Store-operated calcium entry in vagal sensory nerves is independent of Orai channels

Abstract

Vagal sensory nerves innervate the majority of visceral organs (e.g. heart, lungs, GI tract, etc) and their activation is critical for defensive and regulatory reflexes. Intracellular Ca2+ is a key regulator of neuronal excitability and is largely controlled by the Ca2+ stores of the endoplasmic reticulum. In other cell types store-operated channels (SOC) have been shown to contribute to the homeostatic control of intracellular Ca2+. Here, using Ca2+ imaging, we have shown that ER depletion in vagal sensory neurons (using thapsigargin or caffeine) in the absence of extracellular Ca2+ evoked Ca2+ influx upon reintroduction of Ca2+ into the extracellular buffer. This store-operated Ca2+ entry (SOCE) was observed in approximately 25–40% of vagal neurons, equally distributed among nociceptive and non-nociceptive sensory subtypes. SOCE was blocked by Gd3+ but not by the Orai channel blocker SKF96365. We found Orai channel mRNA in extracts from whole vagal ganglia, but when using single cell RT-PCR analysis we found only 3 out of 34 neurons expressed Orai channel mRNA, indicating that Orai channel expression in the vagal ganglia was likely derived from non-neuronal cell types. Confocal microscopy of vagal neurons in 3 day cultures demonstrated rich ER tracker fluorescence throughout axonal and neurite structures and ER store depletion (thapsigargin) evoked Ca2+ transients from these structures. However, no SOCE could be detected in the axonal/neurite structures of vagal neurons. We conclude that SOCE occurs in vagal sensory neuronal cell bodies through non-Orai mechanisms but is absent at nerve terminals.

Neuronal SOCE: Myth or Reality?

“…Figure 1D), as now documented by several groups in different types of neurons [4][5][6][7][8]. In fact, depletion of ER and cytoplasmic Ca 2+ is so fast that it partially occludes or masks thapsigargin-mediated ER Ca 2+ release ( Figure 1C).…”

STIM1 and STIM2 Proteins Differently Regulate Endogenous Store-operated Channels in HEK293 Cells

“…However, it is only in a few cell types (mainly in the immune system) that store-operated calcium currents are mediated by CRAC channels alone. Most other cells contain store-operated calcium channels of different types (2, 34 -37), and CRAC channels may even be absent (38). For example, we have revealed four different store-operated channel types in the A431 cell line (39,40).…”

Oxidative stress as activators of sensory nerves for cough

“…Mitochondria can also be observed in axonal terminals of vagal neurons in long-term culture [54]. In order to further understand the functional effect of increased mitochondrial ROS on airway afferent, we have used specific inhibitors of the mitochondrial electron transfer chain.…”