Pappone P A, Lee S C
Section of Neurobiology, Physiology and Behavior, University of California, Davis 95616, USA.
J Gen Physiol. 1996 Nov;108(5):393-404. doi: 10.1085/jgp.108.5.393.
Stimulation of brown adipocytes by their sympathetic innervation plays a major role in body energy homeostasis by regulating the energy-wasting activity of the tissue. The norepinephrine released by sympathetic activity acts on adrenergic receptors to activate a variety of metabolic and membrane responses. Since sympathetic stimulation may also release vesicular ATP, we tested brown fat cells for ATP responses. We find that micromolar concentrations of extracellular ATP initiates profound changes in the membrane trafficking of brown adipocytes. ATP elicited substantial increases in total cell membrane capacitance, averaging approximately 30% over basal levels and occurring on a time scale of seconds to minutes. The membrane capacitance increase showed an agonist sensitivity of 2-methylthio-ATP > or = ATP > ADP > > adenosine, consistent with mediation by a P2r type purinergic receptor. Membrane capacitance increases were not seen when cytosolic calcium was increased by adrenergic stimulation, and capacitance responses to ATP were similar in the presence and absence of extracellular calcium. These results indicate that increases in cytosolic calcium alone do not mediate the membrane response to ATP. Photometric assessment of surface-accessible membrane using the dye FM1-43 showed that ATP caused an approximate doubling of the amount of membrane actively trafficking with the cell surface. The discrepancy in the magnitudes of the capacitance and fluorescence changes suggests that ATP both activates exocytosis and alters other aspects of membrane handling. These findings suggest that secretion, mobilization of membrane transporters, and/or surface membrane expression of receptors may be regulated in brown adipocytes by P2r purinergic receptor activity.
棕色脂肪细胞的交感神经支配刺激通过调节该组织的能量消耗活动，在机体能量稳态中发挥着重要作用。交感神经活动释放的去甲肾上腺素作用于肾上腺素能受体，激活各种代谢和膜反应。由于交感神经刺激也可能释放囊泡ATP，我们测试了棕色脂肪细胞对ATP的反应。我们发现，微摩尔浓度的细胞外ATP会引发棕色脂肪细胞膜转运的深刻变化。ATP使总细胞膜电容大幅增加，平均比基础水平高出约30%，且在数秒至数分钟的时间尺度上发生。膜电容增加表现出对激动剂的敏感性为2-甲硫基-ATP≥ATP＞ADP＞＞腺苷，这与P2r型嘌呤能受体介导一致。当通过肾上腺素能刺激增加胞质钙时，未观察到膜电容增加，并且在存在和不存在细胞外钙的情况下，对ATP的电容反应相似。这些结果表明，仅胞质钙增加并不能介导对ATP的膜反应。使用染料FM1-43对表面可及膜进行光度评估表明，ATP使与细胞表面积极转运的膜量增加了约一倍。电容和荧光变化幅度的差异表明，ATP既能激活胞吐作用，又能改变膜处理的其他方面。这些发现表明，棕色脂肪细胞中的分泌、膜转运体的动员和/或受体的表面膜表达可能受P2r嘌呤能受体活性调节。
