ROLE OF ENDOTHELIUM-DERIVED NITRIC-OXIDE IN STIMULATION OF NA+-K+-ATPASE ACTIVITY BY ENDOTHELIN IN RABBIT AORTA

An endothelium-derived factor with the properties of nitric oxide (NO) has recently been implicated in the regulation of basal Na+-K+-adenosinetriphosphatase (ATPase) activity in vascular smooth muscle. To determine whether this factor also plays a role in the stimulation of ouabain-sensitive (OS) Rb-86 uptake by specific agonists, studies were carried out using rabbit aortic rings. In endothelium-intact rings incubated for 3 h with Krebs-Henseleit solution containing 5.5 mM glucose, endothelin (ET) caused a concentration-dependent increase in OS Rb-86 uptake (maximal increase = 205%, with 100 nM ET). Incubation with phenylephrine (Phe; 0.1 and 1 mu M) or phorbol 12,13-dibutyrate (PDBu; 0.1 CLM), under the same conditions, increased OS Rb-86 uptake by 128, 144, and 140%, respectively. Removal of endothelium before incubation decreased the ability of ET to stimulate OS Rb-86 uptake by 38-45%, but it did not diminish the stimulation of OS Rb-86 uptake by Phe or PDBu. An increase in the concentration of glucose from 5.5 to 44 mM diminished ET-stimulated OS Rb-86 uptake by 50% in endothelium-intact rings but had no effect on Phe- or PDBu-induced increases in OS Rb-86 uptake. Addition of the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA; 0.3 mM) to the medium decreased ET-stimulated OS Rb-86 uptake by 40%. Guanosine 3',5'-cyclic monophophate (cGMP) formation in endothelium-intact rings was also increased (65%) by ET but not by Phe or PDBu. The increase in cCMP by ET was totally inhibited by L-NMMA or endothelium denudation. These results indicate that the stimulation of Na+-K+-ATPase activity in the rabbit aorta by ET is in part endothelium dependent. They suggest that ET acts by increasing the release of NO and that this component of its effect on aortic Na+-K+-ATPase activity is inhibited by hyperglycemia.