Human retinal pigment epithelial cells possess v₁ vasopressin receptors

Membrane preparations of cultured human retinal pigment epithelial (RPE) cells were incubated with various concentrations of [³H]arginine vasopressin (AVP) in the presence and absence of 10 uM nonradioactive AVP. Saturable, specific binding to a single site with a K_d of 6.2 nM and ^Bmax of 111 fmol/mg protein was detected. Vaaopressin had no effect on RPE cyclic AMP levels measured by radioimmunoassay. Intracellular calcium fluxes were measured by spectrofluorometry of RPE cell suspensions preloaded with quin 2. The baseline cytosolic calcium level was 217 ± 20 nM, and AVP caused a concentration-dependent increase in this level with a 3.5-fold maximal response at 10-^-6 M and an EC₅₀ of 120 nM. The production of inositol phosphates was measured in RPE preloaded with [³H]myoinositol, and AVP caused a concentration-dependent increase in their production with a 2.1-fold maximal response at 10-^-5 M and an EC₅₀ of 80 nM. A specific vasopressin receptor antagonist, SKF 101926, prevented the AVP-induced increase in calcium mobilization and ionistol phosphate production in RPE. These data suggest that RPE cells possess V₁ AVP receptors coupled to calcium mobilization and inositol phosphate metabolism.