Kirk Malcolm M, Izu Leighton T, Chen-Izu Ye, McCulle Stacey L, Wier W Gil, Balke C William, Shorofsky Stephen R
Department of Medicine, University of Maryland School of Medicine, Baltimore, MD 21201-1541, USA.
J Physiol. 2003 Mar 1;547(Pt 2):441-51. doi: 10.1113/jphysiol.2002.034355. Epub 2003 Jan 31.
Cardiac atrial cells lack a regular system of transverse tubules like that in cardiac ventricular cells. Nevertheless, many atrial cells do possess an irregular internal transverse-axial tubular system (TATS). To investigate the possible role of the TATS in excitation-contraction coupling in atrial myocytes, we visualized the TATS (labelled with the fluorescent indicator, Di-8-ANEPPS) simultaneously with Ca2+ transients and/or Ca2+ sparks (fluo-4). In confocal transverse linescan images of field-stimulated cells, whole-cell Ca2+ transients had two morphologies: 'U-shaped' transients and irregular or 'W-shaped' transients with a varying number of points of origin of the Ca2+ transient. About half (54 %, n =289 cells, 13 animals) of the cells had a TATS. Cells with TATS had a larger mean diameter (13.2 +/- 2.8 microm) than cells without TATS (11.7 +/- 2.0 microm) and were more common in the left atrium (n = 206 cells; left atrium: 76 with TATS, 30 without TATS; right atrium: 42 with TATS, 58 without TATS). Simultaneous measurement of Ca2+ sparks and sarcolemmal structures showed that cells without TATS had U-shaped transients that started at the cell periphery, and cells with TATS had W-shaped transients that began simultaneously at the cell periphery and the TATS. Most (82 out of 102 from 31 cells) 'spontaneous' (non-depolarized) Ca2+ sparks occurred within 1 microm of a sarcolemmal structure (cell periphery or TATS), and 33 % occurred within 1 pixel (0.125 microm). We conclude that the presence of a sarcolemmal membrane either at the cell periphery or in the TATS in close apposition to the sarcoplasmic reticulum is required for the initiation of an evoked Ca2+ transient and for spontaneous Ca2+ sparks.
心房细胞缺乏像心室细胞那样规则的横管系统。然而，许多心房细胞确实拥有一个不规则的内部横向 - 轴向管状系统（TATS）。为了研究TATS在心房肌细胞兴奋 - 收缩偶联中的可能作用，我们使用荧光指示剂Di - 8 - ANEPPS标记TATS，同时观察Ca²⁺瞬变和/或Ca²⁺火花（fluo - 4）。在电场刺激细胞的共聚焦横向线扫描图像中，全细胞Ca²⁺瞬变有两种形态：“U形”瞬变和不规则或“W形”瞬变，Ca²⁺瞬变的起源点数量各不相同。约一半（54%，n = 289个细胞，13只动物）的细胞有TATS。有TATS的细胞平均直径（13.2±2.8微米）比没有TATS的细胞（11.7±2.0微米）大，并且在左心房更常见（n = 206个细胞；左心房：有TATS的76个，没有TATS的30个；右心房：有TATS的42个，没有TATS的58个）。Ca²⁺火花和肌膜结构的同步测量表明，没有TATS的细胞具有从细胞周边开始的U形瞬变，有TATS的细胞具有在细胞周边和TATS同时开始的W形瞬变。大多数（来自31个细胞的102个中的82个）“自发”（非去极化）Ca²⁺火花发生在距离肌膜结构（细胞周边或TATS）1微米内，33%发生在1像素（0.125微米）内。我们得出结论，诱发的Ca²⁺瞬变的起始以及自发的Ca²⁺火花需要在细胞周边或与肌浆网紧密相邻的TATS处存在肌膜。
