Cholesterol enrichment inhibits Na+/K+ pump in endothelial cells.
We have previously shown that cholesterol enrichment reduces 3H-ouabain binding in cultured vascular endothelial cells. The present study aimed to determine the effect of cholesterol enrichment on ouabain-sensitive 86Rb (as a substitute for K+) influx, i.e. K+ transport via the pump, and to examine whether cellular K+ content was affected in human umbilical vein endothelial cells. 86Rb influx was inhibited by both ouabain and bumetanide in a dose-dependent manner. Consistent with an earlier report [1], inhibition achieved was greater for ouabain (approximately 70% at mM range) than for bumetanide (approximately 55% at 0.1 mM), indicating that K+ influx via Na+/K+ pump was greater than that via Na(+)-K(+)-Cl- cotransport in these cells. After incubation of 18 h or more with cholesterol-enriched liposomes (2:1 cholesterol to phospholipid ratio), a significant reduction (> 20%) of the ouabain-sensitive K+ influx and an increase in cellular cholesterol content were observed. The inhibitory effect was observed only at liposome concentrations above 2 mg/ml. Following 18 h incubation with 2 mg/ml cholesterol-enriched liposomes, cellular K+ content was significantly decreased. The phospholipid liposome treatment did not alter K+ content, suggesting that the inhibitory effect on Na+/K+ pump and the cellular K+ content reduction was not due to liposome fusion alone or to the phospholipid present. These findings indicate that cholesterol enrichment inhibits Na+/K+ pump and thus reduces cellular K+ content in endothelial cells, and may play a role in the widely observed abnormal endothelium-dependent vascular response induced by hypercholesterolemia.
Department of Physiology, Chang Gung Medical College, Taiwan, R.O.C.
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YT
Lau
D002034:Bumetanide / Q000494:pharmacology; D002478:Cells, Cultured; D002784:Cholesterol / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000378:metabolism*; D006801:Humans; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014471:Umbilical Veins
D002034:Bumetanide; D010042:Ouabain; D002784:Cholesterol; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium