| Calcium (Ca2+) influx into cells is a highly regulated process because of its broad range of cellular effects. The Transient Receptor Potential or TRP superfamily of generally non-selective, cation permeable ion channels represents a relatively new class of Ca2+ entry channels. Broadly expressed in tissues and conserved within eukaryotes, many TRP family members are involved in sensory signal transduction cascades. Here we report that the brain specific TRP, TRPC5 is contained in vesicles just beneath the plasma membrane previously undetected by conventional imaging techniques. Total internal reflection fluorescence (TIRF) or evanescent field (EF) microscopy reveals that these TRPC5 channel-containing vesicles are highly motile and can be rapidly translocated to the plasma membrane following growth factor stimulation. Biochemistry, electrophysiology, and confocal imaging of fluorescent biosensors confirm that TRPC5 channels are inserted into the plasma membrane and that channel insertion is a phosphoinositide 3-kinase (PI3K)-dependent process. The Rho-GTPase Rac1 and phosphatidylinositol-4-phosphate 5-kinase (PIP5Kalpha) play key roles in mediating TRPC5 incorporation into the membrane. The related channel TRPC1 + TRPC5 is insensitive to Rac1-mediated translocation and is excluded from neuronal growth cones. The process of TRPC5 translocation is conserved in neurons, where its surface expression modulates the extension rates of growing axons. Rapid membrane insertion of Ca 2+-permeable channels to produce localized Ca2+-influx might represent a mechanism by which TRP channels mediate changes in cellular motility or morphology. |
