Transient Receptor Potential Vanilloid 4 Activation-Induced Increase in Glycine-Activated Current in Mouse Hippocampal Pyramidal Neurons

Background/Aims: Glycine plays an important role in regulating hippocampal inhibitory/ excitatory neurotransmission through activating glycine receptors (GlyRs) and acting as a co-agonist of N-methyl-d-aspartate-type glutamate receptors. Activation of transient receptor potential vanilloid 4 (TRPV4) is reported to inhibit hippocampal A-type γ-aminobutyric acid receptor, a ligand-gated chloride ion channel. GlyRs are also ligand-gated chloride ion channels and this paper aimed to explore whether activation of TRPV4 could modulate GlyRs. Methods: Whole-cell patch clamp recording was employed to record glycine-activated current (IGly) and Western blot was conducted to assess GlyRs subunits protein expression. Results: Application of TRPV4 agonist (GSK1016790A or 5,6-EET) increased IGly in mouse hippocampal CA1 pyramidal neurons. This action was blocked by specific antagonists of TRPV4 (RN-1734 or HC-067047) and GlyR (strychnine), indicating that activation of TRPV4 increases strychnine-sensitive GlyR function in mouse hippocampal pyramidal neurons. GSK1016790A-induced increase in IGly was significantly attenuated by protein kinase C (PKC) (BIM II or D-sphingosine) or calcium/calmodulin-dependent protein kinase II (CaMKII) (KN-62 or KN-93) antagonists but was unaffected by protein kinase A or protein tyrosine kinase antagonists. Finally, hippocampal protein levels of GlyR α1 α2, α3 and β subunits were not changed by treatment with GSK1016790A for 30 min or 1 h, but GlyR α2, α3 and β subunits protein levels increased in mice that were intracerebroventricularly (icv.) injected with GSK1016790A for 5 d. Conclusion: Activation of TRPV4 increases GlyR function and expression, and PKC and CaMKII signaling pathways are involved in TRPV4 activation-induced increase in IGly. This study indicates that GlyRs may be effective targets for TRPV4-induced modulation of hippocampal inhibitory neurotransmission.

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Effect of transient receptor potential vanilloid 4 activation on the delayed rectifier potassium current in the hippocampal pyramidal neurons and Kv subunit expression in the hippocampi of mice

10.21203/rs.3.rs-24895/v1 ◽

2020 ◽

Author(s):

Li Zhou ◽

Weixing Xu ◽

Dong An ◽

Chen Men ◽

Yingchun Li ◽

...

Keyword(s):

Transient Receptor Potential ◽

Neuronal Excitability ◽

Pyramidal Neurons ◽

Receptor Potential ◽

Delayed Rectifier ◽

Transient Receptor Potential Vanilloid ◽

Hippocampal Pyramidal Neurons ◽

Protein Levels ◽

Voltage Dependent ◽

Transient Receptor

Abstract Activation of transient receptor potential vanilloid 4 (TRPV4) can increase hippocampal neuronal excitability. Recent studies have reported that TRPV4 may be involved in the pathogenesis of epilepsy. Voltage-gated potassium channels (VGPCs) play an important role in regulating neuronal excitability and abnormal VGPCs expression or function is related to epilepsy. Activation of TRPV4 can modulate ion channels, but whether activation of it could modulate VGPCs in hippocampal neurons remains unknown. Here we examined the effect of TRPV4 activation on the delayed rectifier potassium current (IK) in the hippocampal pyramidal neurons and on the Kv subunits expression. We also explored the role of TRPV4 in changes in Kv subunits expression in mice following pilocarpine-induced status epilepticus (PISE). Application of TRPV4 agonists, GSK1016790A and 5,6-EET, markedly reduced IK in the hippocampal pyramidal neurons, shifted the voltage-dependent inactivation curve to the hyperpolarization direction, and had no effect on the voltage-dependent activation curve. GSK1016790A- and 5,6-EET-induced inhibition of IK was blocked by TRPV4 specific antagonists, HC-067047 and RN1734. GSK1016790A-induced inhibition of IK was markedly attenuated by calcium/calmodulin-dependent kinase II (CaMKII) antagonist, but was not affected by protein kinase C or protein kinase A antagonists. Application of GSK1016790A for up to 1 h did not change the hippocampal protein levels of Kv1.1, Kv1.2, or Kv2.1. Intracerebroventricular injection of GSK1016790A for 3 d reduced the hippocampal protein levels of Kv1.2 and Kv2.1, leaving that of Kv1.1 unchanged. Kv1.2 and Kv2.1 protein levels were reduced markedly in hippocampi on day 3 post PISE, which was significantly reversed by HC-067047. We conclude that activation of TRPV4 inhibits IK in the hippocampal pyramidal neurons, possibly by activating CaMKII. Persistent activation of TRPV4 decreased Kv1.2 and Kv2.1 expression, which may be associated with the decrease in Kv1.2 and Kv2.1 expression following PISE.

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