Dynamic Changes in Cytosolic ATP Levels in Cultured Glutamatergic Neurons During NMDA-Induced Synaptic Activity Supported by Glucose or Lactate

Abstract

We have previously shown that synaptic transmission fails in cultured neurons in the presence of lactate as the sole substrate. Thus, to test the hypothesis that the failure of synaptic transmission is a consequence of insufficient energy supply, ATP levels were monitored employing the ATP biosensor Ateam1.03YEMK. While inducing synaptic activity by subjecting cultured neurons to two 30 s pulses of NMDA (30 µM) with a 4 min interval, changes in relative ATP levels were measured in the presence of lactate (1 mM), glucose (2.5 mM) or the combination of the two. ATP levels reversibly declined following NMDA-induced neurotransmission activity, as indicated by a reversible 10-20 % decrease in the response of the biosensor. The responses were absent when the NMDA receptor antagonist memantine was present. In the presence of lactate alone, the ATP response dropped significantly more than in the presence of glucose following the 2nd pulse of NMDA (approx. 10 vs. 20 %). Further, cytosolic Ca(2+) homeostasis during NMDA-induced synaptic transmission is partially inhibited by verapamil indicating that voltage-gated Ca(2+) channels are activated. Lastly, we showed that cytosolic Ca(2+) homeostasis is supported equally well by both glucose and lactate, and that a pulse of NMDA causes accumulation of Ca(2+) in the mitochondrial matrix. In summary, we have shown that ATP homeostasis during neurotransmission activity in cultured neurons is supported by both glucose and lactate. However, ATP homeostasis seems to be negatively affected by the presence of lactate alone, suggesting that glucose is needed to support neuronal energy metabolism during activation.

Monitoring ATP dynamics in electrically active white matter tracts

“…We found that axonal ATP levels were significantly lower during HFS when nerves were incubated with lactate or pyruvate as the sole energy substrate. This suggests that lactate/pyruvate alone does not support ATP production as well as glucose and confirms observations in cultured cerebellar granule cells with repetitive activation of NMDA-receptors (Lange et al, 2015). …”

Activity‐dependent modulation of intracellular ATP in cultured cortical astrocytes

“…More recently, genetically encoded optical sensors for ATP have been introduced that enable the direct study of intracellular ATP levels with high temporal and spatial resolution by fluorescence imaging. These sensors change either their fluorescence or luminescence properties depending on ATP concentration (Imamura et al, 2009;Berg et al, 2009;Nakano et al, 2011;Tantama et al, 2013;Rangaraju et al, 2014) and so far have been mainly used to study neuronal ATP homeostasis and regulation (Connolly et al, 2014;Rangaraju et al, 2014;Toloe et al, 2014;Lange et al, 2015;Pathak et al, 2015). Here, we took advantage of ATeam1.03 YEMK , a fluorescent, FRET-based sensor for ATP (Imamura et al, 2009), to study ATP dynamics in astrocytes during exposure to the neurotransmitters glutamate and dopamine, as well as the effect of different energy substrates (glucose, lactate) on ATP changes in those cells.…”

The Energy Homeostasis Principle: Neuronal Energy Regulation Drives Local Network Dynamics Generating Behavior

“…ATP sources change dynamically with neuronal activity and several mechanisms account for this fine-tuning response. First, neuronal mitochondria are capable of raising ATP synthesis in response to increased synaptic stimuli (Jekabsons and Nicholls 2004;Connolly et al 2014;Toloe et al 2014;Lange et al 2015;Rangaraju, Calloway, and Ryan 2014). Although the molecular meditators for this activation are not completely elucidated, the increase of the respiratory rate of an isolated mitochondria correlates well with the ADP concentration (G. C. Brown 1992), and neuronal mitochondrial function has been satisfactorily modeled considering the changes in ATP and ADP levels (Berndt, Kann, and Holzhütter 2015).…”

“…Several evidences demonstrate that it is reasonable to assume a constant value for energy availability for neurons over the long term (energetic homeostasis). For instance, cultured neurons exhibit a steady value for free adenosine triphosphate (ATP) in basal conditions, which transiently decrease during the induction of glutamatergic synaptic activity through various energy challenges (Marcaida et al 1997;Marcaida et al 1995;Lange et al 2015;Rangaraju, Calloway, and Ryan 2014). This tight energy management suggests a relevant role for neuronal energy homeostasis on neuronal and network functional properties.…”