SB-202190

Investigate the potential role of histamine and its receptors on the functional expression of the sodium/hydrogen (Na+/H+) exchanger (NHE)3.

The human epithelial kidney (HK-2) cells were used as an in vitro model of the renal proximal tubule.

HK-2 cells were exposed to histamine 0–1000 nM alone or in combination with chlorphenamine (10 μM) and JNJ-7777120 (1 μM) for 0–48 h. MAPK involvement was determined using the selective inhibitors SB202190 (p38 MAPK), PD98059 (ERK1/2), and SP600125 (SAPK/JNK).

Gene and protein expression were evaluated by qPCR and immunoblotting. The activity of NHE3 was measured by the BCECF-AM-based method.

Histamine (100 nM) induced a concentration-dependent NHE3 gene transcription with a peak 16 h after the treatment, followed by protein translation at 48 h after. A Consistent increase in NHE3 activity was observed at 48 h, but also at 60 min, when both p38 MAPK and ERK1/2 were phosphorylated. JNJ-7777120 blunted the activation and expression of NHE3. Chlorpheniramine was effective only on NHE3 activity.

Histamine shows early (within 60 min) and late (48 h) effects on NHE3 expression. The histamine H1 and H4 receptors are shown to contribute to these effects differentially. The findings of this study extends the evidence for a direct contribution of histamine on the renal reabsorptive machinery.

The epidermal growth factor receptor (EGFR) is located in primary sensory neurons and has been implicated in pain processing. However, its mechanism is still not well understood. The aim of the investigation is to determine whether EGFR signaling affects pain-associated ion channels in nociceptive dorsal root ganglion (DRG) neurons. Herein, we reported that the electrophysiological activity of acid-sensing ion channels (ASICs) was enhanced by epidermal growth factor (EGF) in rat DRG neurons. The application of EGF for 5 min concentration-dependently increased acid-evoked ASIC currents. EGF enhanced the ASIC's maximum responses to acidic stimuli without altering its sensitivity. EGFR did appear to be involved in the EGF-mediated potentiation of ASIC currents, since the potentiation was blocked by the EGFR kinase inhibitor AG556. The EGF-mediated potentiation was ERK-dependent, since the potentiation was prevented by the ERK inhibitor U0126. In contrast, the JNK inhibitor SP600125 and the p38 inhibitor SB202190 had no effect on the EGF-mediated potentiation. Moreover, EGF increased the number of acid-evoked action potentials. Finally, injection of EGF into rat paws exacerbated acid-induced nociceptive behavior in dose-dependent manner. The present results that enhanced functional activity of ASICs by EGF/EGFR signaling provided evidence that EGF/EGFR signaling is a promising target for the treatment of pain caused by tissue acidification.