The effect of cholera toxin and cholera toxin B subunit on the nasal mucosal membrane

The effects of the self-adjuvanting substances, cholera toxin (CT) and cholera toxin B subunit (CTB), on rabbit nasal mucosal membrane, were investigated by using Ussing chambers. The control nasal mucosa (lateral wall), isolated from rabbits and mounted in the chamber, showed transepithelial potential difference, short-circuit current and conductance of -10 mV, 200 microA cm-2 and 20 mS cm-2, respectively. These parameters were compared with mucosa isolated from human inferior conchae, showing that rabbit nasal mucosa may be usable to understand effects on human mucosa. When the mucosa was exposed to various concentrations of CTB and CT, the short-circuit current and conductance of the mucosa increased with increasing concentration. CTB showed gradual increase in the short-circuit current when added in the same molar concentration as the B subunit contained in CT, which caused drastic changes by increasing the current to infinite value. Furthermore, the total amount of transepithelially fluxed CTB, which occurred rapidly after addition to the mucosal side of the chambers, increased with increasing CTB concentration. On the other hand, less flux was observed after addition of CT. These changes could be blocked by addition of ganglioside GM1. This demonstrates that the effect of CTB on the rabbit mucosal membrane are different from those of CT, although both CT and CTB act specifically on the membrane via the CTB receptor, ganglioside GM1.