Kaoru Shirai

Effects of high-density lipoproteins on intracellular pH and proliferation of human vascular endothelial cells.

We investigated the effects of high-density lipoprotein (HDL) on the intracellular pH ([pH]i), and on the proliferation of human vascular endothelial cells (HUVEC), as well as on their production of prostacyclin (PGI2). The [pH]i was slightly acidified when extracellular Ca2+ was chelated with EGTA. Pretreatment of HUVEC with amiloride, the Na+/H+ exchange inhibitor, caused the [pH]i to become strongly acidic. The addition of HDL produced a biphasic shift in [pH]i, with a brief initial acidification followed by a rapid alkaline shift. The initial decrease in [pH]i was abolished in the cells pretreated with EGTA, and subsequent alkalinization was inhibited. The alkalinization of [pH]i disappeared in the cells pretreated with amiloride. These results suggest that [pH]i depends mainly on Na+/H+ exchange and partially on the extracellular Ca2+ of the HUVEC either in the resting unstimulated state or during HDL stimulation. In contrast, the addition of LDL produced an acidification of [pH]i, which was increased by LDL in the Ca(2+)-free condition. In the cells pretreated with amiloride, [pH]i was not further acidified by LDL. As a result, HDL promoted the proliferation of cells, an action that was inhibited by pretreatment with EGTA. However LDL inhibited cell proliferation, an action unaffected by EGTA pretreatment. The addition of HDL also enhanced the generation of prostacyclin in endothelial cells, the enhancement of PGI2 generation resulted from an increase in the release of Ca2+ from storage sites, due not only to an increased production of inositol 1,4,5-trisphosphate (IP3), but also to the alkalinization of [pH]i. These effects may be involved in the mechanism of HDLs anti-atherosclerotic action.

Effects of Intracellular pH on the Antithrombotic Properties of Human Vascular Endothelial Cells

Among the many events that occur in stimulated cells, there is always a significant shift in intracellular pH ([pH]i). The expression of some cellular responses after stimulation have been attributed to this pH shift. In neutrophils, stimulus-induced alkaline shifts in [pH]i have been proposed to modulate chemotaxis, aggregation, phagocytosis, secretion and the generation of superoxide radicals1)–3). In recent years, a convincing role for changes in [pH]i in the action of extracellular growth stimulation has been documented with a variety of cell types in culture4). However, the relationship between [pH], and the antithrombotic mechanisms of vascular endothelial cells has not been investigated. In the present study, the effects of [pH], on the antithrombotic properties of vascular endothelial cells were investigated utilizing human umbilical vein endothelial cells (HUVEC).