Na(+) /Ca(2+) exchanger-heterozygote knockout mice display increased relaxation in gastric fundus and accelerated gastric transit in vivo.

BACKGROUND: For the contraction and relaxation of gastric smooth muscles to occur, the intracellular Ca(2+) concentration must be increased and decreased, respectively. The Na(+) /Ca(2+) exchanger (NCX) is a plasma membrane transporter that is involved in regulating intracellular Ca(2+) concentrations. METHODS: To determine the role of NCX in gastrointestinal tissues, we examined electric field stimulation (EFS)-induced relaxations in the circular muscles of the gastric fundus in NCX1 and NCX2 heterozygote knockout mice (HET). KEY RESULTS: The myenteric plexus layers and the longitudinal and circular muscle layers in the gastric fundus of wild-type mice (WT) were strongly immunoreactive to NCX1 and NCX2. EFS induced a transient relaxation that was apparent during the stimulus and a sustained relaxation that persisted after the end of the stimulus. The amplitudes of EFS-induced transient relaxation and sustained relaxation were greater in NCX1 HET and NCX2 HET than in WT. When an inhibitor of nitric oxide synthase was added following the EFS, neither NCX1 HET nor NCX2 HET exhibited transient relaxation, similar to WT. Furthermore, when a PACAP antagonist was added following the EFS, sustained relaxation in NCX1 HET and NCX2 HET was not observed, similar to WT. Next, we examined the effect of NCX heterozygous deficiency on relaxation in response to NO and PACAP in smooth muscles. The magnitude of NOR-1- and PACAP-induced relaxations in NCX1 HET and NCX2 HET was similar to that of WT. CONCLUSIONS & INFERENCES: In this study, we demonstrate that NCX1 and NCX2 expressed in neurons regulate the motility in the gastric fundus.

Na(+) /Ca(2+) exchanger 2-heterozygote knockout mice display decreased acetylcholine release and altered colonic motility in vivo.

BACKGROUND: The Na(+) /Ca(2+) exchanger (NCX) is a plasma membrane transporter involved in regulating intracellular Ca(2+) concentrations. NCX is critical for Ca(2+) regulation in cardiac muscle, vascular smooth muscle, and nerve fibers. However, little is known about the physiological role of NCX in the myenteric neurons and smooth muscles of the gastrointestinal tract. METHODS: To determine the role of NCX1 and NCX2 in gastrointestinal tissues, we examined electric field stimulation (EFS)-induced responses in the longitudinal smooth muscle of the distal colon in NCX1- and NCX2-heterozygote knockout mice. KEY RESULTS: We found that the amplitudes of EFS-induced relaxation that persisted during EFS were greater in NCX2 heterozygous mice (HET) than in wild-type mice (WT). Under the nonadrenergic, noncholinergic (NANC) condition, EFS-induced relaxation in NCX2 HET was similar in amplitude to that of WT. In addition, an NCX inhibitor, YM-244769 enhanced EFS-induced relaxation but did not affect EFS-induced relaxation under the NANC condition, as in NCX2 HET. Unlike NCX2 HET, NCX1 HET displayed no marked changes in colonic motility. These results indicate that cholinergic function in the colon is altered in NCX2 HET. The magnitude of acetylcholine (ACh)-induced contraction in NCX2 HET was similar to that in WT. In contrast, EFS-induced ACh release was reduced in NCX2 HET compared with that in WT. CONCLUSIONS & INFERENCES: In this study, we demonstrate that NCX2 regulates colonic motility by altering ACh release onto the myenteric neurons of the distal colon.

The role of muscarinic receptor subtypes in acetylcholine release from urinary bladder obtained from muscarinic receptor knockout mouse.

We investigated the subtype of prejunctional muscarinic receptors associated with inhibition of acetylcholine (ACh) released from the mouse bladder. We measured endogenous ACh release in the bladder obtained from the wild-type mice and muscarinic 1-5 (M1-M5) receptor knockout (KO) mice. Electrical field stimulation increased ACh release in all bladder preparations obtained from wild-type and M1-M5 receptor KO mice. The amount of ACh released from M1-M3 and M5 receptor KO mice was equal to that in the wild-type mice. In contrast, the amount of electrical field stimulation-induced ACh release in M4 receptor KO mice was significantly larger than that in the wild-type mice, but the extent of increase was small. Atropine increased electrical field stimulation-induced ACh release to levels found in wild-type mice in all M1-M5 receptor KO mice. In M2/M4 receptor double KO mice, the amount of electrical field stimulation-induced ACh release was equivalent to that in the M4 receptor KO mice. The cholinergic component of electrical field stimulation-induced contraction (in the presence of alpha,beta-methylene ATP) in the detrusor of M4 receptor KO mice was no different from that in the detrusor of wild-type mice. M4 receptor immunoreactivity was located between smooth muscle cells, colocalized with choline acetyltransferase immunoreactivity. These results indicate that the prejunctional inhibitory muscarinic receptors are of the M4 and non-M2 receptor subtypes. The nature of the non-M2 receptors remains unknown.

Involvement of M(2) muscarinic receptors in relaxant response of circular muscle of mouse gastric antrum.

Our previous study showed that atropine significantly inhibited the sustained relaxation induced by electrical field stimulation (EFS) in the circular muscle strips prepared from the mouse antrum, and that pituitary adenylate cyclase activating peptide (PACAP) partially mediated the sustained relaxation. The muscarinic receptor subtype associated with the sustained relaxation was examined in the present study by using each muscarinic receptor subtype of knockout (KO) mice. EFS-induced sustained relaxation in the antrum prepared from M(2) receptor KO mice was significantly less than that of wild-type mice. Atropine failed to inhibit this relaxation. On the other hand, similar sustained relaxation and inhibitory effects of atropine to those of wild-type mice were observed in M(1), M(3) and M(4) receptor KO mice. Exogenously added PACAP-27 relaxed the antral strips of wild-type and M(2) receptor KO mice to a similar extent. Immunohistochemical study revealed that M(2) receptor immunoreactivity was localized with PACAP-immunoreactivity in enteric neurons within the antrum of wild-type mice. In contrast, atropine did not affect the EFS-induced sustained relaxation in the gastric fundus. These results suggest that M(2) receptors modulate the sustained relaxation, probably through the regulation of PACAP release, in the mouse antrum.