Introduction: The Prospects for Education: Individualization, Globalization, and Social Change
Introduction: The Prospects for Education: Individualization, Globalization, and Social Change
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简介：教育的前景：个性化、全球化和社会变革
DOI：
10.1016/s0021-9258(19)70021-0
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
A. Halsey
中科院分区：
文献类型：
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作者：
H. Lauder;P. Brown;J. Dillabough;A. Halsey
在人工产生的pH梯度和膜电位存在和不存在的情况下，研究了兔骨骼肌肌浆网囊泡对atp依赖性Ca2+的摄取。H+和K+扩散电位通过肌浆网的H+和K、Na通道产生，由小泡从低pH到高pH或从高K+到低K+的转移。膜电位测量使用电压敏感荧光染料3,3 ' -二戊基-2,2 ' -草碳菁。发现Ca2+摄取的初始速率在pH梯度和膜电位（内部为负）的存在下增加。反过来，在Ca2+运输过程中，K+-或H+-诱导的膜电位衰减速度加快，这表明活跃的Ca2+摄取刺激了K+和H+从囊泡中释放。K+（或H+）释放与Ca2+运输的比值接近2。Ca2+- atp酶并没有直接催化K+的释放。反对直接偶联atp介导的2k +-Ca2+或K+-Ca2+交换反应的证据是：(i)当K+被Na+或可以通过K+，Na+渗透性囊泡通道快速渗透的有机阳离子取代时，获得类似的结果；（ii） Ca2+运输不会导致从K+，Na+不渗透性囊泡中释放86Rb+或22Na+。这些研究支持肌浆网的电致Ca2+运输系统。结果进一步表明，在Ca2+运输过程中，膜电位（内部正）的发展可能被渗透的阳离子K+， Na+和H+的反向运动抵消。
ATP-dependent Ca2+ uptake by rabbit skeletal muscle sarcoplasmic reticulum vesicles has been studied in the presence and absence of artificially generated pH gradients and membrane potentials. H+ and K+ diffusion potentials were generated via the H+ and K,Na channels of sarcoplasmic reticulum by transfer of vesicles from low to high pH, or from high to low K+. Membrane potentials were measured using the voltage-sensitive fluorescent dye 3,3‘-dipentyl-2,2‘-oxacarbocyanine. The initial rate of Ca2+ uptake was found to be increased in the presence of a pH gradient and membrane potential (negative inside). In turn, the rates of decay of K+- or H+-induced membrane potentials were accelerated during Ca2+ transport, suggesting that active Ca2+ uptake stimulated the release of K+ and H+ from the vesicles. The ratio of K+ (or H+) release to Ca2+ transport was near two. Release of K+ did not appear to be directly catalyzed by the Ca2+-ATPase. Evidence against a directly coupled ATP-mediated 2 K+-Ca2+ or K+-Ca2+ exchange reaction was that (i) similar results were obtained when K+ was substituted by Na+ or by organic cations which could rapidly permeate through the channel of K+,Na+-permeable vesicles and (ii) Ca2+ transport did not result in an equivalent release of 86Rb+ or 22Na+ from K+,Na+-impermeable vesicles. These studies are in support of an electrogenic Ca2+ transport system in sarcoplasmic reticulum. The results further suggest that during Ca2+ transport development of a membrane potential (positive inside) is likely nullified by the countermovement of the permeant cations K+, Na+, and H+.