Fentanyl Decreases Ca2+Currents in a Population of Capsaicin-responsive Sensory Neurons

Background Neuraxial opioids produce analgesia in part by decreasing excitatory neurotransmitter release from primary nociceptive neurons, an effect that may be due to inhibition of presynaptic voltage-activated Ca2+ channels. The purpose of this study was to determine whether opioids decrease Ca2+ currents (I Ca ) in primary nociceptive neurons, identified by their response to the algogenic agent capsaicin. Methods I was recorded from acutely isolated rat dorsal root ganglion neurons using the whole cell patch clamp technique before, during, and after application of the micro -opioid agonist fentanyl (0.01-1 micro m). Capsaicin was applied to each cell at the end of the experiment. Results Fentanyl reduced I Ca in a greater proportion of capsaicin-responsive cells (62 of 106, 58%) than capsaicin-unresponsive cells (2 of 15, 13%; P < 0.05). Among capsaicin-responsive cells, the decrease in I Ca was 38 +/- 3% (n = 36, 1 micro m) in fentanyl-sensitive cells just 7 +/- 1% (n = 15, 1 micro m; P < 0.05) in fentanyl-insensitive cells. Among capsaicin-responsive cells, I Ca inactivated more rapidly in fentanyl-sensitive cells (tau, 52 +/- 4 ms, n = 22) than in fentanyl-insensitive cells (93 +/- 14 ms, n = 24; P < 0.05). This was not due to differences in the types of Ca2+ channels expressed as the magnitudes of omega-conotoxin GVIA-sensitive (N-type), nifedipine-sensitive (L-type), and GVIA/nifedipine-resistant (primarily P-/Q-type) components of I Ca were similar. Conclusions The results show that opioid-sensitive Ca2+ channels are expressed by very few capsaicin-unresponsive neurons but by more than half of capsaicin-responsive neurons. The identity of the remaining capsaicin-responsive (and therefore presumed nociceptive) neurons that express opioid-insensitive Ca2+ channels is unknown but may represent a potential target of future non-opioid-based therapies for acute pain.

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P2X Receptor–Mediated Ionic Currents in Dorsal Root Ganglion Neurons

Journal of Neurophysiology ◽

10.1152/jn.1999.82.3.1590 ◽

1999 ◽

Vol 82 (3) ◽

pp. 1590-1598 ◽

Cited By ~ 118

Author(s):

Edward C. Burgard ◽

Wende Niforatos ◽

Tim van Biesen ◽

Kevin J. Lynch ◽

Edward Touma ◽

...

Keyword(s):

Dorsal Root ◽

Slow Component ◽

Ionic Currents ◽

P2x Receptors ◽

Fast Component ◽

Dorsal Root Ganglion Neurons ◽

P2x Receptor ◽

Receptor Subtype ◽

Nociceptive Neurons ◽

Ganglion Neurons

Nociceptive neurons in the dorsal root ganglia (DRG) are activated by extracellular ATP, implicating P2X receptors as potential mediators of painful stimuli. However, the P2X receptor subtype(s) underlying this activity remain in question. Using electrophysiological techniques, the effects of P2X receptor agonists and antagonists were examined on acutely dissociated adult rat lumbar DRG neurons. Putative P2X-expressing nociceptors were identified by labeling neurons with the lectin IB4. These neurons could be grouped into three categories based on response kinetics to extracellularly applied ATP. Some DRG responses (slow DRG) were relatively slowly activating, nondesensitizing, and activated by the ATP analogue α,β-meATP. These responses resembled those recorded from 1321N1 cells expressing recombinant heteromultimeric rat P2X2/3 receptors. Other responses (fast DRG) were rapidly activating and desensitized almost completely during agonist application. These responses had properties similar to those recorded from 1321N1 cells expressing recombinant rat P2X3 receptors. A third group (mixed DRG) activated and desensitized rapidly (P2X3-like), but also had a slow, nondesensitizing component that functionally prolonged the current. Like the fast component, the slow component was activated by both ATP and α,β-meATP and was blocked by the P2X antagonist TNP-ATP. But unlike the fast component, the slow component could follow high-frequency activation by agonist, and its amplitude was potentiated under acidic conditions. These characteristics most closely resemble those of rat P2X2/3 receptors. These data suggest that there are at least two populations of P2X receptors present on adult DRG nociceptive neurons, P2X3 and P2X2/3. These receptors are expressed either separately or together on individual neurons and may play a role in the processing of nociceptive information from the periphery to the spinal cord.

