Na⁺/Ca²⁺Exchanger 1 Transgenic Mice Display Increased Relaxation in the Distal Colon

Na+/Ca2+ exchanger 1 (NCX1) is a plasma membrane transporter involved in regulating intracellular Ca2+ concentrations. NCX1 is critical for Ca2+ 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. i 2014 S.