Overexpression of Na+/Ca2+ exchanger 1 display enhanced relaxation in the gastric fundus.

In gastric smooth muscles, the released Ca2+ activates the contractile proteins and Ca2+ taken up from the cytosol cause relaxation. The Na+/Ca2+ exchanger (NCX) is an antiporter membrane protein that controls Ca2+ influx and efflux across the membrane. However, the possible relation of NCX in gastric fundus motility is largely unknown. Here, we investigated electric field stimulation (EFS)-induced relaxations in the circular muscles of the gastric fundus in smooth muscle-specific NCX1 transgenic mice (Tg). EFS caused a bi-phasic response, transient and sustained relaxation. The sustained relaxation prolonged for an extended period after the end of the stimulus. EFS-induced transient relaxation and sustained relaxation were greater in Tg than in wild-type mice (WT). Disruption of nitric oxide component by N-nitro-l-arginine, EFS-induced transient and sustained relaxations caused still marked in Tg compared to WT. Inhibition of PACAP by antagonist, EFS-induced sustained relaxation in Tg was not seen, similar to WT. Nevertheless, transient relaxation remained more pronounced in Tg than in WT. Next, we examined responses to NO and PACAP in smooth muscles. The magnitudes of NOR-1, which generates NO, and PACAP-induced relaxations were greater in Tg than in WT. In this study, we demonstrate that NCX1 regulates gastric fundus motility.

Roles of Na(+)/Ca(2+) exchanger isoforms NCX1 and NCX2 in motility in mouse ileum.

The Na(+)/Ca(2+) exchanger (NCX) is a plasma membrane transporter that is involved in regulating intracellular Ca(2+) concentrations in various tissues. The physiological roles by which NCX influences gastrointestinal motility are incompletely understood, although its role in the heart, brain, and kidney has been widely investigated. In this study, we focused on the functions of the NCX isoforms, NCX1 and NCX2, in the motility of the ileum in the gastrointestinal tract. We investigated the response to electric field stimulation (EFS) in the longitudinal smooth muscle of the ileum obtained from wild-type mice (WT), NCX1-heterozygote knockout mice (NCX1 HET), NCX2 HET and smooth muscle-specific NCX1.3 transgenic mice (NCX1.3 Tg). EFS induced a phasic contraction that persisted during EFS and a tonic contraction that occurred after the end of EFS. We found that the amplitudes of the phasic and tonic contractions were significantly smaller in NCX2 HET, but not in NCX1 HET, compared to WT. Moreover, the magnitudes of acetylcholine (ACh)- and substance P (SP)-induced contractions of NCX2 HET, but not of NCX1 HET, were smaller compared to WT. In contrast, the amplitudes of the phasic and tonic contractions were greater in NCX1.3 Tg compared to WT. Similar to EFS, the magnitude of ACh-induced contraction was greater in NCX1.3 Tg than in WT. Taken together, our findings indicated that NCX1 and NCX2 play important roles in ileal motility and suggest that NCX1 and NCX2 regulate the motility in the ileum by controlling the sensitivity of smooth muscles to ACh and SP.

Na/Ca(2+) exchanger 1 transgenic mice display increased relaxation in the distal colon.

Na(+)/Ca(2+) exchanger 1 (NCX1) is a plasma membrane transporter involved in regulating intracellular Ca(2+) concentrations. NCX1 is critical for Ca(2+) regulation in cardiac muscle, vascular smooth muscle and nerve fibers. However, little is known about the physiological role of NCX1 in gastrointestinal motility. To determine the role of NCX1 in gastrointestinal tissues, we examined electric field stimulation (EFS)-induced responses in the longitudinal smooth muscle of the distal colon in smooth muscle-specific NCX1 transgenic mice (Tg). Tg show that NCX1 protein was overexpressed in the distal colon at a level twofold greater than that of endogenous NCX1. We found that the amplitudes of EFS-induced relaxation that persisted during EFS were greater in Tg than in wild-type mice (WT). Under the nonadrenergic, noncholinergic condition, the EFS-induced relaxation in Tg was also greater than that in WT. Inhibition of NO synthase, CO synthase, soluble guanylate cyclase (sGC), and protein kinase G (PKG) all attenuated the enhanced relaxation in Tg, demonstrating the importance of NCX1 in NO/sGC/PKG signaling. The action of NOR-1, an NO donor, induced enhanced relaxation in Tg compared with that in WT. Unlike NOR-1, pituitary adenylate cyclase-activating peptide and vasoactive intestinal peptide induced a similar relaxation in Tg compared with that in WT. In this study, we demonstrate that NCX1 plays an important role in smooth muscle motility in the mouse distal colon.

Clofibrate relaxes the longitudinal smooth muscle of the mouse distal colon through calcium-mediated desensitisation of contractile machinery.

Peroxisome proliferator-activated receptor α (PPAR-α) is a ligand-activated transcription factor that exerts strong effects on metabolic pathways. Our aim was to elucidate the effect of clofibrate, a PPAR-α agonist, on the longitudinal muscle of the mouse distal colon. We initially found that clofibrate induced a relaxation response in this muscle. Notably, the PPAR-α antagonists GW9662 and T0070907 did not attenuate this clofibrate-induced relaxation. The structurally related PPAR-α agonists fenofibrate and bezafibrate induced relaxation in the distal colon as effectively as clofibrate. In contrast, wy-14643, which activates PPAR-α more selectively than clofibrate, had no effect. Furthermore, clofibrate-induced relaxation was not affected by N-nitro-L-arginine, an NO synthase inhibitor, 1H-[1,2,4]-oxadiazolo-[4,3- a]quinoxaline-1-one, a soluble guanylate cyclase inhibitor, or H89, a protein kinase A inhibitor. Tetrodotoxin, an Na⁺ channel blocker, and glibenclamide, apamin, charybdotoxin and XE991, various K⁺ channel blockers, had no effect on clofibrate-induced relaxation. Importantly, clofibrate induced a relaxation response that was not accompanied by any alteration in the cytoplasmic Ca²âº concentration in the longitudinal muscle of the mouse distal colon. Moreover, calyculin A, a myosin light-chain phosphatase (MLCP) inhibitor, attenuated clofibrate-induced relaxation. Our findings indicate that clofibrate relaxes the longitudinal smooth muscle of the mouse distal colon by regulating MLCP activity.

PPARα contributes to colonic protection in mice with DSS-induced colitis.

Inflammatory bowel disease (IBD) is characterized by repeated chronic inflammation of the gastrointestinal tract. We have used the complementary model of colonic inflammation to examine the roles of peroxisome proliferator-activated receptor α (PPARα) in colonic inflammation and thus its possible role in IBD. We characterized an innate immune-mediated model of colitis induced by dextran sulfate sodium (DSS). Mice with DSS-induced colitis were injected with Wy-14643 (2 mg/kg) as a PPARα agonist every day from day 0 to day 5. We show that mice given Wy-14643 were less susceptible to experimental acute colitis induced by DSS, and this decreased susceptibility was correlated with decreased production of IFNγ, IL-1ß, IL-6, and TNF-α. Our findings suggest that PPARα has a role in controlling colonic inflammation and mucosal tissue homeostasis.