Sokoya Elke M, Burns Alan R, Marrelli Sean P, Chen Jie
Department of Anesthesiology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
Microvasc Res. 2007 Jul;74(1):39-44. doi: 10.1016/j.mvr.2007.03.003. Epub 2007 Apr 6.
Previous findings from our laboratory have shown that dilations to endothelium-derived hyperpolarizing factor (EDHF) in rat middle cerebral artery (MCA) are less in females compared to males. Myoendothelial gap junctions (MEGJs) appear to mediate the transfer of hyperpolarization between endothelium and smooth muscle in males. In the present study, we hypothesized that MEGJs are the site along the EDHF pathway which is compromised in female rat MCA. Membrane potential in endothelium was measured using the voltage-sensitive dye di-8-ANEPPS and in smooth muscle using intracellular glass microelectrodes in the presence of l-NAME (3x10(-5 )M) and indomethacin (10(-5 )M). Electron microscopy was used to assess MEGJ characteristics. In endothelial cells, the di-8-ANEPPS fluorescence ratio change to 10(-5 )M UTP was similar in males (-2.9+/-0.5%) and females (-3.2+/-0.2%), indicating comparable degrees of endothelial cell hyperpolarization. However, smooth muscle cell hyperpolarization to 10(-5 )M UTP was significantly attenuated in females (0 mV hyperpolarization; -31+/-1.5 mV resting) compared to males (8 mV hyperpolarization; -28+/-1.7 mV resting). Ultrastructural evidence suggested that MEGJ frequency and area of contact were comparable between males and females. Taken together, our data suggest that in rat MCA, MEGJ frequency does not account for the reduced EDHF responses observed in females compared to males. We conclude that reduced myoendothelial coupling and/or homocellular coupling within the media may account for these differences.
我们实验室之前的研究结果表明，与雄性大鼠相比，雌性大鼠大脑中动脉（MCA）对内皮源性超极化因子（EDHF）的扩张反应较小。肌内皮间隙连接（MEGJs）似乎介导了雄性大鼠内皮和平滑肌之间的超极化传递。在本研究中，我们假设MEGJs是EDHF通路中受损的部位，这一部位在雌性大鼠MCA中表现更为明显。在存在L-精氨酸甲酯（l-NAME，3×10⁻⁵ M）和吲哚美辛（10⁻⁵ M）的情况下，使用电压敏感染料di-8-ANEPPS测量内皮中的膜电位，使用细胞内玻璃微电极测量平滑肌中的膜电位。采用电子显微镜评估MEGJ的特征。在内皮细胞中，雄性（-2.9±0.5%）和雌性（-3.2±0.2%）对10⁻⁵ M三磷酸尿苷（UTP）的di-8-ANEPPS荧光比率变化相似，表明内皮细胞超极化程度相当。然而，与雄性（超极化8 mV；静息电位-28±1.7 mV）相比，雌性对10⁻⁵ M UTP的平滑肌细胞超极化明显减弱（超极化0 mV；静息电位-31±1.5 mV）。超微结构证据表明，雄性和雌性之间MEGJ的频率和接触面积相当。综上所述，我们的数据表明，在大鼠MCA中，MEGJ频率并不能解释与雄性相比雌性中观察到的EDHF反应降低的现象。我们得出结论，中膜内肌内皮耦合和/或同细胞耦合的减少可能是造成这些差异的原因。
