Inhibitory modulation of action potentials in crayfish motor axons by fluoxetine

• Published in: Synapse (New York, N.Y.) Vol. 78; no. 4; pp. e22304 - n/a
• Main Authors: Wang, Selene, Lam, Si Seng, Aguilar, Anisah, Ali, Hani, Anakwe, Stephanie, Barahona, Katherine, Hunyadi, Olivia, Jain, Kaahini, Kolodziejski, Derek, Lal, Anindita, Li, Man, MacKenzie, Frank, Miller, John, Nardin, Oliviero, Nguyen, Emily, Pappu, Jaii, Rodriguez, Melissa, Lin, Jen‐Wei
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.07.2024
• Subjects: action potential; Action Potentials - drug effects; Action Potentials - physiology; Animals; Astacoidea - drug effects; Astacoidea - physiology; Axons; Axons - drug effects; Axons - physiology; crayfish; Excitability; Fluoxetine; Fluoxetine - pharmacology; Intracellular; K2P channel; Membrane potential; motor axon; Motor neurons; Motor Neurons - drug effects; Motor Neurons - physiology; neuromuscular junction; synaptic transmission; K2P channel; fluoxetine; neuromuscular junction; crayfish; motor axon; synaptic transmission; action potential
• ISSN: 0887-4476; 1098-2396; 1098-2396
• DOI: 10.1002/syn.22304

The goal of this report is to explore how K2P channels modulate axonal excitability by using the crayfish ventral superficial flexor preparation. This preparation allows for simultaneous recording of motor nerve extracellular action potentials (eAP) and intracellular excitatory junctional potential (EJP) from a muscle fiber. Previous pharmacological studies have demonstrated the presence of K2P‐like channels in crayfish. Fluoxetine (50 µM) was used to block K2P channels in this study. The blocker caused a gradual decline, and eventually complete block, of motor axon action potentials. At an intermediate stage of the block, when the peak‐to‐peak amplitude of eAP decreased to ∼60%–80% of the control value, the amplitude of the initial positive component of eAP declined at a faster rate than that of the negative peak representing sodium influx. Furthermore, the second positive peak following this sodium influx, which corresponds to the after‐hyperpolarizing phase of intracellularly recorded action potentials (iAP), became larger during the intermediate stage of eAP block. Finally, EJP recorded simultaneously with eAP showed no change in amplitude, but did show a significant increase in synaptic delay. These changes in eAP shape and EJP delay are interpreted as the consequence of depolarized resting membrane potential after K2P channel block. In addition to providing insights to possible functions of K2P channels in unmyelinated axons, results presented here also serve as an example of how changes in eAP shape contain information that can be used to infer alterations in intracellular events. This type of eAP‐iAP cross‐inference is valuable for gaining mechanistic insights here and may also be applicable to other model systems. Fluoxetine modulation of AP in unmyelinated axon was studied by analyzing extracellularly recorded AP. Fluoxetine reduced initial charging component (CC) and sodium component (NC) but enhanced the after‐potential component (AFP). These changes suggested the following modulation of intracellular AP: depolarized resting Vm, which became closer to AP threshold, reduced AP amplitude, increased AP duration, which activated a slow K+ current.