Summary
To investigate a possible action of insulin on the rat kidney papilla, the binding
of 125I-insulin to papilla microsomes was examined. This binding was specific to insulin
in that it was displaced by increasing concentrations of unlabelled porcine insulin
and to a lesser extent by porcine proinsulin and IGF-I, but not by IGF-II and bGH.
Scatchard plot of the binding data was curvilinear consistent with either two classes
of receptors with different affinities or a single class of receptors that showed
negative cooperativity. A small fraction of 125I-insulin (maximum 2%) was degraded during incubation, but with a Km two order of
magnitude higher than the constant of affinity for binding. Insulin stimulates the
incorporation of phosphate to phosphatidylcholine in a dose-dependent manner, reaching
a maximum with 10 nM insulin. This data showed both the presence of specific insulin
receptors in the kidney papilla and an insulin action through the synthesis of phospholipids
by insulin.
Key words
Insulin - Receptor - Renal Papilla - Phospholipids
