Common recycling compartment

The endocytotic recycling pathways of polarized epithelial cells (Fig. 8.5), such as en-terocytes, are generally more complex than those in nonpolarized cells. In these entero-cytes there is a common recycling compartment (CRC) that receives molecules from both apical and basolateral membranes and is able to correctly return them to the appropriate membrane or membrane recycling compartment (ARC or BLRC) (25). The signals required for this sorting step have not been defined as of yet, but are presumably similar to... 

After internahsation into isolated rat type II pneumocytes, SP-A and Hpid were taken up via the coated-pit pathway and resided in a common compartment, positive for the early endosomal marker EEAl but negative for the lamellar body marker 3C9 (WissEL et al. 2001). SP-A then recycled rapidly to the cell surface via Rab4-associated recycHng vesicles. Internalised lipid was transported toward a Rab7-, CD63-, 3C9-positive compartment, i.e., lamellar bodies. Inhibition of calmodulin led to inhibition of uptake and transport out of the EEAl-positive endosome and thus of resecretion of both components. Inhibition of intravesicular acidification (bafilomycin Ai) led to decreased uptake of both surfactant components. It inhibited transport out of early endosomes for lipid only, not for SP-A. 

For each mole of hydrogen consumed in the anode compartment, one mole of carbon dioxide and one mole of water are produced. Hydrogen is made available to the anode in a carbonate fuel cell by extracting it from a common fuel (such as by steam-reforming natural gas). The fuel cell reactions use both H2 and CO in the anode. The commonly available carbonaceous fuels need to be converted to a usable form, either inside or outside the cell (further discussed in Section 2.3). Oxygen is supplied from air, and carbon dioxide is made available by recycling it from the anode exhaust. For this purpose, the anode exhaust is oxidized with the feed air in an oxidizer prior to its introduction into the cathode. Details on carbonate fuel cell chemistry are avilable in the Fuel Cell Handbook (Fuel Cell Handbook 2002). 

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