Venter H, Genade S, Mouton R, Huisamen B, Harper I S, Lochner A
Department of Medical Physiology and Biochemistry, University of Stellenbosch Medical School, Tygerberg, Republic of South Africa.
J Mol Cell Cardiol. 1991 Nov;23(11):1271-86. doi: 10.1016/0022-2828(91)90084-y.
Evidence has recently been presented that myocardial ischaemia is associated with a significant increased mitochondrial cholesterol content, suggesting a redistribution of cholesterol within the ischaemic cell (Rouslin et al. 1980, 1982). The aim of this study was therefore to determine the effects of different periods of ischaemia and reperfusion on the cholesterol content of myocardial mitochondria, sarcoplasmic reticulum and sarcolemma. Using the isolated perfused rat heart as experimental model, it was demonstrated that increasing periods of ischaemia (15-60 min) caused a progressive loss of cholesterol from the tissue as well as from the sarcolemma and sarcoplasmic reticulum, concomitant with a significant increase in mitochondrial cholesterol content. These compositional changes were associated with a marked increase in sarcolemmal and mitochondrial microviscosity, while that of the sarcoplasmic reticulum was reduced. To gain more insight into the mechanisms controlling intracellular cholesterol distribution, control and ischaemic hearts were perfused with either exogenous cholesterol or its precursor [U-14C]acetate as an indicator of endogenous cholesterol synthesis. Perfusion with exogenous cholesterol resulted in significant increases in the membrane cholesterol content of control hearts. However, hypoxic, low flow perfusion prevented cholesterol enrichment of the sarcolemmal and sarcoplasmic reticulum membranes, while the cholesterol content of the mitochondria was increased from 99.48 +/- 12.75 to 127.61 +/- 1.84 nmols/mg protein, indicating specific incorporation into this membrane system. Incorporation of [U-14C]acetate into cholesterol in the sarcoplasmic reticulum was increased by 120% in ischaemic conditions. However, a marked redistribution of newly synthesized cholesterol was observed within the ischaemic cell: under control conditions most of the labelled cholesterol was transferred to the sarcolemma and least to the mitochondria, while this distribution pattern was reversed in ischaemia. In view of the fact that exchange of cholesterol between membranes is affected by both phospholipid polar head-group composition and acyl chain length and saturation, it is suggested that prior ischaemia-induced membrane compositional changes might lead to intracellular cholesterol redistribution. Finally, to determine whether cholesterol loss affects sarcolemmal permeability, hearts enriched in sarcolemmal cholesterol were subjected to 15 or 30 min global ischaemia followed by reperfusion and the rate of enzyme release determined. However, enzyme release was similar in treated and untreated hearts, indicating that sarcolemmal cholesterol loss probably does not affect its permeability.
最近有证据表明，心肌缺血与线粒体胆固醇含量显著增加有关，这表明缺血细胞内胆固醇发生了重新分布（罗斯林等人，1980年，1982年）。因此，本研究的目的是确定不同时长的缺血和再灌注对心肌线粒体、肌浆网和肌膜胆固醇含量的影响。以离体灌注大鼠心脏作为实验模型，结果表明，缺血时间延长（15 - 60分钟）会导致组织以及肌膜和肌浆网中的胆固醇逐渐流失，与此同时线粒体胆固醇含量显著增加。这些成分变化与肌膜和线粒体微粘度显著增加有关，而肌浆网的微粘度则降低。为了更深入了解控制细胞内胆固醇分布的机制，用外源性胆固醇或其前体[U - 14C]乙酸盐灌注对照心脏和缺血心脏，作为内源性胆固醇合成的指标。用外源性胆固醇灌注导致对照心脏的膜胆固醇含量显著增加。然而，缺氧、低流量灌注阻止了肌膜和肌浆网膜的胆固醇富集，而线粒体的胆固醇含量从99.48±12.75增加到127.61±1.84纳摩尔/毫克蛋白，表明胆固醇特异性地掺入了这个膜系统。在缺血条件下，[U - 14C]乙酸盐掺入肌浆网胆固醇的量增加了120%。然而，在缺血细胞内观察到新合成胆固醇的明显重新分布：在对照条件下，大部分标记胆固醇转移到肌膜，转移到线粒体的最少，而在缺血时这种分布模式发生了逆转。鉴于膜之间胆固醇的交换受磷脂极性头部基团组成以及酰基链长度和饱和度的影响，有人提出，先前缺血诱导的膜成分变化可能导致细胞内胆固醇重新分布。最后，为了确定胆固醇流失是否影响肌膜通透性，对富含肌膜胆固醇的心脏进行15或30分钟全心缺血，然后再灌注，并测定酶释放速率。然而，处理过的心脏和未处理的心脏的酶释放情况相似，这表明肌膜胆固醇流失可能不会影响其通透性。
