Somlyo A P, Somlyo A V, Shuman H
J Cell Biol. 1979 May;81(2):316-35. doi: 10.1083/jcb.81.2.316.
Electron probe analysis of dry cryosections was used to determine the composition of the cytoplasm and organelles of rabbit portal-anterior mesenteric vein (PAMV) smooth muscle. All analytical values given are in mmol/kg wt +/- SEM. Cytoplasmic concentrations in normal, resting muscles were: K, 611 +/- 1.7; Na, 167 +/- 2.7; Cl, 278 +/- 1.0; Mg, 36 +/- 1.1; Ca, 1.9 +/- 0.5; and P, 247 +/- 1.1. Hence, the sum of intracellular Na + K exceeded cytoplasmic Cl by 500 mmol/kg dry wt, while the calculated total, nondiffusible solute was approximately 50 mmol/kg. Cytoplasmic K and Cl were increased in smooth muscles incubated in solutions containing an excess (80 mM) of KCl. Nuclear and cytoplasmic Na and Ca concentrations were not significantly different. The mitochondrial Ca content in normal fibers was low, 0.8 +/- 0.5, and there was no evidence of mitochondrial Ca sequestration in muscles frozen after a K contracture lasint 30 min. Transmitochondrial gradients of K, Na, and Cl were small (0.9--1.2). In damaged fibers, massive mitochondrial Ca accumulation of up to 2 mol/kg dry wt in granule form and associated with P could be demonstrated. Our findings suggest (a) that the nonDonnan distribution of Cl in smooth muscle is not caused by sequestration in organelles, and that considerations of osmotic equilibrium and electroneutrality suggest the existence of unidentified nondiffusible anions in smooth muscle, (b) that nuclei do not contain concentrations of Na or Ca in excess of cytoplasmic levels, (c) that mitochondria in PAMV smooth muscle do not play a major role in regulating cytoplasmic Ca during physiological levels of contraction but can be massively Ca loaded in damaged cells, and (d) that the in situ transmitochondrial gradients of K, Na, and Cl do not show these ions to be distributed according to a large electromotive Donnan force.
采用电子探针分析干冻切片来测定兔门静脉-肠系膜前静脉（PAMV）平滑肌细胞质和细胞器的组成。给出的所有分析值均以mmol/kg湿重±标准误表示。正常静息肌肉中的细胞质浓度为：钾，611±1.7；钠，167±2.7；氯，278±1.0；镁，36±1.1；钙，1.9±0.5；磷，247±1.1。因此，细胞内钠+钾的总和比细胞质氯高出500 mmol/kg干重，而计算得出的总非扩散性溶质约为50 mmol/kg。在含过量（80 mM）氯化钾的溶液中孵育的平滑肌中，细胞质钾和氯增加。细胞核和细胞质中的钠和钙浓度无显著差异。正常纤维中的线粒体钙含量较低，为0.8±0.5，并且在钾收缩30分钟后冷冻的肌肉中没有线粒体钙螯合的证据。钾、钠和氯的跨线粒体梯度较小（0.9 - 1.2）。在受损纤维中，可以证明线粒体大量积累钙，以颗粒形式存在，高达2 mol/kg干重，且与磷有关。我们的研究结果表明：（a）平滑肌中氯的非唐南分布不是由细胞器中的螯合作用引起的，并且渗透压平衡和电中性的考虑表明平滑肌中存在未确定的非扩散性阴离子；（b）细胞核中的钠或钙浓度不超过细胞质水平；（c）PAMV平滑肌中的线粒体在生理收缩水平期间在调节细胞质钙方面不发挥主要作用，但在受损细胞中可大量加载钙；（d）原位钾、钠和氯的跨线粒体梯度并未显示这些离子根据大的电动唐南力进行分布。