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Interaction of opioids and membrane potential to modulate Ca2+ channels in rat dorsal root ganglion neurons

Journal of Neurophysiology ◽

10.1152/jn.1995.73.5.1793 ◽

1995 ◽

Vol 73 (5) ◽

pp. 1793-1798 ◽

Cited By ~ 22

Author(s):

M. D. Womack ◽

E. W. McCleskey

Keyword(s):

Dorsal Root Ganglion ◽

Sensory Neurons ◽

Action Potentials ◽

Dorsal Root ◽

Dorsal Root Ganglion Neurons ◽

High Threshold ◽

Partial Recovery ◽

Drg Neurons ◽

Ganglion Neurons ◽

Ca2 Channels

1. Using patch-clamp methods, we show that brief prepulses to very positive voltages increase (facilitate) the amplitude of current through Ca2+ channels during a subsequent test pulse in some, but not all, dorsal root ganglion (DRG) sensory neurons. The amplitude of this facilitated current generally increases when the Ca2+ channels are inhibited by activation of the mu-opioid receptor. 2. The facilitated current is blocked by omega-conotoxin GVIA, activates in the range of high-threshold Ca2+ channels, and inactivates at relatively negative holding voltages. Thus facilitated current passes through N-type Ca2+ channels, the same channels that are inhibited by opioids and control neurotransmitter release in sensory neurons. 3. Although maximal facilitation occurs only at unphysiologically high membrane potentials (above +100 mV), some facilitation is seen after prepulses to voltages reached during action potentials. After return to the holding potential, facilitation persists for hundreds of milliseconds, considerably longer than in other neurons. Brief trains of pulses designed to mimic action potentials caused small facilitation (19% of maximal) in a fraction (8 of 24) of opioid-inhibited neurons. 4. We conclude that 1) prepulses to extremely positive voltages can cause partial recovery of Ca2+ channels inhibited by opioids; and 2) small, but detectable, facilitation is also seen after physiological stimulation in some DRG neurons. Facilitation, largely considered a biophysical epiphenomenon because of the extreme voltages used to induce it, appears to be physiologically relevant during opioid inhibition of Ca2+ channels in DRG neurons.

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Neurotransmitter release from growth cones of rat dorsal root ganglion neurons in culture

Neuroscience ◽

10.1016/s0306-4522(96)00465-4 ◽

1997 ◽

Vol 77 (4) ◽

pp. 1187-1199 ◽

Cited By ~ 25

Author(s):

H Soeda ◽

H Tatsumi ◽

Y Katayama

Keyword(s):

Dorsal Root Ganglion ◽

Neurotransmitter Release ◽

Dorsal Root ◽

Growth Cones ◽

Dorsal Root Ganglion Neurons ◽

Ganglion Neurons

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Slow sodium conductances of dorsal root ganglion neurons: intraneuronal homogeneity and interneuronal heterogeneity

Journal of Neurophysiology ◽

10.1152/jn.1994.72.6.2796 ◽

1994 ◽

Vol 72 (6) ◽

pp. 2796-2815 ◽

Cited By ~ 93

Author(s):

M. A. Rizzo ◽

J. D. Kocsis ◽

S. G. Waxman

Keyword(s):

