Rat thymocyte sodium transport. Effects of changes in sodium balance and experimental hypertension.

Abstract

SUMMARY The wide range of membrane electrolyte transport abnormalities associated with experimental, genetic, and essential hypertension may either reflect an underlying global change in the cell membrane or may be directly related to the underlying disturbance that causes hypertension or to changes in sodium balance. To investigate this further, we studied sodium transport and intracellular electrolyte composition in the thymocytes of normal rats undergoing salt loading or depletion, and in rats with renovascular, mineralocorticoid, or spontaneous hypertension compared to appropriate age-matched normotensive control rats. In normotensive rats, although there was no significant difference between the blood pressures at the two extremes of sodium balance, sodium loading caused a nonsignificant rise in sodium transport, whereas sodium depletion was associated with a significant fall in sodium transport and intracellular sodium. When cells from salt-loaded or normal animals were incubated in a medium containing their own serum, sodium transport was slightly stimulated in both, but there was no significant difference in the sodium efflux-rate constant of thymocytes obtained from rats on the normal as opposed to the high salt intake. Compared to normotensive rats, there was no significant change in the sodium efflux-rate constant in any of the hypertensive rat models studied. However, the sodium efflux-rate constant fell with age in both the spontaneously hypertensive and Wistar-Kyoto normotensive rats. The present studies show that dietary sodium intake and aging had considerable effects on rat thymocyte sodium transport, but neither of these changes was related to a change in blood pressure. Moreover, the raised blood pressure that developed in genetic, renovascular, and mineralocorticoid hypertension was not associated with a significant change in sodium transport. These experiments suggest that the currently described changes in membrane electrolyte transport of cells not directly involved in blood pressure control, in association with hypertension, probably reflect a fundamental change in the cell membrane. This change may not necessarily be related to the raised blood pressure. Further, sodium depletion, rather than sodium loading, produces inhibition of active sodium pumping in this cell. (Hypertension 6: 454-459, 1984)

Is calcium more important than sodium in the pathogenesis of essential hypertension?

“…In contrast, the same investigators could detect neither a change in intracellular sodium content nor pump activity in one-kidney, one clip hypertensive rats. 215 The DOCA salt-sensitive rats exhibit a decrease in intracellular sodium content, though their efflux rate constants are similar. Other observers have demonstrated reduction in the Na,KATPase activity of this model.…”

“…214 Less is known about intracellular sodium content in salt-induced or volume-dependent hypertensive models. 196 - 215 In normal rats fed high sodium diets to induce volume expansion, there is no change in intracellular sodium. 215 Nor is there any change in thymocyte sodium content in two-kidney, one clip hypertension, even though Na,K-ATPase is reduced.…”

“…196 - 215 In normal rats fed high sodium diets to induce volume expansion, there is no change in intracellular sodium. 215 Nor is there any change in thymocyte sodium content in two-kidney, one clip hypertension, even though Na,K-ATPase is reduced. In contrast, the same investigators could detect neither a change in intracellular sodium content nor pump activity in one-kidney, one clip hypertensive rats.…”

Lymphocyte abnormalities in three types of hypertension in the rat.

“…Jones et al l6 reported that T lymphocytes from spontaneously hypertensive rats exhibited higher sodium content and a decrease in the rate constant for total sodium efflux (active and passive combined) as compared with normotensive controls. Bradlaugh et al, 17 however, did not find a significant difference in sodium rate constants (active or passive) of lymphocytes from spontaneously hypertensive rats and normotensive rats. These investigators have presented evidence that suggests that the decreased sodium efflux rate constant observed by Jones et al 16 is attributable to age of the rat rather than to the blood pressure elevation of spontaneously hypertensive rats.…”

“…14 Although, as far as we know, there have not been any reported studies of peripheral blood lymphocytes of rats, Jones et al 16 and Bradlaugh et al 17 have examined sodium content and transport in thymocytes (T lymphocytes) derived from the rat thymus gland. Jones et al l6 reported that T lymphocytes from spontaneously hypertensive rats exhibited higher sodium content and a decrease in the rate constant for total sodium efflux (active and passive combined) as compared with normotensive controls.…”