Atherogenic lipoproteins inhibit catecholamine secretion in cultured bovine adrenal medullary cells

The effects of lipoproteins on ion channel-mediated catecholamine secretion were investigated in cultured bovine adrenal medullary cells. Low density lipoprotein (LDL; 20–80 mg/dl) and lipoprotein(a) [Lp(a); 10–80 mg/dl] inhibited catecholamine secretion induced by carbachol, an activator of nicotinic acetylcholine receptor-ion channels. LDL and Lp(a) suppressed carbachol-induced 22 Na + influx as well as 45 Ca 2+ influx in a concentration-dependent manner similar to that of catecholamine secretion. The inhibition of catecholamine secretion by Lp(a) was not overcome by increasing the concentration of carbachol. On the other hand, high density lipoprotein (HDL; <150 mg/dl) had no effect on 22 Na + influx, 45 Ca 2+ influx, and catecholamine secretion. Like LDL and Lp(a), a synthetic peptide homologous to human plasma apolipoprotein B (apoB), apoB fragment 3358–3372 -amide (3–60 µM), attenuated 22 Na + influx, 45 Ca 2+ influx, and catecholamine secretion caused by carbachol. The apoB fragment also suppressed 22 Na + influx induced by veratridine (an activator of voltage-dependent Na + channels) and 45 Ca 2+ influx induced by 56 mM K + (an indirect activator of voltage-dependent Ca 2+ channels). These findings suggest that atherogenic lipoproteins such as LDL and Lp(a) suppress catecholamine secretion by interfering with Na + influx through nicotinic acetylcholine receptor-ion channels, in which apoB, a structural component common to both LDL and Lp(a), plays an important role. The inhibition by atherogenic lipoproteins of catecholamine secretion may influence the progression of atherosclerosis induced by these lipoproteins.