Tunneling nanotube (TNT)-like structures are intercellular membranous bridges that mediate the transfer of various cellular components including endocytic organelles. To gain further insight into the magnitude and mechanism of organelle transfer, we performed quantitative studies on the exchange of fluorescently labeled endocytic structures between normal rat kidney (NRK) cells. This revealed a linear increase in both the number of cells receiving organelles and the amount of transferred organelles per cell over time. The intercellular transfer of organelles was unidirectional, independent of extracellular diffusion, and sensitive to shearing force. In addition, during a block of endocytosis, a significant amount of transfer sustained. Fluorescence microscopy revealed TNT-like bridges between NRK cells containing F-actin but no microtubules. Depolymerization of F-actin led to the disappearance of TNT and a strong inhibition of organelle exchange. Partial ATP depletion did not affect the number of TNT but strongly reduced organelle transfer. Interestingly, the myosin II specific inhibitor S-(-)-blebbistatin strongly induced both organelle transfer and the number of TNT, while the general myosin inhibitor 2,3-butanedione monoxime induced the number of TNT but significantly inhibited transfer. Taken together, our data indicate a frequent and continuous exchange of endocytic organelles between cells via TNT by an actomyosin-dependent mechanism.

Neuroendocrine secretory granules, the storage organelles for neuropeptides and hormones, are formed at the transGolgi network, stored inside the cell and exocytosed upon stimulation. Previously, we have reported that newly formed secretory granules of PC12 cells are transported in a microtubule-dependent manner from the trans-Golgi network to the F-actin-rich cell cortex, where they undergo short directed movements and exhibit a homogeneous distribution. Here we provide morphological and biochemical evidence that myosin Va is associated with secretory granules. Expression of a dominant-negative tail domain of myosin Va in PC12 cells led to an extensive clustering of secretory granules close to the cell periphery, a loss of their cortical restriction and a strong reduction in their motility in the actin cortex. Based on this data we propose a model that implies a dual transport system for secretory granules: after microtubule-dependent delivery to the cell periphery, secretory granules exhibit a myosin Va-dependent transport leading to their restriction and even dispersal in the F-actin-rich cortex of PC12 cells. Movie available online

The design of a permeable iron wall depends to a great extent on the transformation kinetics of the chlorinated compounds. Therefore these degradation kinetics of TCE and cis-DCE with commercial iron and their dependence on the properties of the compounds and on the experimental conditions were studied in mixed-batch and column experiments. Since our data cannot sufficiently be described by a pseudo-first-order kinetics, we successfully applied an enhanced model accounting for both zero- and first-order kinetics. The fitted kinetic parameters, however, were found to depend on the experimental conditions and compound properties, which is interpreted in terms of different rate-limiting processes. The zero-order rate constant turned out to be twice as high for cis-DCE as for TCE in both experimental systems. Despite its slower transformation without transport control, the first-order rate constant was about 4 times higher for TCE than for cis-DCE in the mixed-batch vials. We attribute this to the lower water solubility and thus higher sorptivity of TCE at the polished iron surface. In the column experiments, transformation without transport control was twice as fast as in the batch experiments for both compounds. cis-DCE was degraded faster than TCE in the zero- and first-order region. At higher influent concentrations, the zero- and first-order rate constant of TCE decreased, which we assume to be due to the buildup of iron oxides, and transport to the reactive sites was found to depend a little on flow velocity. Due to the slow first-order kinetics of both compounds, we assume diffusion within micropores to be rate-limiting in flow-through systems. These variations in the kinetic parameters of the combined zero- and first-order model suggest that transport and sorption to reactive sites contribute to kinetic control of the degradation of chlorinated ethenes in addition to charge-transfer processes.

This study evaluates the potential of using granular iron metal for the abiotic removal of the organic ground water pollutant trichloroethene (TCE) in the presence of the common inorganic co‐contaminants chromate and nitrate, respectively. Our long‐term column experiments indicate a competitive process between TCE dechlorination and reductive transformation of chromate and nitrate, which is reflected in a significantly delayed onset of TCE dechlorination. Delay times and therefore the ranges of the nonreactive flowpaths increased with increasing experimental duration, resulting in a migration of the contaminants through the iron metal treatment zone. The present investigation also indicates that the calculated migration rates of TCE and the added cocontaminants chromate and nitrate are linearly related to the initial content of the cocontaminants. With an average pore water velocity of 0.6 m/d and a surface area concentration of 0.55 m2/mL in the column, the calculated migration rates varled between 0.10 cm/d and 5.86 cm/d. The particular similarity between the values of TCE migration and the migration of the strong oxidants chromate and nitrate and the long‐term steady state of the TCE dechlorination in the absence of the chromate and nitrate indicates that these competitive transformations are the driving force for the gradual passivation of the granular iron due to the buildup of an electrically insulating Fe(III)‐oxyhydroxide. Based on these passivation processes, general formulae were developed that allow a simplified approximation of breakthrough times for the contaminants TCE, chromate, and nitrate.

† Both authors contributed equally to this work.The protein kinase D (PKD) family comprises multifunctional serine/threonine-specific protein kinases with three mammalian isoforms: PKD1, PKD2 and PKD3. A prominent PKD function is the regulation of basolateraltargeted transport carrier fission from the trans-Golgi network (TGN). To visualize site-specific PKD activation at this organelle, we designed a molecular reporter consisting of a PKD-specific substrate sequence fused to enhanced green fluorescent protein (EGFP), specifically targeted to the TGN via the p230 GRIP domain. Quantitative analyses using a phosphospecific antibody and ratiometric fluorescence imaging revealed that Golgi-specific phosphorylation of the reporter was strictly dependent on stimulation of endogenous PKD or transient expression of active PKD constructs. Conversely, PKDspecific pharmacological inhibitors and siRNA-mediated PKD knockdown suppressed reporter phosphorylation. Using this reporter we investigated a potential role for PKD in the regulation of Golgi complex morphology. Interestingly, nocodazole-induced Golgi complex break-up and dispersal was associated with local PKD activation as measured by reporter phosphorylation and this was efficiently blocked by expression of a dominantnegative PKD mutant or PKD depletion. Our data thus identify a novel link between PKD activity and the microtubule cytoskeleton, whereby Golgi complex integrity is regulated.