Cytoplasmic and nuclear signaling pathways of V1-vascular vasopressin receptors

We studied the cytoplasmic and nuclear signaling pathways of V1-vascular AVP receptors of human platelets, primary cultures of renal glomerular mesangial cells, and established cultures of the A7r5 aortic smooth muscle cell line. The immediate transmembrane signals are triggered by the formation of ligand-receptor complexes as illustrated by binding experiments with [3H]AVP (Kd = 2.50 nM), d(CH2)5Tyr(Me)AVP (Kd = 0.62 nM), the linear V1 antagonist phenylacetyl-D-Tyr(Et)-Phe-Val-Asn-Lys-Pro-[125I]Tyr-NH2 (Kd = 1.42 nM) or by fluorescence experiments with linear antagonists like phenylacetyl-D-Tyr(Et)-Phe-Gln-Asn-Lys-Pro-Arg-NH2 coupled to biotin and made fluorescent by labeling with tetramethylrhodamine-avidin. We used several approaches (radioreceptor binding, radioactive labeling, autoradiographic, enzymatic, photoaffinity labeling, and immunoblotting procedures) to identify the guanine nucleotide regulatory protein coupled to V1-vascular vasopressin receptors. AVP-stimulated GTPase activity of human platelet membranes was blocked by pretreatment with antibodies specific for the C-terminal of the newly described Gq alpha protein. In the presence of MgCl2, AVP increased labeling by the photoreactive GTP analog [alpha-32P]azidoanilido GTP of a platelet membrane protein of apparent molecular mass of 42 kDa. AVP effect was reversed by the specific V1-vascular antagonist d(CH2)5Tyr(Me)AVP and labeling was completely abolished by GTP gamma s.(ABSTRACT TRUNCATED AT 250 WORDS)