Enhancement of vascular action of arginine vasopressin by diminished extracellular sodium concentration

The present study was undertaken to examine the effects of diminished extracellular sodium concentration on the vascular action of arginine vasopressin (AVP) in cultured rat vascular smooth muscle cells (VSMC). The preincubation of cells with the 110 mM extracellular Na+ (Na+]e) solution supplemented with 30 mM choline chloride for 60 minutes enhanced the effect of AVP- (1 x 10(-8) M) induced VSMC contraction. The treatment of 110 mM Na+]e solution also enhanced the cellular contractile response to the protein kinase C (PKC) activators, phorbol 12-myristate 13-acetate and 1-oleoyl-2-acetyl-glycerol. Furthermore, preincubation with the 110 mM Na+]e solution also potentiated the effect of 1 x 10(-8) M AVP, but not 1 x 10(-6) M, to increase the cytosolic-free Ca2+ (Ca2+]i) concentration. The 110 mM Na+]e media decreased the basal intracellular Na+ concentration and increased intracellular 45Ca2+ accumulation, basal Ca2+]i and AVP-produced 45Ca2+ efflux. These effects of 110 mM Na+]e solution to enhance the vascular action of AVP were abolished by using Ca(2+)-free 110 mM Na+]e solution during the preincubation period. The preincubation with the 110 mM Na+]e solution did not change either the Kd and Bmax of AVP V1 receptor of VSMC or the AVP-induced production of inositol 1,4,5-trisphosphate. The present in vitro results therefore indicate that the diminished extracellular fluid sodium concentration within a range observed in clinical hyponatremic states enhances the vascular action of AVP.(ABSTRACT TRUNCATED AT 250 WORDS)