The alkaline pH-activated, two-pore domain K+ channel K2P5.1 (also known as TASK2/KCNK5) plays an important role in maintaining the resting membrane potential, and contributes to the control of Ca2+ signaling in several types of cells. Recent studies highlighted the potential role of the K2P5.1 K+ channel in the pathogenesis of autoimmune diseases such as rheumatoid arthritis and multiple sclerosis. The aim of the present study was to elucidate the pathological significance of the K2P5.1 K+ channel in inflammatory bowel disease (IBD). The degrees of colitis, colonic epithelial damage, and colonic inflammation were quantified in the dextran sulfate sodium-induced mouse IBD model by macroscopic and histological scoring systems. The expression and functional activity of K2P5.1 in splenic CD4+ T cells were measured using real-time PCR, Western blot, and fluorescence imaging assays. A significant increase was observed in the expression of K2P5.1 in the splenic CD4+ T cells of the IBD model. Concomitant with this increase, the hyperpolarization response induced by extracellular alkaline pH was significantly larger in the IBD model with the corresponding intracellular Ca2+ rises. The expression of K2P5.1 was higher in CD4+CD25− T cells than in CD4+CD25+ regulatory T cells. The knockout of K2P5.1 in mice significantly suppressed the disease responses implicated in the IBD model. Alternations in intracellular Ca2+ signaling following the dysregulated expression of K2P5.1 were associated with the disease pathogenesis of IBD. The results of the present study suggest that the K2P5.1 K+ channel in CD4+CD25− T cell subset is a potential therapeutic target and biomarker for IBD.

Angiotensin II (Ang II) infusion into rats elevates local angiotensin II levels through an AT1 receptor–dependent pathway in the kidney. We examined whether treatment with an angio-tensin-converting enzyme (ACE) inhibitor, temocapril, or an AT1-receptor blocker, olmesartan, prevented elevation of Ang II levels in the kidney of angiotensin I (Ang I)-infused rats. Rats were infused with Ang I (100 ng/min) and treated with temocapril (30 mg/kg per day, n = 10) or olmesartan (10 mg/kg per day, n = 9) for 4 weeks. Ang I infusion significantly elevated blood pressure compared with vehicle-infused rats (n = 6). Treatment with temocapril or olmesartan suppressed Ang I–induced hypertension. Temocapril suppressed both plasma and renal ACE activity. Ang I infusion increased Ang II content in the kidney. Interestingly, temocapril failed to reduce the level of Ang II in the kidney, while olmesartan markedly suppressed an increase in renal Ang II levels. These results suggest a limitation of temocapril and a benefit of olmesartan to inhibit the renal renin–angiotensin system and suggest the possible existence of an ACE inhibitor–insensitive pathway that increases Ang II levels in rat kidney.