Palytoxin stimulated a cation-dependent short-circuit cur-rent (Isc) in rat distal and proximal colon in a concen-tration-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-sen-sitive H + /K + -ATPase into an electrogenic cation trans-porter.