Dorsal Root Ganglion ◽

Dorsal Root ◽

Dorsal Root Ganglion Neurons ◽

Half Time ◽

Drg Neurons ◽

Patch Clamp Technique ◽

Adult Rat ◽

Voltage Dependent ◽

Order Of Magnitude ◽

Ganglion Neurons

1. Voltage-dependent Na+ conductances were studied in small (18-25 microns diam) adult rat dorsal root ganglion (DRG) neurons with the use of the whole cell patch-clamp technique. Na+ currents were also recorded from larger (44-50 microns diam) neurons and compared with those of the small neurons. 2. The predominant Na+ conductance in the small neurons was selective over tetramethylammonium by at least 10-fold and was resistant to 1 microM external tetrodotoxin (TTX). Na+ conductances in many larger DRG neurons were kinetically faster and, in contrast, were blocked by 1 microM TTX. 3. The Na+ conductance in the small neurons was kinetically slow. Activation half-times were voltage dependent and ranged from 2 ms at -20 mV to 0.7 ms at +50 mV. Approximately 50% of the activation half-time was comprised of an initial delay. Inactivation half-times were voltage dependent and ranged from 11 ms at -20 mV to 2 ms at +50 mV. 4. Peak slow Na+ conductances were near maximal with conditioning potentials negative to -120 mV and were significantly reduced or eliminated with conditioning potentials positive to -40 mV. The slow Na+ conductance increased gradually with test potentials extending from -40 to +40 mV. In some cells the conductance could be saturated at +10 mV. Peak conductance/voltage relationships, although stable in a given neuron, revealed marked variability among neurons, spanning > 20- and 50-mV domains for steady-state activation and inactivation (current availability), respectively. 5. Kinetics remained stable within a given neuron over the course of an experiment. However, considerable kinetic variation was exhibited from neuron to neuron, such that the half-times of activation and of inactivation spanned an order of magnitude. In all small neurons studied there appeared to be a singular kinetic component of the current, based on sensitivity to the conditioning potential, voltage dependence of activation, and inactivation half-time. 6. Unique closing properties were exhibited by Na+ channels of the small neurons. Hyperpolarization following a depolarization-induced fully inactivated state resulted in tail currents that appeared to be the consequence of reactivation of the slow Na+ conductance. Tail currents recorded at various times during a fixed level of depolarization revealed that the underlying channels accumulated into a volatile inactivated state over the course of the preceding depolarization.(ABSTRACT TRUNCATED AT 400 WORDS)

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Activity and Ca2+ regulate the mobility of TRPV1 channels in the plasma membrane of sensory neurons

eLife ◽

10.7554/elife.03819 ◽

2015 ◽

Vol 4 ◽

Cited By ~ 8

Author(s):

Eric N Senning ◽

Sharona E Gordon

Keyword(s):

Plasma Membrane ◽

Sensory Neurons ◽

Dorsal Root ◽

Optical Recording ◽

Dorsal Root Ganglion Neurons ◽

Mechanical Stimuli ◽

Channel Activation ◽

Trpv1 Channels ◽

Ganglion Neurons ◽

Ca2 Channels

TRPV1 channels are gated by a variety of thermal, chemical, and mechanical stimuli. We used optical recording of Ca2+ influx through TRPV1 to measure activity and mobility of single TRPV1 molecules in isolated dorsal root ganglion neurons and cell lines. The opening of single TRPV1 channels produced sparklets, representing localized regions of elevated Ca2+. Unlike sparklets reported for L-type Ca2+ channels, TRPV4 channels, and AchR channels, TRPV1 channels diffused laterally in the plasma membrane as they gated. Mobility was highly variable from channel-to-channel and, to a smaller extent, from cell to cell. Most surprisingly, we found that mobility decreased upon channel activation by capsaicin, but only in the presence of extracellular Ca2+. We propose that decreased mobility of open TRPV1 could act as a diffusion trap to concentrate channels in cell regions with high activity.

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Modulation of Voltage-Activated Calcium Currents by Mechanical Stimulation in Rat Sensory Neurons

Journal of Neurophysiology ◽

10.1152/jn.1998.80.4.1647 ◽

1998 ◽

Vol 80 (4) ◽

pp. 1647-1652 ◽

Cited By ~ 6

Author(s):

Yona Bouskila ◽

Hugh Bostock

Keyword(s):

Action Potential ◽

Sensory Neurons ◽

Mechanical Stimulation ◽

Action Potential Duration ◽

Calcium Currents ◽

Dorsal Root Ganglion Neurons ◽

Patch Clamp Technique ◽

Whole Cell Patch Clamp ◽

Low Threshold ◽

Ganglion Neurons

Bouskila, Yona and Hugh Bostock. Modulation of voltage-activated calcium currents by mechanical stimulation in rat sensory neurons. J. Neurophysiol. 80: 1647–1652, 1998. We examined the effects of mechanical stress, induced by a stream of bath solution, on evoked action potentials, electrical excitability, and Ca2+ currents in rat dorsal root ganglion neurons in culture with the use of the whole cell patch-clamp technique. Action-potential duration was altered reversibly by flow in 39% of the 51 neurons tested, but membrane potential and excitability were unaffected. The flow-induced increases and decreases in action-potential duration were consistent with the different effects of flow on two types of Ca2+ channel, determined by voltage-clamp recordings of Ba2+ currents. Current through ω-conotoxin–sensitive (N-type) Ca2+ channels increased by an estimated 74% with flow, corresponding to 23% increase in the total high voltage–activated current, whereas current through low-threshold voltage-activated (T-type) channels decreased by 14%. We conclude that modulation of voltage-activated Ca2+ currents constitutes a route by which mechanical events can regulate Ca2+ influx in sensory neurons.

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