MILDLY OXIDIZED LDL EVOKES A SUSTAINED CA2-DEPENDENT RETRACTION OF VASCULAR SMOOTH-MUSCLE CELLS()

Oxidized low density lipoprotein (LDL) is thought to play a major role in atherogenesis. Atherosclerotic arteries exhibit structural changes associated with profound alterations in vascular tone that are potent ially involved in arterial spasm and ischemic heart disease. We report here the role of oxidized LDL in the retraction of vascular smooth mu scle cells. Mildly oxidized LDL elicited a broad and sustained peak in cytosolic calcium concentration ([Ca2+](i)) in cultured arterial smoo th muscle cells. Concomitant with the [Ca2+](i) rise, oxidized LDL evo ked a sustained and intense retraction of smooth muscle cells, as show n by the changes in cross-sectional area of single cells. Cell retract ion was dependent on time, the concentration of oxidized LDL, and the level of LDL oxidation (native LDL induced neither a significant [Ca2](i) rise nor cell retraction). Oxidized LDL but not native LDL also e licited a delayed (12+/-2 hours) and sustained (14+/-2 hours) increase in isometric tension in deendothelialized arterial rings only, thus s uggesting a protective role of intact endothelium. When triggered by n ontoxic doses of oxidized LDL, retraction of cultured cells and the co ntractile response of aortic rings was reversible, whereas with higher (toxic) doses (greater than or equal to 200 mu g apoB/mL), cell retra ction was irreversible and led progressively to detachment and cell de ath. Cell retraction can be prevented in three ways: (1) by inhibiting LDL oxidation with supplements of antioxidants (indirect inhibition); (2) by blocking the pathogenic intracellular signaling elicited by ox idized LDL (direct inhibition), eg, by inhibiting calcium influx with EGTA or the calcium channel blocker nisoldipine or by blocking intrace llular signaling (at a still-unknown step) by the lipophilic antioxida nt alpha-tocopherol; and (3) by directly inhibiting myosin light chain kinase by aphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine. In concl usion, oxidized LDL evoked a sustained and intense calcium-dependent r etraction of cultured smooth muscle cell, which can be prevented by in hibiting LDL oxidation or by blocking the intracellular signaling indu ced by oxidized LDL.