Divergent effects of painful nerve injury on mitochondrial Ca2+ buffering in axotomized and adjacent sensory neurons

Abstract

Mitochondria critically regulate cytoplasmic Ca2+ concentration ([Ca2+]c), but the effects of sensory neuron injury have not been examined. Using FCCP (1μM) to eliminate mitochondrial Ca2+ uptake combined with oligomycin (10μM) to prevent ATP depletion, we first identified features of depolarization-induced neuronal [Ca2+]c transients that are sensitive to blockade of mitochondrial Ca2+ buffering in order to assess mitochondrial contributions to [Ca2+]c regulation. This established the loss of a shoulder during the recovery of the depolarization (K+)-induced transient, increased transient peak and area, and elevated shoulder level as evidence of diminished mitochondrial Ca2+ buffering. We then examined transients in Control neurons and neurons from the 4th lumbar (L4) and L5 dorsal root ganglia after L5 spinal nerve ligation (SNL). The SNL L4 neurons showed decreased transient peak and area compared to control neurons, while the SNL L5 neurons showed increased shoulder level. Additionally, SNL L4 neurons developed shoulders following transients with lower peaks than Control neurons. Application of FCCP plus oligomycin elevated resting [Ca2+]c in SNL L4 neurons more than in Control neurons. Whereas application of FCCP plus oligomycin 2s after neuronal depolarization initiated mitochondrial Ca2+ release in most Control and SNL L4 neurons, this usually failed to release mitochondrial Ca2+ from SNL L5 neurons. For comparable cytoplasmic Ca2+ loads, the releasable mitochondrial Ca2+ in SNL L5 neurons was less than Control while it was increased in SNL L4 neurons. These findings show diminished mitochondrial Ca2+ buffering in axotomized SNL L5 neurons but enhanced Ca2+ buffering by neurons in adjacent SNL L4 neurons.

Etiology and Pharmacology of Neuropathic Pain

“…This altered activity results from changes in the properties and/or expression of various types of voltage-gated Na + , K + , and Ca 2+ channels (Waxman et al, 1999;Abdulla andSmith, 2001b, 2002;Cummins et al, 2001;Stemkowski and Smith, 2012b;Bourinet et al, 2014;Waxman and Zamponi, 2014;Daou et al, 2016). There are also changes in the function of Na + -K + ATPases (Venteo et al, 2016), intracellular Ca 2+ handling (Hogan et al, 2014;D'Arco et al, 2015;Yilmaz and Gold, 2016;Yilmaz et al, 2017), TRP channels (Basso and Altier, 2017), and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels (Hogan and Poroli, 2008;Emery et al, 2011;Noh et al, 2014;Young et al, 2014).…”

Paclitaxel-induced increase in mitochondrial volume mediates dysregulation of intracellular Ca2+ in putative nociceptive glabrous skin neurons from the rat

“…Mitochondrial Ca 2+ uptake depends on an intact mitochondrial membrane potential and uncouplers such as CCCP and FCCP are widely used to diminish the Ca 2+ uptake into these organelles [27]. To block mitochondrial Ca 2+ uptake without ATP depletion due to the membrane potential loss-induced reversal of the ATP synthase [28], we applied the uncoupler CCCP (10 μM) together with ATP synthase inhibitor oligomycin (10 μM) (Fig. 2C).…”

Mitochondria and sensory processing in inflammatory and neuropathic pain

“…Mitochondria are a major regulator of Ca 2+ signaling at the first sensory synapse ( 39 , 76 , 174 , 177 , 178 ). Moreover, mitochondrial Ca 2+ mediates signaling to the nucleus and the release of death signals, in case of very high Ca 2+ ( 39 , 75 , 76 , 174 , 177 , 179 – 181 ).…”

“…Nerve damage causes disturbed mitochondrial Ca 2+ buffering ( 180 ). For example, spinal nerve ligation in rats reduced mitochondrial Ca 2+ storage capacity in lumbar DRG neurons ( 75 ). Rats with chemotherapy-induced neuropathic pain have a decreased duration of depolarization-evoked Ca 2+ transient, which is partially mediated by an augmented mitochondrial Ca 2+ uptake and increased mitochondrial volume ( 78 ).…”