Binding of ouabain to normal and tumoral pancreatic islet cells

The binding of [3H(G)]ouabain was examined in both rat pancreatic islets and tumoral islet cells (RINm5F line). In the islets, the specific binding was considered too low to allow for extensive investigations, taking into account the limited number of islets readily available. In the RINm5F cells, which bound more ouabain than normal islet cells, the time course for binding, its temperature dependency, its competitive inhibition by K+, the number of binding sites, their affinity, and the turnover of ATP per binding site were all similar to those found in other cell types. An incomplete dissociation of [3H(G)]ouabain by unlabelled glycoside and the stimulation of binding by D-glucose were noticed, both phenomena being possibly attributable, in part at least, to the functional response of the RINm5F cells to D-glucose with resulting activation of exocytosis-endocytosis coupling.