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mu-Opioid receptor activation reduces multiple components of high-threshold calcium current in rat sensory neurons
1Department of Physiology, University of Michigan, Ann Arbor 48109-0622, USA.
Abstract:
Whole-cell patch-clamp recordings were used to characterize calcium channel types that are modulated by mu-opioid receptor activation in rat dorsal root ganglion (DRG) neurons. Five distinct components of high-threshold calcium current were isolated on the basis of their sensitivity to the selective channel blockers omega-conotoxin GVIA, nifedipine, omega-conotoxin MVIIC, or omega-agatoxin IVA. The mu-opioid selective agonist Tyr-Pro-NMePhe-D-Pro-NH2 (PLO17) routinely suppressed high-threshold currents and this effect was always reduced by omega-conotoxin GVIA. A fraction of PLO17-sensitive current remained after omega-conotoxin GVIA that was eliminated by application of omega-agatoxin IVA alone or in combination with omega-conotoxin MVIIC. Nifedipine had no effect on mu-opioid responses nor did PLO17 affect the slow component of tail current induced by Bay K 8644. These data suggest that mu-opioid receptors are negatively coupled to three types of calcium channels in rat DRG neurons, including an omega-conotoxin GVIA-sensitive (N-type) channel, an omega-agatoxin IVA-sensitive (P-type) channel and an omega-conotoxin MVIIC-sensitive, nifedipine/GVIA/omega-Aga IVA-resistant (presumptive Q-type) channel.
Insights
Mu-opioid receptors modulate calcium channels in rat dorsal root ganglion neurons. Activation suppresses N-type, P-type, and Q-type calcium currents, impacting pain signaling pathways.
Area of Science:
- Neuroscience
- Pharmacology
- Molecular Biology
Background:
- Mu-opioid receptors (MORs) are key targets for pain management.
- Calcium channels play critical roles in neuronal excitability and neurotransmitter release.
- Understanding MOR modulation of specific calcium channel subtypes is crucial for developing targeted analgesics.
Purpose of the Study:
- To identify the specific high-threshold calcium channel types modulated by mu-opioid receptor activation in rat dorsal root ganglion (DRG) neurons.
- To elucidate the coupling mechanisms between MORs and distinct calcium channel subtypes.
Main Methods:
- Whole-cell patch-clamp electrophysiology was employed to record calcium currents in rat DRG neurons.
- Selective calcium channel blockers (omega-conotoxin GVIA, nifedipine, omega-conotoxin MVIIC, omega-agatoxin IVA) were used to isolate current components.
- The effects of a selective MOR agonist (PLO17) on these isolated currents were characterized.
Main Results:
- Mu-opioid receptor activation by PLO17 suppressed high-threshold calcium currents.
- This suppression was primarily mediated by blockade of omega-conotoxin GVIA-sensitive (N-type) channels.
- A residual current sensitive to omega-agatoxin IVA (P-type) and omega-conotoxin MVIIC (presumptive Q-type) was also modulated by MOR activation.
Conclusions:
- Mu-opioid receptors are negatively coupled to at least three distinct calcium channel types in rat DRG neurons: N-type, P-type, and a presumptive Q-type.
- This differential coupling provides a molecular basis for the complex effects of opioids on neuronal excitability and pain perception.
- Targeting specific calcium channel subtypes modulated by MORs may offer novel strategies for pain relief with reduced side effects.