Oxidized low-density lipoprotein- and lysophostidylcholine-induced Ca²⁺ mobilization in human endothelial cells

The effects of oxidized low-density lipoprotein (OxLDL) and its major lipid constituent lysophosphatidylcholine (LPC) on Ca²⁺ entry were investigated in cultured human umbilical endothelial cells (HUVECs) using fura-2 fluorescence and patch-clamp methods. OxLDL or LPC increased intracellular Ca²⁺ concentration ([Ca²⁺]_i), and the increase of [Ca²⁺]_i by OxLDL or by LPC was inhibited by La³⁺ or heparin. LPC failed to increase [Ca²⁺]_i in the presence of an antioxidant tempol. In addition, store-operated Ca²⁺ entry (SOC), which was evoked by intracellular Ca²⁺ store depletion in Ca²⁺-free solution using the sarcoplasmic reticulum Ca²⁺ pump blocker, 2, 5-di-t-butyl-1, 4-benzohydroquinone (BHQY), 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 [Ca²⁺]_i and simultaneously activated non-selective cation (NSC) currents. LPC-induced NSC currents were inhibited by 2-APB, La³⁺ 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. Clampinig intracellular Ca²⁺ to 1 υM activated large-conductance Ca²⁺-activated K⁺ (BK_Ca) clirrent spontaneously, and this activated BK_Ca current was further enhanced bv OxLDL or by LPC. From these results, we concluded that OxLDL or its main component LPC activates Ca²⁺-permeable Ca²⁺-activated NSC current and BK_Ca current simultaneously, thereby increasing SOC.