Mitochondria and plasma membrane Ca2+‐ATPase control presynaptic Ca2+ clearance in capsaicin‐sensitive rat sensory neurons. (1st March 2013)

• Record Type: Journal Article
• Authors: Shutov, Leonid P.; Kim, Man‐Su; Houlihan, Patrick R.; Medvedeva, Yuliya V.; Usachev, Yuriy M.
• Is Part Of: Journal of physiology. Volume 591:Number 10(2013:May)
• Page Start: 2443
• Page End: 2462
• Publication Date: 2013-03-01
• Subjects: Physiology -- Periodicals; 612.005
• DOI: 10.1113/jphysiol.2012.249219
• Languages: English
• ISSNs: 0022-3751

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Key points</title> <p> <list id="l1" list-type="simple"> <list-item> <label> </label> <p>The first sensory synapse formed between the central processes of primary afferents and dorsal horn neurons plays an important role in controlling the flow of nociceptive information from the periphery to the CNS, and plasticity at this synapse contributes to centrally mediated pain hypersensitivity.</p> </list-item> <list-item> <label> </label> <p>Although exocytosis and synaptic plasticity are regulated by presynaptic Ca<sup>2+</sup>, the mechanisms underlying presynaptic Ca<sup>2+</sup> signalling at the first sensory synapse are not well understood.</p> </list-item> <list-item> <label> </label> <p>In this study we show that the plasma membrane Ca<sup>2+</sup>‐ATPase and mitochondria are the major regulators of presynaptic Ca<sup>2+</sup> signalling in capsaicin‐sensitive dorsal root ganglion neurons accounting for ∼47 and ∼40% of presynaptic Ca<sup>2+</sup> clearance, respectively.</p> </list-item> <list-item> <label> </label> <p>Quantitative analysis of changes in cytosolic and mitochondrial Ca<sup>2+</sup> concentrations demonstrates that the mitochondrial Ca<sup>2+</sup> uniporter is highly sensitive to cytosolic Ca<sup>2+</sup> at this synapse.</p> </list-item> <list-item> <label> </label> <p>These results help us understand presynaptic mechanisms at the first sensory synapse.</p> </list-item> </list> </p> <p> <bold>Abstract </bold> The central processes of primary nociceptors form synaptic connections with the second‐order nociceptive neurons located in the dorsal horn of the spinal cord. These synapses gate the flow of nociceptive information from the periphery to the CNS, and plasticity at these synapses contributes to centrally mediated hyperalgesia and allodynia. Although exocytosis and synaptic plasticity are controlled by Ca<sup>2+</sup> at the release sites, the mechanisms underlying presynaptic Ca<sup>2+</sup> signalling at the nociceptive synapses are not well characterized. We examined the presynaptic mechanisms regulating Ca<sup>2+</sup> clearance following electrical stimulation in capsaicin‐sensitive nociceptors using a dorsal root ganglion (DRG)/spinal cord neuron co‐culture system. Cytosolic Ca<sup>2+</sup> concentration ([Ca<sup>2+</sup>]<sub>i</sub>) recovery following electrical stimulation was well approximated by a monoexponential function with a τ∼2 s. Inhibition of sarco‐endoplasmic reticulum Ca<sup>2+</sup>‐ATPase did not affect presynaptic [Ca<sup>2+</sup>]<sub>i</sub> recovery, and blocking plasmalemmal Na<sup>+</sup>/Ca<sup>2+</sup> exchange produced only a small reduction in the rate of [Ca<sup>2+</sup>]<sub>i</sub> recovery (∼12%) that was independent of intracellular K<sup>+</sup>. However, [Ca<sup>2+</sup>]<sub>i</sub> recovery in presynaptic boutons strongly depended on the plasma membrane Ca<sup>2+</sup>‐ATPase (PMCA) and mitochondria that accounted for ∼47 and 40%, respectively, of presynaptic Ca<sup>2+</sup> clearance. Measurements using a mitochondria‐targeted Ca<sup>2+</sup> indicator, mtPericam, demonstrated that presynaptic mitochondria accumulated Ca<sup>2+</sup> in response to electrical stimulation. Quantitative analysis revealed that the mitochondrial Ca<sup>2+</sup> uptake is highly sensitive to presynaptic [Ca<sup>2+</sup>]<sub>i</sub> elevations, and occurs at [Ca<sup>2+</sup>]<sub>i</sub> levels as low as ∼200–300 n<sc>m</sc>. Using RT‐PCR, we detected expression of several putative mitochondrial Ca<sup>2+</sup> transporters in DRG, such as MCU, Letm1 and NCLX. Collectively, this work identifies PMCA and mitochondria as the major regulators of presynaptic Ca<sup>2+</sup> signalling at the first sensory synapse, and underlines the high sensitivity of the mitochondrial Ca<sup>2+</sup> uniporter in neurons to cytosolic Ca<sup>2+</sup>.</p> </abstract>