Key points• Rapid exchange of metabolites like glucose and lactate between different cell types is crucial for energy supply to the brain.• Carbonic anhydrase 2 (CAII) enhances lactate transport in mouse cerebellar and cerebral astrocytes.• Enhancement of transport activity is independent of the enzyme's catalytic function, but requires binding of CAII to the C-terminal tail of the monocarboxylate transporter MCT1.• CAII could enhance lactate flux by acting as a 'proton collecting antenna' for MCT1.• By this mechanism CAII could enhance transfer of lactate between astrocytes and neurons and thus provide neurons with an increased supply of energy substrate.Abstract Rapid exchange of metabolites between different cell types is crucial for energy homeostasis of the brain. Besides glucose, lactate is a major metabolite in the brain and is primarily produced in astrocytes. In the present study, we report that carbonic anhydrase 2 (CAII) enhances both influx and efflux of lactate in mouse cerebellar astrocytes. The augmentation of lactate transport is independent of the enzyme's catalytic activity, but requires direct binding of CAII to the C-terminal of the monocarboxylate transporter MCT1, one of the major lactate/proton cotransporters in astrocytes and most tissues. By employing its intramolecular proton shuttle, CAII, bound to MCT1, can act as a 'proton collecting antenna' for the transporter, suppressing the formation of proton microdomains at the transporter-pore and thereby enhancing lactate flux. By this mechanism CAII could enhance transfer of lactate between astrocytes and neurons and thus provide the neurons with an increased supply of energy substrate. Abbreviations 4-MI, 4-methylimidazole; aCSF, artificial cerebrospinal fluid; AE1, anion exchanger isoform 1; BCA, bichionic acid; CA, carbonic anhydrase; Car2, carbonic anhydrase II coding gene; CD147, cluster of differentiation 147; Co-IP, co-immunoprecipitation; EAAT, excitatory amino acid transporter; GFAP, glial fibrillary acidic protein; GST, glutathione S-transferase; gp70, glycoprotein 70; MCT, monocarboxylate transporter; m/z, mass-to-charge ratio; NBCe1, electrogenic sodium bicarbonate cotransporter isoform 1; NHE1, sodium/hydrogen exchanger isoform 1; PDB, protein data bank; PLA, proximity ligation assay.

Background: Carbonic anhydrase II (CAII) augments activity of monocarboxylate transporters (MCTs) by noncatalytic interaction. Results: CAII binds to an acidic cluster with an appropriate context in the MCT C terminus. Conclusion: Isoform-specific interaction between MCTs and CAII requires a specific binding moiety. Significance: CAII-mediated increase in lactate transport depends on the presence of a specific binding moiety in MCT.Proton-coupled monocarboxylate transporters (MCTs) mediate the exchange of high energy metabolites like lactate between different cells and tissues. We have reported previously that carbonic anhydrase II augments transport activity of MCT1 and MCT4 by a noncatalytic mechanism, while leaving transport activity of MCT2 unaltered. In the present study, we combined electrophysiological measurements in Xenopus oocytes and pulldown experiments to analyze the direct interaction between carbonic anhydrase II (CAII) and MCT1, MCT2, and MCT4, respectively. Transport activity of MCT2-WT, which lacks a putative CAII-binding site, is not augmented by CAII. However, introduction of a CAII-binding site into the C terminus of MCT2 resulted in CAII-mediated facilitation of MCT2 transport activity. Interestingly, introduction of three glutamic acid residues alone was not sufficient to establish a direct interaction between MCT2 and CAII, but the cluster had to be arranged in a fashion that allowed access to the binding moiety in CAII. We further demonstrate that functional interaction between MCT4 and CAII requires direct binding of the enzyme to the acidic cluster 431 EEE in the C terminus of MCT4 in a similar fashion as previously shown for binding of CAII to the cluster 489 EEE in the C terminus of MCT1. In CAII, binding to MCT1 and MCT4 is mediated by a histidine residue at position 64. Taken together, our results suggest that facilitation of MCT transport activity by CAII requires direct binding between histidine 64 in CAII and a cluster of glutamic acid residues in the C terminus of the transporter that has to be positioned in surroundings that allow access to CAII.

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Mosquitoes are the most important vector of arboviruses; thus, controlling mosquito population is a key point for controlling these diseases. Two major factors that influence mosquito population size are the availability of blood hosts and suitable oviposition sites. Behavioral mechanisms by which Culex pipiens biotype molestus mosquitoes locate their hosts or oviposition sites are influenced by physical and chemical factors. The present study evaluated the impact of the colors (for human eyes) red, green, blue and yellow in combination with different light intensities on preferences for oviposition and foraging sites under laboratory conditions. We identified the color red as the overall favored color for both target behaviors, which was only surpassed by black as the foraging stimulus. Altogether, we described two new inexpensive and simple bioassays, which can be used as a mosquito-tracking method for behavioral tests and as an oviposition trap to monitor Culex pipiens biotype molestus populations.

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