palytoxin and scilliroside

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.

Topics: Acrylamides; Animals; Borates; Bufanolides; Cell Membrane Permeability; Cnidarian Venoms; Colon; Enzyme Inhibitors; H(+)-K(+)-Exchanging ATPase; Intestinal Mucosa; Ion Channels; Ion Transport; Lithium; Membrane Potentials; Ouabain; Potassium; Proton Pumps; Rats; Rats, Wistar; Sodium; Sodium-Potassium-Exchanging ATPase; Vanadates