SEX-HORMONES AFFECT THE CALCIUM SIGNALING RESPONSE OF HUMAN ARTERIAL CELLS TO LDL

The present study was designed to examine the role of calcium-dependen t signal transduction as a common link between the atherogenic effect of LDL and the mitigating influence of sex hormones in aortic endothel ial (EC) and smooth muscle cells (SMC). Human aortic EC and SMC were p reincubated for 48 hr in media containing no hormone, 17-beta-estradio l (20 ng/ml) or testosterone (300 ng/ml). Low density lipoprotein (N-L DL) or its minimally oxidized species (Ox-LDL) was added to the media at different concentrations (0, 2, 5, 10, 20, and 40 mu g protein/ml), and changes in cytosolic calcium [Ca+2](i) were measured by spectrofl uorometric analysis using a Fura 2-AM indicator. Cell viability was de termined with a (51)chromium release assay. In EC, exposure to N-LDL r esulted in a weak and unsustained increase in [Ca+2](i), (max. 21.9 +/ - 4.6%) while a more marked rise was seen in SMC (max. 79.1 +/- 11.5%; P < 0.005). There was an amplified response to the more atherogenic O x-LDL in both EC (max. 130.9 +/- 22.9%) and SMC (max. 240.5 +/- 14.2%; P < 0.0002). Estrogen was associated with a lower resting level of [C a+2](i) in both cell types, and resulted in a significant, dose-depend ent inhibition of cytosolic calcium mobilization in SMC exposed to Ox- LDL (P < 0.05). Alternatively, testosterone increased cytosolic calciu m response in SMC exposed to either N-LDL (P < 0.05) or Ox-LDL (P < 0. 05). Similar trends were seen in EC, but failed to reach statistical s ignificance. These changes could not be attributed to cell toxicity. S ex hormones may modulate the atherogenic potential of LDL by influenci ng intracellular, calcium-dependent Signaling mechanisms. (C) 1996 Aca demic Press, Inc.