Krep H, Lefurgey A, Graves S W, Hockett D, Ingram P, Hollenberg N K
Department of Medicine, Harvard Medical School, Boston, Massachusetts, USA.
Am J Physiol. 1996 Aug;271(2 Pt 2):H514-20. doi: 10.1152/ajpheart.1996.271.2.H514.
The Na pump in vascular smooth muscle (VSM) is likely to influence not only intracellular Na content but also the content and distribution of other cations and anions measured by electron probe X-ray microanalysis (EPXMA). The hypothesis we tested was that EPXMA of pump-inhibited VSM would yield a characteristic cellular elemental profile, providing insight into the contribution of the Na pump to the intracellular milieu and an approach to identifying when VSM operates under the constraints of pump inhibition. We assessed the contractile state and elemental EPXMA profile of rabbit aorta that was either quiescent or contracted by serotonin (10(-6) M) or ouabain (10(-6) M). VSM cytoplasm showed the anticipated low Na (28 +/- 2 mM) and high K (182 +/- 5 mM) content. With ouabain, Na rose and K fell to reverse the Na-to-K ratio (0.15 +/- 0.01 vs. 6.6 +/- 0.3; P < 0.01). With serotonin, the ratio rose slightly (0.28 +/- 0.2; P < 0.05). Nuclei and mitochondria showed a similar pattern. CI showed a small increase (56 +/- 2 to 102 +/- 4 mM) with ouabain, a shift that could not be accounted for on the basis of charge redistribution to maintain neutrality because the change in Na and K were essentially offsetting. EPXMA measures total and not ionized Ca. If changes in cytoplasmic Ca occurred, they were too small to be measured by the imaging methods employed. The sustained, myogenic contractile response of VSM to Na pump inhibition shows a characteristic elemental profile that could prove useful in its identification. Direct measurement of membrane potential during the myogenic response to Na pump inhibition should have a high priority.
血管平滑肌（VSM）中的钠泵可能不仅会影响细胞内钠含量，还会影响通过电子探针X射线微量分析（EPXMA）测量的其他阳离子和阴离子的含量及分布。我们所验证的假设是，对受泵抑制的VSM进行EPXMA分析会产生一种特征性的细胞元素图谱，从而深入了解钠泵对细胞内环境的贡献，并提供一种方法来确定VSM何时在泵抑制的限制条件下运作。我们评估了兔主动脉的收缩状态和元素EPXMA图谱，该主动脉处于静息状态，或由血清素（10⁻⁶ M）或哇巴因（10⁻⁶ M）使其收缩。VSM细胞质显示出预期的低钠（28±2 mM）和高钾（182±5 mM）含量。使用哇巴因时，钠含量升高而钾含量下降，使钠钾比逆转（0.15±0.01对6.6±0.3；P<0.01）。使用血清素时，该比值略有升高（0.28±0.2；P<0.05）。细胞核和线粒体呈现出类似的模式。使用哇巴因时，氯离子略有增加（56±2至102±4 mM），这种变化无法基于电荷重新分布以维持电中性来解释，因为钠和钾的变化基本相互抵消。EPXMA测量的是总钙而非离子化钙。如果细胞质钙发生变化，其变化太小，无法通过所采用的成像方法测量。VSM对钠泵抑制的持续性肌源性收缩反应显示出一种特征性的元素图谱，这可能有助于对其进行识别。在对钠泵抑制的肌源性反应过程中直接测量膜电位应具有高度优先性。
