The role of the cytoskeleton in volume regulation and beading transitions in PC12 neurites

We present investigations on volume regulation and beading shape transitions in PC12 neurites conducted using a flow-chamber technique. By disrupting the cell cytoskeleton with specific drugs we investigate the role of its individual components in the volume regulation response. We find that microtubule disruption increases both swelling rate and maximum volume attained, but does not affect the ability of the neurite to recover its initial volume. In addition, investigation of axonal beading --also known as pearling instability-- provides additional clues on the mechanical state of the neurite. We conclude that the initial swelling phase is mechanically slowed down by microtubules, while the volume recovery is driven by passive diffusion of osmolites. Our experiments provide a framework to investigate the role of cytoskeletal mechanics in volume homeostasis

Relative effects of furosemide and ethacrynic acid on ion transport and energy metabolism in slices of rat kidney-cortex

The effects of furosemide and ethacrynic acid have been studied using slices of rat kidney cortex incubated in a Ringer medium. At concentrations from 0.2–2.0 mM, furosemide had no significant effect on the tissue ATP content or on the metabolism-dependent net movements of intracellular Na + , K + and Ca 2+ . It did, however, induce an increase in the net, outward movement of Cl − ; we suggest that this may have srisen from inhibition of a Cl − accumulating mechanism. In contrast, ethacrynic acid in the same concentration range caused marked reduction of cell respiration and ATP content and virtually total inhibitition of several processes of ion transport (Na + , Cl − and Ca 2+ loss, and K + uptake). Concentrations of furosemide greater than 5 mM caused marked inhibition of energy metabolism and transport of ions, and 10 mM furosemide had quantitatively similar effects to 2 mM ethacrynic acid. Electron micrographs of kidney-cortex slices treated with the diuretics at 2 mM show that the ultrastructure was well maintained in the presence of furosemide but that ethacrynic acid caused severe structural disorganisation and necrosis. The mitochondria were generally in the orthodox configuration in the presence of furosemide, but swollen in ethacrynic acid in accord with the marked effects of 2 mM ethacrynate on mitochondrial energy metabolism. Of the effects we have detected, that of low concentrations of furosemide on Cl − movement appears to be rather specific. Higher concentrations of this agent (5 mM and above), and all concentrations of ethacrynic acid studied (0.1–5.0 mM), have several inhibitory effects which seem to result from primary inhibition of mitochondrial activities and are presumably manifestations of toxicity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46309/1/210_2004_Article_BF00506264.pd

The epithelial cholinergic system of the airways

Acetylcholine (ACh), a classical transmitter of parasympathetic nerve fibres in the airways, is also synthesized by a large number of non-neuronal cells, including airway surface epithelial cells. Strongest expression of cholinergic traits is observed in neuroendocrine and brush cells but other epithelial cell types—ciliated, basal and secretory—are cholinergic as well. There is cell type-specific expression of the molecular pathways of ACh release, including both the vesicular storage and exocytotic release known from neurons, and transmembrane release from the cytosol via organic cation transporters. The subcellular distribution of the ACh release machineries suggests luminal release from ciliated and secretory cells, and basolateral release from neuroendocrine cells. The scenario as known so far strongly suggests a local auto-/paracrine role of epithelial ACh in regulating various aspects on the innate mucosal defence mechanisms, including mucociliary clearance, regulation of macrophage function and modulation of sensory nerve fibre activity. The proliferative effects of ACh gain importance in recently identified ACh receptor disorders conferring susceptibility to lung cancer. The cell type-specific molecular diversity of the epithelial ACh synthesis and release machinery implies that it is differently regulated than neuronal ACh release and can be specifically targeted by appropriate drugs

On the meaning of effects of substrate structure on biological transport

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44802/1/10863_2005_Article_BF01516050.pd