(209) Characterization of the Na+/Ca2+ Exchanger (NCS) in Human DRG Neurons

Abstract

Because of the importance of intracellular Ca2+ to processes ranging from protein-interactions to cell death, the concentration of cytosolic Ca2+ ([Ca2+]c) is tightly regulated by a complex array of pumps, transporters, exchangers, and binding proteins. We have recently demonstrated that the Na+/Ca2+ exchanger (NCX), in particular NCX3, plays an important role in attenuating large-increases in [Ca2+]c in a subpopulation of putative nociceptive rat dorsal root ganglion (DRG) neurons. Interestingly, we subsequently demonstrated that inflammation-induced dysregulation of [Ca2+]c in this subpopulation of putative nociceptors was due, at least in part, to a decrease in NCX activity in the sensory neuron cell body. Given the potential importance of this exchanger to nociceptive processing as well as injury-induced changes in nociceptive processing, in the face of a growing list of differences between rodent and human sensory neurons, the purpose of the present study was to characterize NCX activity in human sensory neurons. We employed electrical field stimulation to evoke Ca2+ transients in the presence and absence of LiCl or Choline-Cl bath to block NCX activity. Interestingly, electrical field stimulation of human DRG neurons, at the same parameters used in rat, evoked a much larger Ca2+ transient in both magnitude and duration. We obtained evidence of NCX activity in the majority of neurons tested. Similar to the role of NCX in rat DRG neurons, block of NCX in human DRG neurons increased the duration, but not the magnitude of the electrically evoked Ca2+ transient. However, in contrast to the rat, there appeared to be constitutive NCX activity. Consistent with a number of recent studies, these results highlight potentially important similarities and differences between rodent and human sensory neurons, underscoring the importance of human sensory neurons as a pre-clinical screen of novel therapeutics targeting the primary afferent. Research funded by NIH T32NS073548, 1R01NS083347, and R01DK107966.