Laboratory of Experimental Cardiology, University of Leuven, Leuven, Belgium.
PLoS One. 2011;6(10):e25100. doi: 10.1371/journal.pone.0025100. Epub 2011 Oct 13.
In ventricular myocytes of large mammals, not all ryanodine receptor (RyR) clusters are associated with T-tubules (TTs); this fraction increases with cellular remodeling after myocardial infarction (MI).
To characterize RyR functional properties in relation to TT proximity, at baseline and after MI.
Myocytes were isolated from left ventricle of healthy pigs (CTRL) or from the area adjacent to a myocardial infarction (MI). Ca(2+) transients were measured under whole-cell voltage clamp during confocal linescan imaging (fluo-3) and segmented according to proximity of TTs (sites of early Ca(2+) release, F>F(50) within 20 ms) or their absence (delayed areas). Spontaneous Ca(2+) release events during diastole, Ca(2+) sparks, reflecting RyR activity and properties, were subsequently assigned to either category.
In CTRL, spark frequency was higher in proximity of TTs, but spark duration was significantly shorter. Block of Na(+)/Ca(2+) exchanger (NCX) prolonged spark duration selectively near TTs, while block of Ca(2+) influx via Ca(2+) channels did not affect sparks properties. In MI, total spark mass was increased in line with higher SR Ca(2+) content. Extremely long sparks (>47.6 ms) occurred more frequently. The fraction of near-TT sparks was reduced; frequency increased mainly in delayed sites. Increased duration was seen in near-TT sparks only; Ca(2+) removal by NCX at the membrane was significantly lower in MI.
TT proximity modulates RyR cluster properties resulting in intracellular heterogeneity of diastolic spark activity. Remodeling in the area adjacent to MI differentially affects these RyR subpopulations. Reduction of the number of sparks near TTs and reduced local NCX removal limit cellular Ca(2+) loss and raise SR Ca(2+) content, but may promote Ca(2+) waves.
在大型哺乳动物的心室肌细胞中，并非所有的兰尼碱受体（RyR）簇都与 T 管（TTs）相关；这种比例在心肌梗死后（MI）细胞重塑时增加。
在 MI 前后，从 TT 接近程度的角度来描述 RyR 功能特性。
本研究从健康猪的左心室（CTRL）或 MI 附近的区域分离心肌细胞。在共聚焦线扫描成像（fluo-3）下进行全细胞膜片钳电压钳时，测量 Ca（2+）瞬变，并根据 TT 接近程度（早期 Ca（2+）释放部位，F>F（50）在 20 毫秒内）或缺乏（延迟部位）对 Ca（2+）瞬变进行分段。随后，将舒张期自发性 Ca（2+）释放事件、Ca（2+）火花（反映 RyR 活性和特性）分配到这两个类别。
在 CTRL 中，TT 附近的火花频率较高，但火花持续时间明显较短。Na（+）/Ca（2+）交换体（NCX）阻断选择性地延长 TT 附近的火花持续时间，而 Ca（2+）通道内的 Ca（2+）流入不会影响火花特性。在 MI 中，由于 SR Ca（2+）含量增加，总火花质量增加。超长火花（>47.6 毫秒）更频繁地出现。靠近 TT 的火花比例减少；主要在延迟部位增加频率。靠近 TT 的火花仅观察到持续时间增加；在 MI 中，NCX 在膜上的 Ca（2+）去除显著降低。
TT 接近程度调节 RyR 簇特性，导致舒张期火花活动的细胞内异质性。MI 附近区域的重塑以不同的方式影响这些 RyR 亚群。靠近 TT 的火花数量减少和局部 NCX 去除减少限制了细胞 Ca（2+）损失并提高了 SR Ca（2+）含量，但可能会促进 Ca（2+）波的形成。
