Under hypotonic conditions, the regulatory volume decrease (RVD) is essential to maintain physiological homeostasis and functions in diverse biological systems. Intracellular Ca2+ has been reported as an important mediator of this response, but the underlying Ca2+ mechanism responsible for RVD is still controversial. Here we investigate the role of Ca2+ in the RVD response using live-cell imaging, microspectrofluorimetry, and a patch-clamp technique. A typical RVD was observed in submandibular gland acinar cells after swelling in a hypotonic solution, whereas intracellular Ca2+ chelation completely inhibited the RVD response. The incidence and magnitude of the Ca2+ transient were proportional to the degree of hypotonicity of the extracellular medium, and there was a close relationship between intracellular Ca2+ concentration and the volumetric changes of the cells. Notably, this response was mediated by Ca2+-induced Ca2+ release, which is triggered by Ca2+ influx via stretch-activated TRPM7 channels. Furthermore, we detected the generation of Cl- currents in the swelling acinar cells upon hypotonic stress, and the current profile matched that of the Ca2+-activated Cl- currents. A specific inhibitor of Cl- currents also inhibited the RVD response. In conclusion, an intracellular Ca2+ increase in response to osmotically induced cell swelling plays a critical role in RVD in salivary gland acinar cells.
Keywords: cell biology; cell signaling; mechanotransduction; molecular biology; physiology; signal transduction.