NH4(+) triggers the release of astrocytic lactate via mitochondrial pyruvate shunting.
Neural activity is accompanied by a transient mismatch between local glucose and oxygen metabolism, a phenomenon of physiological and pathophysiological importance termed aerobic glycolysis. Previous studies have proposed glutamate and K(+) as the neuronal signals that trigger aerobic glycolysis in astrocytes. Here we used a panel of genetically encoded FRET sensors in vitro and in vivo to investigate the participation of NH4(+), a by-product of catabolism that is also released by active neurons. Astrocytes in mixed cortical cultures responded to physiological levels of NH4(+) with an acute rise in cytosolic lactate followed by lactate release into the extracellular space, as detected by a lactate-sniffer. An acute increase in astrocytic lactate was also observed in acute hippocampal slices exposed to NH4(+) and in the somatosensory cortex of anesthetized mice in response to i.v. NH4(+). Unexpectedly, NH4(+) had no effect on astrocytic glucose consumption. Parallel measurements showed simultaneous cytosolic pyruvate accumulation and NADH depletion, suggesting the involvement of mitochondria. An inhibitor-stop technique confirmed a strong inhibition of mitochondrial pyruvate uptake that can be explained by mitochondrial matrix acidification. These results show that physiological NH4(+) diverts the flux of pyruvate from mitochondria to lactate production and release. Considering that NH4(+) is produced stoichiometrically with glutamate during excitatory neurotransmission, we propose that NH4(+) behaves as an intercellular signal and that pyruvate shunting contributes to aerobic lactate production by astrocytes.
Biological Laboratory, Centro de Estudios Científicos, 5110466 Valdivia, Chile; Universidad Austral de Chile, 5110566 Valdivia, Chile;
Rodrigo
R
Lerchundi
Biological Laboratory, Centro de Estudios Científicos, 5110466 Valdivia, Chile; Universidad Austral de Chile, 5110566 Valdivia, Chile;
Ignacio
I
Fernández-Moncada
Biological Laboratory, Centro de Estudios Científicos, 5110466 Valdivia, Chile; Universidad Austral de Chile, 5110566 Valdivia, Chile;
Yasna
Y
Contreras-Baeza
Biological Laboratory, Centro de Estudios Científicos, 5110466 Valdivia, Chile; Universidad Austral de Chile, 5110566 Valdivia, Chile;
Tamara
T
Sotelo-Hitschfeld
Institute of Pharmacology and Toxicology, University of Zurich, 8057 Zurich, Switzerland; Neuroscience Center Zurich, Eidgenössische Technische Hochschule (ETH), and University of Zurich, 8057 Zurich, Switzerland.
Philipp
P
Mächler
Institute of Pharmacology and Toxicology, University of Zurich, 8057 Zurich, Switzerland; Neuroscience Center Zurich, Eidgenössische Technische Hochschule (ETH), and University of Zurich, 8057 Zurich, Switzerland.
Matthias T
MT
Wyss
Institute of Pharmacology and Toxicology, University of Zurich, 8057 Zurich, Switzerland; Neuroscience Center Zurich, Eidgenössische Technische Hochschule (ETH), and University of Zurich, 8057 Zurich, Switzerland.
Jillian
J
Stobart
Biological Laboratory, Centro de Estudios Científicos, 5110466 Valdivia, Chile;
Felipe
F
Baeza-Lehnert
Biological Laboratory, Centro de Estudios Científicos, 5110466 Valdivia, Chile;
Karin
K
Alegría
Institute of Pharmacology and Toxicology, University of Zurich, 8057 Zurich, Switzerland; Neuroscience Center Zurich, Eidgenössische Technische Hochschule (ETH), and University of Zurich, 8057 Zurich, Switzerland.
Bruno
B
Weber
Biological Laboratory, Centro de Estudios Científicos, 5110466 Valdivia, Chile; fbarros@cecs.cl.
L Felipe
LF
Barros
D064751:Ammonium Compounds / Q000378:metabolism*; D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D019344:Lactic Acid / Q000378:metabolism*; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D019289:Pyruvic Acid / Q000378:metabolism*
D064751:Ammonium Compounds; D019344:Lactic Acid; D019289:Pyruvic Acid
FLII12Pglu700μΔ6; laconic; mitoSypHer; peredox; pyronic