Na+/Ca2+ Exchange and Airway Smooth Muscle Inflammation

Abstract

Airway inflammation leads to increased intracellular Ca2+ ([Ca2+]i) in airway smooth muscle (ASM). There is now growing evidence that the bidrectional plasma membrane Na+/Ca2+ exchange (NCX) may contribute to ASM [Ca2+]i regulation. However, the roles of NCX‐mediated Ca2+ influx vs. efflux, or the role of NCX in airway inflammation are largely unknown. In the present study, we examined NCX expression and function in human ASM exposed to the pro‐inflammatory cytokines TNFα and IL‐13. Western blot analysis of human ASM tissue showed significant expression of the NCX1 isoform, with substantial increase in expression following overnight cytokine exposure. In fura‐2 loaded human ASM cells, NCX‐mediated Ca2+ influx as well as efflux (measured as slopes of changes in [Ca2+]i) was elicited using techniques previously described for cardiac muscle. Contribution of NCX was verified by measuring [Na+]i using the fluorescent Na+ indicator SBFI. NCX‐mediated influx was verified by demonstrating prevention of rising [Ca2+]i or falling [Na+]i in the presence of the NCX inhibitor KBR7943. In second set of studies, NCX siRNA transfection of human ASM substantially blunted efflux and influx mode of NCX (siRNA effect verified by Western blot). Exposure to TNF‐α as well as IL‐13 significantly enhanced influx mode of NCX. Although both cytokines also increased efflux mode of NCX, these effects were relatively smaller. These data suggest that NCX may be one mechanism contributing to inflammation‐induced enhancement of [Ca2+]i.Supported by NIH grants HL74309, RR024150, and the Flight Attendants Medical Research Institute (FAMRI). Additional funding from the Department of Anesthesiology, Mayo Clinic.