The long term objective of this project is to define the mechanisms underlying changes in Na. K-ATPase (NKA), or the Na-Pump (NaP), activity in vascular smooth muscle in development and maintenance of hypertension. Tail artery NaP activity, measured as ouabain-sensitive Rb uptake, shows tri- phasic changes in DOCA-salt hypertension. An endogenous inhibitor of the pump contributes to these changes. To determine whether the alterations in NaP are associated with changes in the kinetic properties of the vascular NaP, we will measure the km and V max of the vascular NaP during early, established, and late stages of DOCA-salt hypertension. We will also quantitate the NaP sites using a monoclonal antibody against NKA. An endogenous digitalis-like inhibitor(s) of the vascular NaP may be important in development and maintenance of hypertension. To further define the relationships between chronic exposure to a circulating NaP inhibitor, alterations in vascular NaP activity and development of hypertension, ASI- 222 (a polar analog of digitalis, 10 times more potent an inhibitor of NKA than digoxin) will be administered to inhibit chronically the vascular NaP. Preliminary experiments show that chronic iv administration of ASI-222 produces hypertension. Studies will be conducted to determine whether chronic exposure to a circulating NaP inhibitor produces hypertension and alterations in vascular NaP activity and NaP site density comparable to those seen in the DOCA-salt model, which is characterized by a circulating endogenous NaP inhibitor. There are two major limitations of the DOCA-salt hypertensive model in the study of NaP activity determinants; I) it is difficult to study the NKA enzyme activity in vascular tissue because the arteries contain small amounts of this enzyme, and 2) there are other confounding variables inherent to an in vivo system which complicate a focuses and in-depth study of vascular NaP function/NKA activity regulation by endogenous and/or exogenous inhibitors. To overcome these limitations, cultured vascular smooth muscle cells will be used to define the direct effects of chronic NaP inhibition on regulation of NaP/NKA. Effects of plasma or plasma extracts treated with DOCA-salt and ASI-222 will be compared. Additionally, effects or certain long-chain unsaturated fatty acids known to inhibit NKA, and which are possible candidate(s) for an endogenous inhibitor of the NaP, will be studied.
