In human hypercholesterolemia increased reactivity of vascular smooth muscle cells is due to altered subcellular Ca2+ distribution

There is evidence that, besides an attenuated endothelium-dependent relaxat ion, functional changes in smooth muscle contractility occur in experimenta l hypercholesterolemic animals. Unfortunately, little is known of the situa tion in human arteries, and the intracellular mechanisms involved in the mo dulation of vascular smooth muscle function in human hypercholesterolemia a re still unclear. Thus, besides acetylcholine-induced endothelium-dependent relaxation, smooth muscle reactivity to KCl, norepinephrine (NE) and pheny lephrine (PE) was evaluated in uterine arteries from 34 control individuals (CI) and 22 hypercholesterolemic patients (HC). Contractions to KCl, norep inephrine and phenylephrine were enhanced by 1.3-, 2.1- and 3.5-fold in ves sels from HC. Furthermore, the Ca2+ signaling in the perinuclear cytosol, w hich promotes cell, contraction, and that of the subplasmalemmal region, wh ich contributes to smooth muscle relaxation, were examined in freshly isola ted smooth muscle cells. In cells from HC, increases in perinuclear Ca2+ co ncentration ([Ca2+](peri)) in response to 30 mM KCl and 300 nM NE were incr eased by 67 and 93%, respectively. In contrast, the increase in the subplas malemmal Ca2+ concentration ([Ca2+](sub)) to 10 mu M NE was reduced in cell s from HC by 33%. No further differences in perinuclear and subplasmalemmal Ca2+ signaling were found in cultured smooth muscle cells from CI and HC ( primary culture 4-6 weeks after isolation). These data indicate a significa nt change in the subcellular Ca2+ distribution in smooth muscle cells from HC. In addition, production of superoxide anions (O-2(-)) was increased 3.8 -fold in uterine arteries from HC. Treatment of smooth muscle cells with th e O-2(-)-generating mixture xanthine oxidase/hypoxanthine mimicked hypercho lesterolemia on smooth muscle Ca2+ signaling. From these findings, we concl ude that during hypercholesterolemia, besides a reduced endothelium-depende nt relaxation, changes in smooth muscle reactivity take place. Thereby, smo oth muscle contractility is increased possibly due to the observed changes in subcellular Ca2+ signaling. The observed increased O-2(-) production in HC might play a crucial role in the alteration of smooth muscle function in hypercholesterolemia. (C) 2000 Elsevier Science Ireland Ltd. All rights re served.