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The nasal respiratory mucosa of the rabbit has a leaky epithelium actively transporting polypeptides by a specific transcytosis probably involved in sampling antigens. The transfer displays saturation kinetics and is abolished by metabolic inhibitors, actin filamet and microtubule disassemblers, inhibitors of vesicle fusion, and receptor recycling;it accepts polypeptide-covered but not uncovered nanoparticles.

We have previously demonstrated that polypeptides (elcatonin and ACTH) can be actively absorbed across the rabbit nasal mucosa. In this paper we show that elcatonin is also transported when it is adsorbed onto microspheres (diameter: 0.5 micron). whereas the elcatonin-uncovered microspheres do not display any net transport. Cytochalasin D (0.1 microgram/ml) abolishes the net absorption of elcatonin presented either alone or adsorbed. At the same concentration the inhibitor does not affect cellular active ion transports (and hence metabolism); although it increases intercellular ion and elcatonin permeability, it does not affect intercellular and paracellular permeability of the elcatonin-covered microspheres. Altogether, these results show that polypeptide transport is supported by a specific vesicular transfer inhibited by cytochalasin D by disassembly of the actin cytoskeleton, probably at the apical border of the cell.

An active absorption of polypeptides (elcatonin = CCT; adrenocorticotropic hormone) had been previously observed in the nasal respiratory mucosa of the rabbit. Its saturation kinetics and the parallel absence of a net transfer of other non-polypeptidic organic markers excluded the involvement of a simple pinocytosis. This absorption has been now better localized and further characterized. Unidirectional CCT fluxes (determined with radioimmunoassay) have been concomitantly monitored with transepithelial electric potential difference (Vms). Although the mucosae covering the ectoturbinal A and the lower and upper conchae displayed similar Vms, the active CCT transport was only evidenced in the upper concha. In this region cytochalasin B (which by disassembling actin microfilaments prevents the apical formation of vesicles in epithelial cells) and monensin (which prevents the split of the ligand-receptor complex in the endosomes) both eliminated the net CCT absorption, however, also permanently increasing the passive CCT junctional permeability. Aluminium fluoride (which prevents the fusion of endocytic vesicles into endosomes) and colchicine (which disrupts microtubules along which vesicles move in the cytoplasm) also permanently abolished net CCT transport, without affecting, or shortly and transiently affecting, passive permeability. On the whole these results are in favor of an active CCT transport supported by a specific vesicular transport.