School of Biomedical Sciences, University of Queensland, St. Lucia, Australia.
Endocrinology. 2012 Nov;153(11):5480-90. doi: 10.1210/en.2012-1404. Epub 2012 Sep 4.
Ischemic heart diseases often induce cardiac arrhythmia with irregular cardiac action potential (AP). This study aims to demonstrate that GH secretagogues (GHS) ghrelin and its synthetic analog hexarelin can preserve the electrophysiological properties of cardiomyocytes experiencing ischemia/reperfusion (I/R). Isolated hearts from adult male mice underwent 20 min global ischemia followed by 30 min reperfusion using a Langendorff apparatus. Ghrelin (10 nM) or hexarelin (1 nM) was administered in the perfusion solution either 10 min before or after ischemia, termed pre- or posttreatments. Cardiomyocytes isolated from these hearts were used for whole-cell patch clamping to measure AP, voltage-gated L-type calcium current (I(CaL)), transient outward potassium current (I(to)), and sodium current (I(Na)). AP amplitude and duration were significantly decreased by I/R, but GHS treatments maintained their normality. GHS treatments prevented the decrease in I(CaL) and I(Na) after I/R, thereby maintaining AP amplitude. Although the significant increase in I(to) after I/R partially explained the shortened AP duration, the normalization of it by GHS treatments might contribute to the preservation of AP duration. Phosphorylated p38 and c-Jun NH(2)-terminal kinase and the downstream active caspase-9 in the cellular apoptosis pathway were significantly increased after I/R but not when GHS treatments were included, whereas phosphorylation of ERK1/2 associated with cell survival showed increase after I/R and a further increase after GHS treatments by binding to its receptor GHS receptor type 1a. These results suggest GHS can not only preserve the electrophysiological properties of cardiomyocytes after I/R but also inhibit cardiomyocyte apoptosis and promote cell survival by modification of MAPK pathways through activating GHS receptor type 1a.
缺血性心脏病常引起心律失常，表现为不规则的心肌动作电位（AP）。本研究旨在证明 GH 促分泌素（GHS）ghrelin 及其合成类似物 hexarelin 可维持经历缺血/再灌注（I/R）的心肌细胞的电生理特性。成年雄性小鼠的心脏通过 Langendorff 仪器进行 20 分钟的整体缺血，然后进行 30 分钟的再灌注。在缺血前 10 分钟或缺血后给予 ghrelin（10 nM）或 hexarelin（1 nM）灌注液，分别称为预处理或后处理。从这些心脏分离的心肌细胞用于全细胞膜片钳测量 AP、电压门控 L 型钙电流（I（CaL））、瞬时外向钾电流（I（to））和钠电流（I（Na））。AP 幅度和持续时间在 I/R 后显著降低，但 GHS 处理使其正常化。GHS 处理可防止 I/R 后 I（CaL）和 I（Na）的减少，从而维持 AP 幅度。尽管 I/R 后 I(to)的显著增加部分解释了 AP 持续时间的缩短，但 GHS 处理对其正常化可能有助于维持 AP 持续时间。细胞凋亡途径中磷酸化的 p38 和 c-Jun NH2-末端激酶以及下游活性 caspase-9 在 I/R 后显著增加，但当包含 GHS 处理时则不会增加，而与细胞存活相关的 ERK1/2 的磷酸化在 I/R 后增加，并在 GHS 处理后通过与 GHS 受体类型 1a 结合而进一步增加。这些结果表明，GHS 不仅可以在 I/R 后维持心肌细胞的电生理特性，还可以通过激活 GHS 受体类型 1a 来调节 MAPK 途径，从而抑制心肌细胞凋亡并促进细胞存活。
