OXIDIZED LOW-DENSITY-LIPOPROTEIN (LDL) AND PLATELET INTRACELLULAR CALCIUM - INTERACTION WITH NITRIC-OXIDE

The present study tested the effects of ox-low density lipoprotein (LD L) on nitric oxide (NO)-dependent decrease in agonist-stimulated [Ca2](i), The effects of ox-LDL on platelet aggregation were also evaluate d. Platelets loaded with FURA 2 AM (2 mu mol/litre) were incubated wit h NO-donors for 2-10 min to obtain a 40-50% reduction in [Ca2+](i) and with NO-donors plus ox-LDL (100 mu g of protein/ml). Thrombin (0.03 U /ml) was used as an agonist, In some experiments 8-Br-cGMP (0.5-1 mmol /l) was used to investigate the NO-dependent intraplatelet signalling system. Slightly oxidized LDL was obtained by leaving native LDL in th e light at room temperature for at least 7 days, Ox-LDL did not cause any increase in thrombin-induced [Ca2+](i) (control: 215.4 +/- 44.3 nm ol/l, ox-LDL 223.4 +/- 35.3 nmol/l, M +/- SEM; n = 8) and platelet agg regation (control: 78.7 +/- 4.9%, ox-LDL: 78.9 +/- 4.2%, n = 12), Ox-L DL antagonized the effects of NO-donors on platelet [Ca2+](i) (NO-dono r: 137.4 + 22.1 nmol/l, NO + ox-LDL: 177.3 +/- 27.6 nmol/l, n = 11; P < 0.001) and platelet aggregation (NO-donor: 15.4 +/- 3.4%, NO + ox-LD L: 28.9 +/- 3.8%, n = 24; P < 0.001), Ox-LDL did not affect the inhibi tory activities of 8-Br-cGMP on platelet aggregation (8-Br-cGMP: 22.0 +/- 8.5 %, 8-Br-cGMP + ox-LDL: 19.3 +/- 7.8 %, n = 5) and platelet [Ca 2+](i), In conclusion, slightly oxidized LDL does not directly activat e platelets and does not affect the intracellular NO-dependent signall ing system. The present results suggest that LDL reduces the antiplate let activity of NO mainly by preventing its biological effects.