Emerging Concepts in Ion Channel Biophysics

Emerging Concepts in Ion Channel Biophysics

Poster Abstracts

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.

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