M channel enhancers and physiological M channel block

Area of Science:

• Neuroscience
• Pharmacology

Background:

• M-type (Kv7, KCNQ) K(+) channels regulate neuronal resting membrane potential, particularly in nociceptors.
• M-channel enhancers are potential analgesics, but inflammation can inhibit these channels via phospholipase C, contributing to inflammatory pain.

Purpose of the Study:

• To investigate if M-channel enhancers can overcome phospholipase C-mediated inhibition of M-channels in nociceptive sensory neurons.
• To evaluate the efficacy of four M-channel enhancers (retigabine, flupirtine, zinc pyrithione, H(2)O(2)) against PIP(2) depletion and Ca(2+)/calmodulin-induced inhibition.

Main Methods:

• Studied overexpressed Kv7.2/Kv7.3 heteromers and native M currents in dorsal root ganglion neurons.
• Assessed the ability of M-channel enhancers to counteract inhibition induced by phosphatidylinositol 4,5-bisphosphate (PIP(2)) depletion and increased intracellular Ca(2+).

Main Results:

• All enhancers exhibited dual effects: negative voltage dependence shift and increased maximal current, with varying efficacy.
• PIP(2) depletion and Ca(2+)/calmodulin reduced M current amplitude, but enhancers restored activity near the -60 mV threshold.
• Enhancers' efficacy at saturating voltages (0 mV) was more variable, but retigabine and flupirtine maintained efficacy in hyperpolarizing resting membrane potential.

Conclusions:

• M-channel enhancers can overcome PIP(2) and Ca(2+)-calmodulin-induced inhibition of Kv7.2/7.3 channels, particularly at voltages near action potential firing threshold (-60 mV).
• The ability of an enhancer to shift M-channel voltage dependence of activation is crucial for restoring function in sensory neurons during inflammation.