Aldosterone induces rapid signalling events independent of de novo protein synthesis and these effects play a crucial role in the fine-tuning of latent aldosterone-induced genomic responses. Aldosterone (10nM) rapidly activates Protein kinase D1 (PKD1) within 2 minutes, in M1 cortical collecting duct cells (M1-CCD) – this activation occurs via the mineralocorticoid receptor, transactivation of EGFR and the activation of protein kinase Cδ and ε (1, 2). PKD1 is a serine/threonine kinase with multiple functions including the regulation of vesicle fission from the trans golgi network (TGN), and thereby the control of the rate of protein trafficking to the cell surface. Aldosterone controls sodium homeostasis by regulating the epithelial sodium channel (ENaC) on multiple levels. In M1 cells, PKD1 is essential for the efficient aldosterone-mediated apical trafficking of heterologously expressed ENaC-eCFP subunits on a short time-scale (2min) (1) as well as endogenously expressed ENaC after 24h 10nM aldosterone (3). Aldosterone promoted the translocation of PKD1 from cytosol to the TGN in M1 cells after 30 min, as shown by co-localization with a specific marker of the TGN (TGN38), visualized by immunocytochemistry and laser scanning confocal microscopy. Phosphatidylinositol-4-kinase IIIβ (PI4KIIIβ) is a substrate of PKD1 and is localized specifically to the TGN in M1 cells. Aldosterone induced a significant increase in the interaction between PKD1 and PI4KIIIβ as shown by co-immunoprecipitation and Western blotting (n = 6, p< 0.01, Student’s t-test). It was shown previously that PKD1 phosphorylates PI4KIIIβ to promote the fission of vesicles from the TGN. Using a vesicular stomatitis virus glycoprotein (VSVG) protein transport assay as a measure of the rate of vesicle fission, we did not observe a significant increase in the percentage of cells showing VSVG-GFP localization at the plasma membrane, when pre-treated with 10nM aldosterone for 10min (45.12 ± 5.95), 30min (49.00 ± 5.48) or 60min (66.57 ± 2.40) as compared to vehicle-treated controls 10min (33.97 ± 7.91), 30min (41.99 ± 6.52 ), 60min (52.72 ± 9.97), values shown as mean ± SEM. These results indicate that the regulation of ENaC trafficking via the rapid activation of PKD1 is not a consequence of a general upregulation in the rate of TGN vesicle fission, but rather due to a specific regulation of the trafficking of ENaC-containing vesicles, via rapid PKD1-PI4KIIIβ signalling. Aside from the well-known effects of aldosterone on the regulation of sodium and water homeostasis, aldosterone can also produce deleterious structural changes in tissues by inducing hypertrophy and the dysregulation of proliferation and apoptosis, leading to fibrosis and tissue remodelling (4). In M1-CCD cells, 10nM aldosterone induced an increase in proliferation after 48h, an effect that was PKD1-, PKCδ- and ERK1/2-dependent (5). Overall, rapid aldosterone-induced PKD1 signalling events underlie diverse physiological responses; the specificity of signalling being defined by the subcellular localization of PKD1, its proximity to various substrates and as yet unknown scaffolding proteins, as well as the specific kinetics of activation of the kinase.