Atherogenic lipoproteins inhibit catecholamine secretion in cultured bovine adrenal medullary cells

Abstract

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 ²²Na⁺ influx as well as ⁴⁵Ca²⁺ 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 ²²Na⁺ influx, ⁴⁵Ca²⁺ 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 ²²Na⁺ influx, ⁴⁵Ca²⁺ influx, and catecholamine secretion caused by carbachol. The apoB fragment also suppressed ²²Na⁺ influx induced by veratridine (an activator of voltage-dependent Na⁺ channels) and ⁴⁵Ca²⁺ influx induced by 56 mM K⁺ (an indirect activator of voltage-dependent Ca²⁺ 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.