Modulators of Calcium Influx Regulate Membrane Excitability in Rat Dorsal Root Ganglion Neurons (original) (raw)
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Modulators of Calcium Influx Regulate Membrane Excitability in Rat Dorsal Root
Background-Chronic neuropathic pain resulting from neuronal damage remains difficult to treat, in part due to incomplete understanding of underlying cellular mechanisms. We have previously shown that inward Ca 2+ flux (I Ca ) across the sensory neuron plasmalemma is decreased in a rodent model of chronic neuropathic pain, but the direct consequence of this loss of I Ca on function of the sensory neuron has not been defined. We therefore examined the extent to which altered membrane properties after nerve injury, especially increased excitability that may contribute to chronic pain, are attributable to diminished Ca 2+ entry.
Anesthesia and Analgesia, 2008
We have previously shown that a decrease of inward Ca 2+ flux (I Ca ) across the sensory neuron plasmalemma, such as happens after axotomy, elevates neuronal excitability. From this, we predicted that increasing I Ca in injured neurons should correct their hyperexcitability, which we have tested during recording from A-type neurons in non-dissociated dorsal root ganglia after spinal nerve ligation, using an intracellular recording technique. When bath Ca 2+ level was elevated to promote I Ca , the afterhyperpolarization was decreased and repetitive firing was suppressed, which also followed amplification of Ca 2+ -activated K + current with selective agents NS1619 and NS309. Lowered external bath Ca 2+ concentration had opposite effects, similar to previous observations in uninjured neurons. These findings indicate that at least a part of the hyperexcitability of somatic sensory neurons after axotomy is attributable to diminished inward Ca 2+ flux, and that measures to restore I Ca may potentially be therapeutic for painful peripheral neuropathy.
Loss of T-type Calcium Current in Sensory Neurons of Rats with Neuropathic Pain
Anesthesiology, 2003
Background Pathophysiology in the primary sensory neuron may contribute to chronic neuropathic pain. Ca channels play a central role in neuronal processes, and sensory neurons are rich in low-voltage-activated calcium channels (LVACCs). However, the physiologic function of these channels is unknown. Their possible role in rebound burst firing makes them a candidate for increased excitability after neuropathic injury. Methods This study uses pharmacological methods to isolate LVACC in cells from the dorsal root ganglia of neuropathic and sham-operated rats, including the blockade of high-voltage-activated Ca channels with fluoride and selective toxins. LVACCs were examined with conventional whole cell patch clamp electrophysiology techniques. Results After chronic constriction injury of the peripheral axon, LVACC was significantly reduced compared to sham rats as shown by a 60% reduction in peak current density and an 80% reduction in total calcium influx. A depolarizing shift in the...
Store-Operated Ca2+ Entry in Sensory Neurons: Functional Role and the Effect of Painful Nerve Injury
Journal of Neuroscience, 2011
Painful nerve injury disrupts levels of cytoplasmic and stored Ca 2ϩ in sensory neurons. Since influx of Ca 2ϩ may occur through store-operated Ca 2ϩ entry (SOCE) as well as voltage-and ligand-activated pathways, we sought confirmation of SOCE in sensory neurons from adult rats and examined whether dysfunction of SOCE is a possible pathogenic mechanism. Dorsal root ganglion neurons displayed a fall in resting cytoplasmic Ca 2ϩ concentration when bath Ca 2ϩ was withdrawn, and a subsequent elevation of cytoplasmic Ca 2ϩ concentration (40 Ϯ 5 nM) when Ca 2ϩ was reintroduced, which was amplified by store depletion with thapsigargin (1 M), and was significantly reduced by blockers of SOCE, but was unaffected by antagonists of voltage-gated membrane Ca 2ϩ channels. We identified the underlying inwardly rectifying Ca 2ϩ -dependent I CRAC (Ca 2ϩ release activated current), as well as a large thapsigargin-sensitive inward current activated by withdrawal of bath divalent cations, representing SOCE. Molecular components of SOCE, specifically STIM1 and Orai1, were confirmed in sensory neurons at both the transcript and protein levels. Axonal injury by spinal nerve ligation (SNL) elevated SOCE and I CRAC . However, SOCE was comparable in injured and control neurons when stores were maximally depleted by thapsigargin, and STIM1 and Orai1 levels were not altered by SNL, showing that upregulation of SOCE after SNL is driven by store depletion. Blockade of SOCE increased neuronal excitability in control and injured neurons, whereas injured neurons showed particular dependence on SOCE for maintaining levels of cytoplasmic and stored Ca 2ϩ , which indicates a compensatory role for SOCE after injury.
Calcium dependence of axotomized sensory neurons excitability
Neuroscience Letters, 2005
Hyperexcitability of axotomized dorsal root ganglion neurons is thought to play a role in neuropathic pain. Numerous changes in ionic channels expression or current amplitude are reported after an axotomy, but to date no direct correlation between excitability of axotomized sensory neurons and ionic channels alteration has been provided. Following sciatic nerve injury, we examined, under whole-cell patch clamp recording, the effects of calcium homeostasis on the electrical activity of axotomized medium-sized sensory neurons isolated from lumbar dorsal root ganglia of adult mice. Axotomy induced an increase in excitability of medium sensory neurons among which 25% develop a propensity to fire repetitively. The condition necessary to get burst discharge in axotomized neurons was the presence of a high intracellular Ca2+ buffer concentration. The main effect was to amplify the increase in threshold current and apparent input resistance induced by axotomy. These data supply evidence for a role of Ca2+-dependent mechanisms in the control of excitability of axotomized sensory neurons.
