Insulin and serum increase the number of receptors for vasopressin in a kidney-derived line of cells grown in a defined medium.

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Abstract
A continuous strain of epithelial cells (LLC-PK1L) derived initially from pig kidney grows in a defined medium without serum or hormones. The epithelia from domes, a manifestation of transepithelial transport. The parent cell line, LLC-PK1, forms similar eithelia and has vasopressin-sensitive adenylate cyclase. In this study the binding of 3H-labeled [Lys8]vasopressin was used to examine the vasopressin receptors of LLC-PK1L cells. In the absence of serum, LLC-PK1L cells have receptors with a Kd (10 nM) for 3H-labeled [Lys8]vasopressin similar to that of the parent cell line and of membranes prepared from pig renal medulla, LLC-PK1L cells, however, have only 5% as many receptors as LLC-PK1 cells. The number of receptors and the vasopressin-sensitive adenylate cyclase activity are increased by growing LLC-PK1L cells in medium with 10% fetal bovine serum or with 10 microgram of insulin per ml. The combination of serum plus insulin has a greater effect than either alone. Serum and insulin do not change the apparent affinity of the receptors for vasopressin or the coupling between receptors and adenylate cyclase. Basal and NaF-stimulated adenylate cyclase activity are not affected. Several agents reported to induce receptors for hormones in other tissues have no effect on vasopressin receptors in LLC-PK1L cells.