Action of palytoxin on apical H+/K+-ATPase in rat colon

Palytoxin stimulated a cation-dependent short-circuit current (Isc) in rat distal and proximal colon in a concentration-dependent fashion when applied to the mucosal surface of the tissue. The distal colon exhibited a higher sensitivity to the toxin. The palytoxin-induced Isc was blocked by vanadate but was resistant to ouabain or scilliroside, suggesting the conversion of a vanadate-sensitive H+ /K+-ATPase into an electrogenic cation transporter. Cation substitution experiments with basolaterally depolarized tissues suggested an apparent permeability of the palytoxin-induced conductance of Na+ K+ > Li+. Immunohistochemical control experiments confirmed the absence of the Na+ /K+-ATPase in the apical membrane. Consequently, the pore-forming action of palytoxin is not restricted to Na+ /K+-ATPase but is also observed with the colonic H+ /K+-ATPase.