WRK1 cells: a model system for studying properties of V1a vasopressin receptors

WRK1 cells, an established cell line derived from a chemically induced mammary tumor in the rat, are sensitive to vasopressin. Binding studies with intact WRK1 cells indicated the presence of a single population of [3H]vasopressin binding sites (dissociation constant, Kd = 12.7 +/- 0.2 nM, maximal binding capacity = 75 +/- 6 fmole/10(6) cells). Competition experiments using a series of vasopressin analogs with enhanced selectivity for the three subtypes of receptors already characterized--that is, renal V2 receptors, V1 receptors of the vascular or hepatic subtype (V1a), and V1 receptors from rat adenohypophysis (V1b)--indicated that vasopressin receptors from WRK1 cells have a ligand specificity very similar, if not identical, to that of V1a receptors. Vasopressin induced a marked (up to tenfold) increase in the production of labeled inositol phosphate (Ins 1,4,5 P3, Ins 1,4 P2, and Ins P) by WRK1 cells prelabeled with [3H]inositol. Antagonists of the vasopressor effect of vasopressin inhibited vasopressin-induced inositol lipid breakdown in WRK1 cells. For the entire series of vasopressin analogs tested, there was a close correlation between the respective Kd values for binding of these peptides to WRK1 cells and the corresponding Ka or Ki values derived from the determination of dose-dependent stimulation of inositol phosphate production, or inhibition of vasopressin-induced stimulation.