a molecular pathway in astrocytes that is responsible for brain metabolic coupling to neurons.

CO2-induced ocean acidification increases anxiety in Rockfish via alteration of GABAA receptor functioning

The average surface pH of the ocean is dropping at a rapid rate due to the dissolution of anthropogenic CO2, raising concerns for marine life. Additionally, some coastal areas periodically experience upwelling of CO2-enriched water with reduced pH. Previous research has demonstrated ocean acidification (OA)-induced changes in behavioural and sensory systems including olfaction, which is due to altered function of neural gamma-aminobutyric acid type A (GABAA) receptors. Here, we used a camera-based tracking software system to examine whether OA-dependent changes in GABAA receptors affect anxiety in juvenile Californian rockfish (Sebastes diploproa). Anxiety was estimated using behavioural tests that measure light/dark preference (scototaxis) and proximity to an object. After one week in OA conditions projected for the next century in the California shore (1125 ± 100 µatm, pH 7.75), anxiety was significantly increased relative to controls (483 ± 40 µatm CO2, pH 8.1). The GABAA-receptor agonist muscimol, but not the antagonist gabazine, caused a significant increase in anxiety consistent with altered Cl− flux in OA-exposed fish. OA-exposed fish remained more anxious even after 7 days back in control seawater; however, they resumed their normal behaviour by day 12. These results show that OA could severely alter rockfish behaviour; however, this effect is reversible.

Regulation of branchial V-H+-ATPase, Na+/K+-ATPase and NHE2 in response to acid and base infusions in the Pacific spiny dogfish (Squalus acanthias)

SUMMARY To study the mechanisms of branchial acid-base regulation, Pacific spiny dogfish were infused intravenously for 24 h with either HCl (495± 79μ mol kg-1 h-1) or NaHCO3 (981±235μ mol kg-1 h-1). Infusion of HCl produced a transient reduction in blood pH. Despite continued infusion of acid, pH returned to normal by 12 h. Infusion of NaHCO3 resulted in a new steady-state acid-base status at ∼0.3 pH units higher than the controls. Immunostained serial sections of gill revealed the presence of separate vacuolar proton ATPase (V-H+-ATPase)-rich or sodium-potassium ATPase (Na+/K+-ATPase)-rich cells in all fish examined. A minority of the cells also labeled positive for both transporters. Gill cell membranes prepared from NaHCO3-infused fish showed significant increases in both V-H+-ATPase abundance (300±81%) and activity. In addition, we found that V-H+-ATPase subcellular localization was mainly cytoplasmic in control and HCl-infused fish, while NaHCO3-infused fish demonstrated a distinctly basolateral staining pattern. Western analysis in gill membranes from HCl-infused fish also revealed increased abundance of Na+/H+ exchanger 2 (213±5%) and Na+/K+-ATPase (315±88%) compared to the control.

Physiological carbon dioxide, bicarbonate, and pH sensing

In biological systems, carbon dioxide exists in equilibrium with bicarbonate and protons. The individual components of this equilibrium (i.e., CO2, HCO3−, and H+), which must be sensed to be able to maintain cellular and organismal pH, also function as signals to modulate multiple physiological functions. Yet, the molecular sensors for CO2/HCO3−/pH remained unknown until recently. Here, we review recent progress in delineating molecular and cellular mechanisms for sensing CO2, HCO3−, and pH.

Microtubule-dependent relocation of branchial V-H+-ATPase to the basolateral membrane in the Pacific spiny dogfish (Squalus acanthias): a role in base secretion.

SUMMARY We have previously shown that continuous intravenous infusion of NaHCO3 for 24 h (∼1000 μmol kg-1 h-1) results in the relocation of V-H+-ATPase from the cytoplasm to the basolateral membrane in the gills of the Pacific dogfish. To further investigate this putative base-secretive process we performed similar experiments with the addition of colchicine, an inhibitor of cytoskeleton-dependent cellular trafficking processes. Blood pH and plasma total CO2 were significantly higher in the colchicines-treated, HCO3--infused fish compared with fish infused with HCO3- alone. The effect of colchicine was highest after 24 h of infusion (8.33±0.06 vs 8.02±0.03 pH units, 15.72±3.29 vs 6.74±1.34 mmol CO2 l-1, N=5). Immunohistochemistry and western blotting confirmed that colchicine blocked the transit of V-H+-ATPase to the basolateral membrane. Furthermore, western blotting analyses from whole gill and cell membrane samples suggest that the short-term (6 h) response to alkaline stress consists of relocation of V-H+-ATPases already present in the cell to the basolateral membrane, while in the longer term (24 h) there is both relocation of preexistent enzyme and upregulation in the synthesis of new units. Our results strongly suggest that cellular relocation of V-H+-ATPase is necessary for enhanced HCO3- secretion across the gills of the Pacific dogfish.

Chloride uptake and base secretion in freshwater fish: a transepithelial ion-transport metabolon?

Despite all the efforts and technological advances during the last few decades, the cellular mechanisms for branchial chloride uptake in freshwater (FW) fish are still unclear. Although a tight 1:1 link with \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Somatic ‘Soluble’ Adenylyl Cyclase Isoforms Are Unaffected in Sacytm1Lex/Sacytm1Lex ‘Knockout’ Mice

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Coral host cells acidify symbiotic algal microenvironment to promote photosynthesis

\end{document} secretion has been established, not much is known about the identity of the ion‐transporting proteins involved or the energizing steps that allow for the inward transport of Cl− against the concentration gradient. We propose a new model for Cl− uptake in FW fish whereby the combined action of an apical anion exchanger, cytoplasmic carbonic anhydrase, and basolateral V‐type H+‐ATPase creates a local [ \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape