TRPV4 Complexes With the Na/Ca Exchanger and IP Receptor 1 to Regulate Local Intracellular Calcium and Tracheal Tension in Mice.

Intracellular Ca is critical for regulating airway smooth muscle (ASM) tension. A rapid rise in the intracellular Ca concentration ([Ca]) of ASM cells is crucial for modulating the intensity and length of the ASM contraction. Because this rapid increase in [Ca] largely depends on the balance between Ca released from intracellular Ca stores and extracellular Ca entry, exploring the mechanisms mediating Ca transport is critical for understanding ASM contractility and the pathogenesis of bronchial contraction disorders. Transient receptor potential vanilloid 4 (TRPV4) is a highly Ca-permeable non-selective cation channel that mediates Ca influx to increase [Ca], which then directly or indirectly regulates the contraction and relaxation of ASM. The [Ca] returns to basal levels through several uptake and extrusion pumps, such as the sarco(endo)plasmic reticulum Ca ATPase and inositol 1,4,5-trisphosphate receptors (IPRs), the plasmalemmal Ca ATPase, and the plasma membrane Na/Ca exchanger (NCX). Thus, to further understand ASM tension regulation in normal and diseased tissue, the present study examined whether an interaction exists among TRPV4, IPRs, and NCX. The TRPV4-specific and potent agonist GSK1016790A increased [Ca] in mouse ASM cells, an effect that was completely blocked by the TRPV4-specific antagonist HC067047. However, GSK1016790A induced relaxation in mouse tracheal rings precontracted with carbachol . To determine the mechanism underlying this TRPV4-induced relaxation of ASM, we blocked specific downstream molecules. We found that the GSK1016790A-induced relaxation was abolished by the NCX inhibitors KB-R7943 and LiCl but not by specific inhibitors of the Ca-activated large-, intermediate-, or small-conductance K channels (BK, IK, and SK, respectively). The results of co-immunoprecipitation (co-IP) assays showed an interaction of TRPV4 and IPR with NCX. Taken together, these findings support a physical and functional interaction of TRPV4 and IPR with NCXs as a novel TRPV4-mediated Ca signaling mechanism and suggest a potential target for regulation of ASM tension and treatment of respiratory diseases, especially tracheal spasm.