Journal: Nature Neuroscience
Article Title: Oligodendrocyte–axon metabolic coupling is mediated by extracellular K + and maintains axonal health
doi: 10.1038/s41593-023-01558-3
Figure Lengend Snippet: a , OL Ca 2+ levels increased by increasing [K + ] ext with 5, 10 and 30 mM K + (30-s bath application: Δ[K + ] bath ). Left, average OL Ca 2+ traces (mean ± s.e.m.). Right, quantification of Δ[K + ] bath -evoked signal amplitudes (30 mM: n = 57 cells from four mice; 10 mM: n = 52 cells from five mice; 5 mM: n = 35 cells from four mice; 5 versus 10 mM, ** P = 0.0048; 5 versus 30 mM, *** P < 0.0001; 10 versus 30 mM, *** P < 0.0001; one-way ANOVA with Tukey’s multiple-comparison test). b , Left, K + -evoked OL Ca 2+ response independent of axonal spiking activity, showing comparable surges with TTX. Right, box plots showing the normalized response AUCs ( n = 72 cells from five mice; P = 0.8144, two-sided paired t test; NS, not significant). c , Left, barium (Ba 2+ , 100 µM) reversibly inhibited the 50-Hz-induced OL Ca 2+ surge by 84 ± 10%. Right, box plots showing the normalized response AUCs ( n = 45 cells from four mice; *** P < 0.0001, two-sided paired t test). d , Left, Ba 2+ reduced the K + -evoked OL Ca 2+ response by 88 ± 9%. Right, box plots showing the normalized response AUCs ( n = 47 cells from three mice; *** P < 0.0001, two-sided paired t test). e , f , Reverse-mode NCX blocker KB-R7943 (25 μM) reduced the 50-Hz-induced Ca 2+ increase ( e ) by 44 ± 11% ( n = 64 cells from five mice; paired t test, *** P = 0.0002) and the K + -evoked Ca 2+ response ( f ) by 47 ± 8% ( n = 52 cells from three mice; two-sided paired t test, *** P < 0.0001). Box plots on the right show the normalized response AUCs. g , Summary of drugs tested and their inhibitory effects on 50-Hz-evoked OL Ca 2+ surges (data are also shown as box plots including the respective P values in c and e , Fig. , and Extended Data Figs. , and ): TTX ( n = 82), zero Ca 2+ ( n = 44), BaCl ( n = 45), KB-R7943 ( n = 64), SEA0400 ( n = 54), CdCl ( n = 54), NiCl ( n = 60), nifedipine ( n = 39), benidipine ( n = 56), RuR ( n = 71), bumetanide ( n = 77), PPADS ( n = 46), suramin ( n = 33), NBQX ( n = 45) and +DAP-5/7-CKA ( n = 33). AMPAR, AMPA receptor; NMDAR, NMDA receptor. h , Schematic of axonal activity-mediated OL Ca 2+ activation: high-frequency axonal activity increases [K + ] ext , depolarizing (Depol.) OLs through Kir4.1 and enhancing Ca 2+ entry through NCX. Minor contributions of VGCCs, P2XR and NMDA receptors are illustrated. Box plots in a – f show the median (center line), quartiles (box bounds), mean (+) and 5th–95th percentiles (whiskers).
Article Snippet: Stock solutions (1,000×) of the following drugs were prepared: TTX (ab120054, Abcam), D-AP5 (0106, Tocris), PPADS (ab120009, Abcam), suramin (1472, Tocris), ouabain (O3125, Sigma-Aldrich), RuR (1439, Tocris), BaCl 2 (342920, Sigma-Aldrich), CdCl 2 (202908, Sigma-Aldrich), NiCl 2 (339350, Sigma-Aldrich), IA (I2512, Sigma-Aldrich), NaN 3 (S2002, Sigma-Aldrich), NBQX (ab120045, Abcam), 7-CKA (ab120024, Abcam), nifedipine (1075, Tocris), benidipine (3934, Tocris), bumetanide (3108, Tocris), SEA0400 (6164, Tocris), KB-R7943 (ab120284, Abcam) and CytoB (5474, Tocris).
Techniques: Comparison, Activity Assay, Activation Assay
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![a , OL Ca 2+ levels increased by increasing [K + ] ext with 5, 10 and 30 mM K + (30-s bath application: Δ[K + ] bath ). Left, average OL Ca 2+ traces (mean ± s.e.m.). Right, quantification of Δ[K + ] bath -evoked signal amplitudes (30 mM: n = 57 cells from four mice; 10 mM: n = 52 cells from five mice; 5 mM: n = 35 cells from four mice; 5 versus 10 mM, ** P = 0.0048; 5 versus 30 mM, *** P < 0.0001; 10 versus 30 mM, *** P < 0.0001; one-way ANOVA with Tukey’s multiple-comparison test). b , Left, K + -evoked OL Ca 2+ response independent of axonal spiking activity, showing comparable surges with TTX. Right, box plots showing the normalized response AUCs ( n = 72 cells from five mice; P = 0.8144, two-sided paired t test; NS, not significant). c , Left, barium (Ba 2+ , 100 µM) reversibly inhibited the 50-Hz-induced OL Ca 2+ surge by 84 ± 10%. Right, box plots showing the normalized response AUCs ( n = 45 cells from four mice; *** P < 0.0001, two-sided paired t test). d , Left, Ba 2+ reduced the K + -evoked OL Ca 2+ response by 88 ± 9%. Right, box plots showing the normalized response AUCs ( n = 47 cells from three mice; *** P < 0.0001, two-sided paired t test). e , f , Reverse-mode NCX blocker KB-R7943 (25 μM) reduced the 50-Hz-induced Ca 2+ increase ( e ) by 44 ± 11% ( n = 64 cells from five mice; paired t test, *** P = 0.0002) and the K + -evoked Ca 2+ response ( f ) by 47 ± 8% ( n = 52 cells from three mice; two-sided paired t test, *** P < 0.0001). Box plots on the right show the normalized response AUCs. g , Summary of drugs tested and their inhibitory effects on 50-Hz-evoked OL Ca 2+ surges (data are also shown as box plots including the respective P values in c and e , Fig. , and Extended Data Figs. , and ): TTX ( n = 82), zero Ca 2+ ( n = 44), BaCl ( n = 45), KB-R7943 ( n = 64), SEA0400 ( n = 54), CdCl ( n = 54), NiCl ( n = 60), nifedipine ( n = 39), benidipine ( n = 56), RuR ( n = 71), bumetanide ( n = 77), PPADS ( n = 46), suramin ( n = 33), NBQX ( n = 45) and +DAP-5/7-CKA ( n = 33). AMPAR, AMPA receptor; NMDAR, NMDA receptor. h , Schematic of axonal activity-mediated OL Ca 2+ activation: high-frequency axonal activity increases [K + ] ext , depolarizing (Depol.) OLs through Kir4.1 and enhancing Ca 2+ entry through NCX. Minor contributions of VGCCs, P2XR and NMDA receptors are illustrated. Box plots in a – f show the median (center line), quartiles (box bounds), mean (+) and 5th–95th percentiles (whiskers).](https://pub-med-central-images-cdn.bioz.com/pub_med_central_ids_ending_with_7689/pmc10917689/pmc10917689__41593_2023_1558_Fig2_HTML.jpg)