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Emerging Concepts in Ion Channel Biophysics
Poster Abstracts
81
47-POS
Board 47
Functional Coupling between NHE1 Exchanger and TRPA1 Channel in Nociceptive
Neurons.
Vladimir A. Martinez Rojas
1
, Norma L. Gomez Viquez
1
, Francisco Mercado
2
, Janet
Murbartian
1
.
1
Cinvestav, Mexico, Tlalpan, Mexico,
2
Instituto Nacional de Psiquiatria Ramon de la Fuente
Muñiz, Mexico, Tlalpna, Mexico.
The regulation of the intracellular pH (pHi) in neurons is an elemental physiological process.
Changes in pHi affect the functions of enzymes, ion channels, and other macromolecules, thus
affecting synaptic transmission and neuronal excitability. It has been reported that inhibition of
the Na+/H+ (NHE1) exchanger increases discharge activity in nociceptors and intensify
formalin-induced acute and chronic nociceptive behaviors. Besides, TRPA1 receptor is activated
by diverse stimulus, among then, alkaline or acid pHi. Since these proteins are expressed in
primary afferent nociceptive neurons, TRPA1 channel activity could be closely modulated by
NHE1 and contributes to modulate the nociceptive transmission. To test this possibility, we
evaluated the responses of NHE1 and TRPA1 with patch clamp recording and microfluorometry
in native adult rat dorsal root ganglion (DRG) dissociated neurons.
We first examined changes of the cytosolic pH in BCECF-loaded neurons upon inhibition of
NHE1 exchanger with zoniporide. The application of zoniporide (10, 30 and 100 µM) in the
small-diameter DRG neurons dissociated, increases the intracellular concentration of protons in
dose-dependent manner. In whole-cell patch clamp recording, we found that application of
zoniporide no evoke any change on membrane currents in DRG neurons. Therefore, we evocated
TRPA1 current through use of 300 µM AITC (specific agonist) and determinate the effect of the
inhibition of NHE1 by zoniporide on AITC–induced current. The inward current induced by
AITC in DRG neurons underwent a desensitization giving a smaller response on repeated
applications. Nevertheless, the grade of desensitization is decreased with the application of
zoniporide (30 µM). We conclude that NHE1 and TRPA1 are sensors for intracellular
acidification in DRGs and suggest that it functions within the pain pathway to mediate sensitivity
to intracellular acidosis.