Mu-opioid receptors are expressed on pre-Bötzinger pre-inspiratory neurones and are associated with G⍺i.

What would happen to MEMBRANE POTENTIAL of pre-Bötzinger pre-inspiratory neurone following activation of mu-opioid receptors?

Question

Mu-opioid receptors are expressed on pre-Bötzinger pre-inspiratory neurones and are associated with G⍺i.

What would happen to MEMBRANE POTENTIAL of pre-Bötzinger pre-inspiratory neurone following activation of mu-opioid receptors?

BlackTom AI · Accepted Answer

Mu-opioid receptors are Gi/o-protein–coupled receptors that produce neuronal inhibition, so activation leads to a decrease in the neuron's membrane potential (hyperpolarization).

1) Relevant knowledge points and concepts
- Mu-opioid receptors couple to Gαi/Gβγ. Gαi inhibits adenylyl cyclase (↓cAMP, ↓PKA) and Gβγ directly modulates ion channels.  
- Gβγ commonly opens G-protein–activated inwardly rectifying K+ (GIRK) channels and inhibits voltage-gated Ca2+ channels.  
- Opening K+ channels increases K+ conductance (gK), driving the membrane potential toward the K+ equilibrium potential (EK, ≈ −90 mV), producing hyperpolarization and reduced excitability.

2) Step-by-step reasoning
- Mu receptor activation → Gαi and Gβγ freed.  
- Gβγ binds and opens GIRK channels → gK increases substantially.  
- The membrane potential Vm is determined by weighted conductances: Vm ≈ (gK·EK + gL·EL + gNa·ENa + ...)/ (gK + gL + gNa + ...).  
- With a large increase in gK, the numerator and denominator shift Vm closer to EK (more negative).

3) Calculation / intermediate steps (illustrative)
- Suppose initially Vm = −60 mV; EK = −90 mV. With baseline conductances, Vm = −60 mV. If gK doubles or increases markedly, Vm will move toward −90 mV. For example, if after activation the K term dominates: Vm ≈ (0.8·(−90) + 0.2·(−60)) = −84 + (−12) = −96/1 = −84 mV (illustrative), i.e. a decrease of ~24 mV. Exact change depends on channel expression, but direction is hyperpolarizing.

4) Why the correct answer is correct
- Increased K+ conductance and reduced inward Ca2+/Na+ currents hyperpolarize the neuron, lowering (making more negative) its membrane potential and reducing firing of pre-Bötzinger pre‑inspiratory neurons.

5) Why other choices would be incorrect
- “Increase in membrane potential” (depolarization) is incorrect because Gi signaling increases K+ conductance and inhibits Ca2+ influx, not excitatory currents.  
- “No change” is unlikely because GIRK activation produces a clear conductance change that shifts Vm.  
- Any option implying excitation conflicts with known Gi/GIRK physiology.

6) Conclusion
Activation of mu-opioid receptors on pre‑Bötzinger pre‑inspiratory neurons causes hyperpolarization (a decrease in membrane potential), which matches the provided answer: Decrease in membrane potential.

Mu-opioid receptors are expressed on pre-Bötzinger pre-inspiratory neurones and are associated with G⍺i. What would happen to MEMBRANE POTENTIAL of pre-Bötzinger pre-inspiratory neurone following activation of mu-opioid receptors?单项选择题

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