Modulation of nonselective cation current by oxidized LDL and lysophosphatidylcholine and its inhibitory contribution to endothelial damage

Aims: This study examined the effects of oxidized low-density lipoprotein (LDL) and its major lipid constituent lysophosphatidylcholine (LPC) on nonselective cation (NSC) current and its inhibitory contribution to LPC-induced cytotoxicity in cultured human umbilical endothelial cells (HUVECs). Main methods: Patch-clamp technique and the resazurin-based cell viability assay were used. Key findings: In voltage-clamped cells, oxidized LDL or LPC slowly activated NSC current. NSC current was also activated by loading cells with Ca²⁺ solution buffered at various concentrations using a patch pipette or by applying the sarcoplasmic reticulum Ca²⁺ pump blocker 2,5-di-t-butyl-1,4-benzohydroquinone (BHQ), the metabolic inhibitor CN^- or the hydroperoxide donor tert-butyl hydroperoxide (TBHP). On the contrary, when intracellular Ca²⁺ was strongly buffered with 12mM BAPTA or cells were loaded with superoxide dismutase using a patch pipette, LPC or BHQ did not activate NSC current. Furthermore, NSC current activated by LPC, TBHP or CN^- was inhibited by the antioxidant tempol or extracellular Ca²⁺ depletion and NSC current activated by intracellular Ca²⁺ was further augmented by oxidized LDL or LPC. LPC or oxidized LDL released Ca²⁺ from intracellular stores and further enhanced store-operated Ca²⁺ entry. LPC-induced cytotoxicity was augmented by inhibiting Ca²⁺ influx and NO synthesis. Significance: Oxidized LDL or its main component LPC activated Ca²⁺-permeable NSC current via releasing Ca²⁺ from intracellular stores and producing ROS and thereby increased Ca²⁺ influx. Ca²⁺ influx through NSC channel might protect endothelial cells by producing NO.