Oxidized Low-density Lipoprotein- and Lysophosphatidylcholine-induced Ca2+ Mobilization in Human Endothelial Cells

Abstract

The effects of oxidized low-density lipoprotein (OxLDL) and its major lipid constituent lysophosphatidylcholine (LPC) on Ca(2+) entry were investigated in cultured human umbilical endothelial cells (HUVECs) using fura-2 fluorescence and patch-clamp methods. OxLDL or LPC increased intracellular Ca(2+) concentration ([Ca(2+)](i)), and the increase of [Ca(2+)](i) by OxLDL or by LPC was inhibited by La(3+) or heparin. LPC failed to increase [Ca(2+)](i) in the presence of an antioxidant tempol. In addition, store-operated Ca(2+) entry (SOC), which was evoked by intracellular Ca(2+) store depletion in Ca(2+)-free solution using the sarcoplasmic reticulum Ca(2+) pump blocker, 2, 5-di-t-butyl-1, 4-benzohydroquinone (BHQ), was further enhanced by OxLDL or by LPC. Increased SOC by OxLDL or by LPC was inhibited by U73122. In voltage-clamped cells, OxLDL or LPC increased [Ca(2+)](i) and simultaneously activated non-selective cation (NSC) currents. LPC-induced NSC currents were inhibited by 2-APB, La(3+) or U73122, and NSC currents were not activated by LPC in the presence of tempol. Furthermore, in voltage-clamped HUVECs, OxLDL enhanced SOC and evoked outward currents simultaneously. Clamping intracellular Ca(2+) to 1 microM activated large-conductance Ca(2+)-activated K(+) (BK(Ca)) current spontaneously, and this activated BK(Ca) current was further enhanced by OxLDL or by LPC. From these results, we concluded that OxLDL or its main component LPC activates Ca(2+)-permeable Ca(2+)-activated NSC current and BK(Ca) current simultaneously, thereby increasing SOC.