Journal of Neuroscience Research, 1993
Whole cell currents evoked by pain-inducing agents-bradykinin (Bk), capsaicin (Cap), and reciniferatoxin (RTX), and their modulation of voltageactivated Ca currents were examined in F-11 cells using a patch electrode voltage clamp technique. Most F-11 cells generated action potentials under current clamp if their membrane potentials were held sufficiently negative. Average peak inward Na current (INa) was 100 pA/cm2 and the Z , , was abolished by loM6 M tetrodotoxin. At least two types of Ca currents could be clearly distinguished on the basis of voltage dependency and kinetics; a low threshold transient ZCa(t) and a high threshold sustained ZCa(,). In addition, another high threshold transient Ca current, presumably was observed. About 30% of the cells produced inward current for these pain-inducing agents, when activated at the membrane holding potential of-70 mV. In some F-11 cells, the amplitude of action potential was observed to increase during M Cap-induced depolarization. Both low and high threshold Ca currents were reduced by M Bk in the majority of the cells. Similarly, both M Cap and lop9 M RTX reduced these Ca currents. However, a considerable number of cells showed an initial enhancement followed by reduction in the amplitude of these Ca currents. With higher concentrations of these ligands, all Ca currents were suppressed. Such modulation of voltage-activated Ca currents by pain-inducing agents occurred in both the presence and absence of apparent receptor-activated current flows in the cells. In pertussis toxin (PTX)treated cells, the inhibitory modulation of Ca currents by pain-inducing agents was suppressed. In contrast, in cholera toxin (CTX)-treated cells, this inhibitory modulation appeared to be enhanced. These data indicate that the inhibitory modulation of Ca channel currents by Cap and RTX, similarly to that of Bk, involves a PTX-sensitive inhibitory G protein (Gi).
Depletion of Calcium Stores in Injured Sensory Neurons
Anesthesiology, 2009
Background-Painful nerve injury leads to disrupted Ca 2+ signaling in primary sensory neurons, including decreased endoplasmic reticulum (ER) Ca 2+ storage. The present study examines potential causes and functional consequences of Ca 2+ store limitation after injury.
Experimental Brain Research, 2002
Previous studies have shown that spinal L-type, N-type, and P-type Ca 2+ -channel blockers are effective in modulating pain behavior caused nerve injury. In the present work, using the loose ligation of the sciatic nerve model, we characterized the time course of the appearance of tactile and cold allodynia and the corresponding spinal expression of the N-type Ca 2+ channel a 1B -subunit after nerve ligation. Within 1 week after ligation, the majority of rats developed a unilateral sensitivity to mechanical stimulation (von Frey filaments), as well as sensitivity to cold, which persisted for 30 days. Immunocytochemical analysis of the spinal cord in shamoperated animals for the a 1B -subunit showed a smooth, moderate staining pattern in the superficial laminae I-II, as well as in ventral a-motoneurons. In nerve-ligated animals, an intense, dot-like immunoreactivity in the ipsilateral dorsal horn was observed from 5-20 days after nerve ligation. The most prominent a 1B -subunit upregulation was found in the outer as well as the inner part of lamina II (II o , II i ), extending from the medial toward the lateral region of the L4 and L5 spinal segments. The behavioral changes which developed after chronic constriction injury directly correlated with the a 1B -subunit upregulation in the corresponding spinal cord segments. These data suggest that upregulation of the spinal a 1Bsubunit may play an important role in the initiation and maintenance of pain state after peripheral nerve injury.
Painful Neuropathy Decreases Membrane Calcium Current in Mammalian Primary Afferent Neurons
Journal of the Peripheral Nervous System, 2000
In this study, differences of unmyelinated nerve fiber density in sural nerve biopsy material from patients suffering from neuropathies of unknown origin with (n ϭ 14) or without pain (n ϭ 13) were analyzed. Immunocytochemistry was applied to differentiate afferent sensory and efferent sympathetic nerve fibers. All patients were evaluated for deficits of small fiber function with thermotesting, quantitative sudomotor-axon reflextesting and testing of painfulness of mechanical stimuli before performing the biopsy. No difference was found between patients with and without pain concerning clinical deficits or results in any of the neurophysiological examinations. There were also no histopathological differences concerning the density of afferent C-fibers. However, absolute and relative density of efferent sympathetic nerve fibers was significantly higher in patients with painful neuropathy (P Ͻ 0.001), although none of the patients demonstrated clinical sympathetic abnormalities. We conclude that an imbalance between afferent and sympathetic nerve fiber density in the periphery may contribute to neuropathic pain even in those patients without obvious clinical autonomic disturbances.
Calcium-dependent chloride current induced by axotomy in rat sympathetic neurons.
The Journal of physiology, 1994
1. Seven to ten days after sectioning their axons, rat sympathetic neurons were studied using intracellular recording techniques in an in vitro preparation of the superior cervical ganglion. 2. In 75 % of axotomized cells, an after-depolarization (ADP) was observed following spike firing or depolarization with intracellular current pulses. Discontinuous single-electrode voltage-clamp techniques were employed to study the ADP. When the membrane potential was clamped at the resting level just after an action potential, a slow inward current wa.s recorded in cells that showed an ADP. 3. In the presence of ITX and TEA, inward peaks and outward currents were recorded during depolarizing voltage jumps, followed by slowly decaying inward tail currents accompanied by large increases in membrane conductance. The inward peak and tail currents activated between -10 and -20 mV and reached maximum amplitudes around 0 mV. With depolarizing jumps to between +40 and +50 mV, net outward currents were recorded during the depolarizing jumps but inward tail currents were still activated. 4. In the presence of the Ca2+ channel blocker cadmium, or when Ca2+ was substituted by Mg2+, the ADP disappeared. In voltage-clamped cells, cadmium blocked the inward tail currents. The reversal potential for the inward tail current was approximately -15 mV.