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High density lipoproteins increase cytoplasmic free calcium in bovine aortic endothelial cells
1Research Section of Pharmacology, Hunan Medical University, Changsha, People's Republic of China.
Insights
Human high density lipoproteins (HDL) cause a two-phase increase in intracellular calcium in bovine aortic endothelial cells (BAECs). Both internal and external calcium stores contribute to this HDL-induced calcium elevation.
Area of Science:
- Biochemistry
- Cell Biology
- Cardiovascular Research
Background:
- High-density lipoproteins (HDL) play a crucial role in reverse cholesterol transport.
- Endothelial cells are vital for vascular health and are influenced by lipoproteins.
- Intracellular calcium signaling is fundamental to cellular function and regulation.
Purpose of the Study:
- To investigate the effect of human HDL on intracellular calcium levels in cultured bovine aortic endothelial cells (BAECs).
- To elucidate the sources of calcium involved in HDL-mediated signaling in BAECs.
Main Methods:
- Cultured BAECs were treated with varying concentrations of human HDL.
- Intracellular calcium concentration ([Ca2+]i) was measured using the fluorescent indicator Fura-2.
- Experiments involved manipulating extracellular calcium levels and using calcium channel blockers (NiCl2) and release inhibitors (tetracaine).
Main Results:
- HDL induced a biphasic elevation of [Ca2+]i in BAECs, comprising a transient peak and a sustained phase.
- HDL-mediated calcium increases were dose-dependent (25-200 µg/mL).
- The sustained calcium component required extracellular calcium and was blocked by NiCl2, while tetracaine attenuated the response, indicating involvement of both intracellular and extracellular calcium pools.
Conclusions:
- Human HDL significantly influences intracellular calcium dynamics in BAECs.
- Both intracellular calcium stores and extracellular calcium influx contribute to the biphasic calcium elevation induced by HDL.
- These findings highlight a novel mechanism of HDL action in endothelial cells.
Abstract:
This study examined the influence of human high density lipoproteins (HDL) on the intracellular free calcium of cultured bovine aortic endothelial cells (BAECs). Intracellular Ca2+ concentration ([Ca2+]i) was determined by a fluorescent calcium indicator, Fura-2. It was found that, in the presence of 1 mmol/L extracellular calcium, HDL resulted in a biphasic elevation of [Ca2+]i in BAECs, consisting of an initial, transient component followed by a lower, but more sustained component. Doses of HDL from 25 to 200 micrograms protein/ml induced marked concentration-dependent elevations of [Ca2+]i in BAECs. The sustained component was abolished by deprivation of extracellular calcium or by pretreatment of endothelial cells with a calcium influx blocker, NiCl2, HDL-induced elevation of [Ca2+]i was attenuated in a concentration-dependent way by an inhibitor of calcium release, tetracaine. Repeated applications of HDL (100 micrograms protein/ml) markedly blunted the initial peak component of the calcium transient of BAECs. These results demonstrate that both intracellular and extracellular calcium pools are responsible for the biphasic elevation of [Ca2+]i induced by HDL in cultured BAECs.