Short-term effect on intestinal epithelial Na+/H+ exchanger by Giα1,2-coupled 5-HT1A and Gq/11-coupled 5-HT2 receptors

The present study evaluated the effect of 5-hydroxytryptamine (5-HT) on intestinal Na+/H+ exchanger (NHE) activity and the cellular signaling pathways involved in T84 cells. T84 cells express endogenous NHE1 and NHE2 proteins, detected by immunoblotting, but not NHE3. The rank order for inhibition of NHE activity in acid-loaded T84 cells was 5-(N-ethyl-N-isopropyl)-amiloride (EIPA; IC50 = 519 [465, 579] nM) > cariporide (IC50 = 630 [484, 819] nM) > amiloride (IC50 = 19 [16, 24] μM); the NHE3 inhibitor S3226 was found to be devoid of effect. This different inhibitory sensitivity indicates that both NHE1 and NHE2 isoforms may play an active role in Na+-dependent intracellular pH (pHi) recovery in T84 cells. Short-term exposure (0.5 h) of T84 cells to 5-HT increased NHE activity in a concentration-dependent manner. The stimulation induced by 5-HT (30 μM) was partially inhibited by both WAY 100135 (300 nM) and ketanserin (300 nM), antagonists of 5-HT1A and 5-HT2 receptors, respectively. NHE activity was significantly increased by 8-OH-DPAT and α-methyl-5-HT, agonists of, respectively, 5-HT1A and 5-HT2 receptors. An incubation of T84 cells with anti-Gs and anti-Gβ antibodies complexed with lipofectin did not prevent the 5-HT-induced stimulation of NHE activity. Overnight treatment with anti-Giα1,2 and anti-Gq/11 antibodies complexed with lipofectin blocked the stimulatory effect induced by 8-OH-DPAT and α-methyl-5-HT, respectively. It is concluded that in T84 cells 5-HT enhances intestinal NHE activity through stimulation of Giα1,2-coupled 5-HT1A and Gq/11-coupled 5-HT2 receptors.