CALCIUM REGULATION OF ENDOTHELIAL PERMEABILITY TO LOW-DENSITY-LIPOPROTEIN

Increasing clinical and experimental evidence suggests a multifunction al role of calcium in determining the response of the arterial intima to atherogenic stimuli. In this study, an endothelial cell (EC)-smooth muscle cell (SMC) bilayer model of the arterial wall was used to inve stigate the effect of calcium manipulation on the sequestration of I-1 25-labeled LDL within the subendothelial space. Bilayer cell cultures were exposed to EGTA (0.25-2.0 mM), ionophore A23187 (5 X 10(-6) M), l anthanum chloride (0.1 mM), and trifluoperazine (TFP; 0.25 mu M). The movement of I-125-labeled LDL (10 mu g/ml) through the endothelial bar rier was measured, as was the binding and cellular uptake of I-125-lab eled LDL by each cell type. Extracellular Ca2+ chelation with EGTA and intracellular Ca2+ mobilization with A23187 both increased EC permeab ility to LDL (P < 0.05; P = 0.0001, respectively), while not significa ntly affecting EC binding or uptake of lipoprotein. Conversely, these agents increased SMC uptake of LDL (P < 10(-7); P < 10(-8), respective ly). Calcium blockade with lanthanum chloride had the opposite effect, reducing EC permeability (P = 0.011) and SMC uptake (P < 10(-5)), whi le increasing EC uptake (P = 0.016). TFP, a calmodulin inhibitor, had an effect similar to A23187, although reducing SMC uptake of LDL (P = 0.015). Alteration of the calcium gradient across the plasma membrane appears to influence EC permeability. This effect may be stabilized by Ca2+ blockade or calmodulin regulation of cytoplasmic Ca2+. Additiona l anti-atherogenic effects of calcium blockade may include a reduction in SMC uptake by the SMC. (C) 1995 Academic Press, Inc.