Modulation of transient receptor potential Vanilloid 4-mediated membrane currents and synaptic transmission by protein kinase C.
BACKGROUND
Transient receptor potential Vanilloid (TRPV) receptors are involved in nociception and are expressed predominantly in sensory neurons. TRPV1, a non-selective cation channel has been extensively studied and is responsible for inflammatory thermal hypersensitivity. In this study, the expression and function of TRPV4 have been characterized and compared with those of TRPV1.


RESULTS
Immunohistochemical studies revealed that both TRPV1 and TRPV4 were co-expressed in dorsal root ganglion (DRG) neuronal cell bodies and in the central terminals of laminae I and II of the spinal dorsal horn (DH). In Ca2+ fluorescence imaging and whole-cell patch-clamp experiments, TRPV1- and TRPV4-mediated responses were observed in a population of the same DRG neurons. Sensitization of TRPV1 has been shown to be involved in inflammatory pain conditions. Incubation with phorbol 12, 13-dibutyrate (PDBu), a PKC activator, resulted in a significant potentiation of TRPV4 currents in DRG neurons. In TRPV4 expressing HEK 293T cells, PDBu increased 4alpha-phorbol 12, 13-didecanoate (4alpha-PDD)-induced single-channel activity in cell-attached patches, which was abrogated by bisindolylmaleimide (BIM), a selective PKC inhibitor. TRPV4 is also expressed at the central terminals of sensory neurons. Activation of TRPV4 by 4alpha-PDD increased the frequency of miniature excitatory post synaptic currents (mEPSCs) in DRG-DH neuronal co-cultures. 4alpha-PDD-induced increase in the frequency of mEPSCs was further enhanced by PDBu. The expression of TRP channels has been shown in other areas of the CNS; application of 4alpha-PDD significantly increased the mEPSC frequency in cultured hippocampal neurons, which was further potentiated by PDBu, whereas, TRPV1 agonist capsaicin did not modulate synaptic transmission.


CONCLUSIONS
These results indicate that TRPV4 and TRPV1 are co-expressed in certain DRG neurons and TRPV4 can be sensitized by PKC not only in DRG neuronal cell bodies, but also in the central sensory and non-sensory nerve terminals. Co-expression of TRPV1 and TRPV4 ion channels, their modulation of synaptic transmission and their sensitization by PKC may synergistically play a role in nociception.
Cao
De-Shou
DS
Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, IL 62702, USA. dcao2@siumed.edu
Yu
Shuang-Quan
SQ
Premkumar
Louis S
LS
D000818:Animals; D002460:Cell Line; D004594:Electrophysiology; D005727:Ganglia, Spinal / Q000166:cytology; D006801:Humans; D055369:Miniature Postsynaptic Potentials; D010146:Pain / Q000503:physiopathology; D011493:Protein Kinase C / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011984:Sensory Receptor Cells / Q000502:physiology; D009435:Synaptic Transmission; D050916:TRPV Cation Channels / Q000032:analysis / Q000502:physiology*
D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; C486577:Trpv4 protein, rat; D011493:Protein Kinase C