Kinetics and stoichiometry of coupled Na efflux and Ca influx (Na/Ca exchange) in barnacle muscle cells.
Kinetics and stoichiometry of coupled Na efflux and Ca influx (Na/Ca exchange) in barnacle muscle cells.
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藤壶肌肉细胞中耦合的Na外排和Ca涌入（Na/Ca交换）的动力学和化学计量。
DOI：
10.1085/jgp.93.6.1219
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发表时间：
1989-06
影响因子：
3.8
通讯作者：
BLAUSTEIN, MP
中科院分区：
文献类型：
--
作者：
RASGADOFLORES, H;SANTIAGO, EM;BLAUSTEIN, MP
通过测量内部灌注的 ATP 燃料细胞中的 22Na+ 流出和 45Ca2+ 流入，研究了巨型藤壶肌细胞中耦合的 Na+ 退出/Ca2+ 进入（以 Ca2+ 流入模式运行的 Na/Ca 交换），其中 Na+ 泵被 0.1 mM 哇巴因中毒。内部游离 Ca2+，[Ca2+]i，由含有 8 mM EGTA 和不同量 Ca2+ 的 Ca-EGTA 缓冲系统控制。咖啡因和线粒体解偶联剂 (FCCP) 可抑制内部储存中的 Ca2+ 隔离。为了最大限度地提高 Ca2+ 流入模式 Na/Ca 交换的条件，并消除示踪剂 Na/Na 交换，标准 Na+ 海水 (NaSW) 中的所有外部 Na+ 均被 Tris 或 Li+（分别为 Tris-SW 或 LiSW）取代。在两种无 Na 溶液中，当 [Ca2+]i 增加到 10(-8) M 以上时，观察到外部 Ca2+ (Cao) 依赖性 Na+ 流出；该外流被 [Ca2+]i = 0.3 microM (LiSW) 至 0.7 microM (Tris-SW) 半最大激活。在 LiSW 中 [Ca2+]o = 2.0 mM，在 Tris-SW 中 [Ca2+]o = 7.2 mM，Cao 依赖性 Na+ 流出被半最大激活；在[Ca2+]o、[Ca2+]i 和[Na+]i 饱和时，最大（计算出的）Cao 依赖性Na+ 流出量约为75 pmol#cm2.s。这种外流受到外部 Na+ 和 La3+ 的抑制，IC50 分别约为 125 和 0.4 mM。 Tris-SW 中还观察到 Nai 依赖性 Ca2+ 流入。这种 Ca2+ 流入还需要 [Ca2+]i 大于 10(-8) M。内部 Ca2+ 激活来自 LiSW（示踪剂 Ca/Ca 交换）的 Nai 独立 Ca2+ 流入，但在 Tris-SW 中，几乎所有 Cai 激活的 Ca2+ 流入都是 Nai 依赖性的（Na/Ca 交换）。 [Na+]i = 30 mM 时观察到半最大激活。 Tris-SW 中内部 Ca2+ 激活了 Cao 依赖性 Na+ 流出和 Nai 依赖性 Ca2+ 流入，这一事实意味着这两种通量是耦合的；活化的（细胞内）Ca2+似乎不被交换器转运。最大（计算得出）Nai 依赖性 Ca2+ 流入量为 -25 pmol/cm2.s。在 6 至 106 mM 之间的各种 [Na+]i 下，Cao 依赖性 Na+ 流出与 Nai 依赖性 Ca2+ 流入之比为 2.8-3.2:1（平均值 = 3.1:1）；这直接表明Na/Ca交换的化学计量（偶联比）为3:1。这些对 Na/Ca 交换器耦合比和动力学的观察表明，在静息细胞中，由于 [Ca2+]i 较低，交换器的周转率较低；因此，静止状态下的大部分 Ca2+ 排出（大约 1 pmol/cm2.s）是由 ATP 驱动的 Ca2+ 泵介导的。（摘要截断为 400 字）
Coupled Na+ exit/Ca2+ entry (Na/Ca exchange operating in the Ca2+ influx mode) was studied in giant barnacle muscle cells by measuring 22Na+ efflux and 45Ca2+ influx in internally perfused, ATP-fueled cells in which the Na+ pump was poisoned by 0.1 mM ouabain. Internal free Ca2+, [Ca2+]i, was controlled with a Ca-EGTA buffering system containing 8 mM EGTA and varying amounts of Ca2+. Ca2+ sequestration in internal stores was inhibited with caffeine and a mitochondrial uncoupler (FCCP). To maximize conditions for Ca2+ influx mode Na/Ca exchange, and to eliminate tracer Na/Na exchange, all of the external Na+ in the standard Na+ sea water (NaSW) was replaced by Tris or Li+ (Tris-SW or LiSW, respectively). In both Na-free solutions an external Ca2+ (Cao)-dependent Na+ efflux was observed when [Ca2+]i was increased above 10(-8) M; this efflux was half-maximally activated by [Ca2+]i = 0.3 microM (LiSW) to 0.7 microM (Tris-SW). The Cao-dependent Na+ efflux was half-maximally activated by [Ca2+]o = 2.0 mM in LiSW and 7.2 mM in Tris-SW; at saturating [Ca2+]o, [Ca2+]i, and [Na+]i the maximal (calculated) Cao-dependent Na+ efflux was approximately 75 pmol#cm2.s. This efflux was inhibited by external Na+ and La3+ with IC50's of approximately 125 and 0.4 mM, respectively. A Nai-dependent Ca2+ influx was also observed in Tris-SW. This Ca2+ influx also required [Ca2+]i greater than 10(-8) M. Internal Ca2+ activated a Nai-independent Ca2+ influx from LiSW (tracer Ca/Ca exchange), but in Tris-SW virtually all of the Cai-activated Ca2+ influx was Nai-dependent (Na/Ca exchange). Half-maximal activation was observed with [Na+]i = 30 mM. The fact that internal Ca2+ activates both a Cao-dependent Na+ efflux and a Nai- dependent Ca2+ influx in Tris-SW implies that these two fluxes are coupled; the activating (intracellular) Ca2+ does not appear to be transported by the exchanger. The maximal (calculated) Nai-dependent Ca2+ influx was -25 pmol/cm2.s. At various [Na+]i between 6 and 106 mM, the ratio of the Cao-dependent Na+ efflux to the Nai-dependent Ca2+ influx was 2.8-3.2:1 (mean = 3.1:1); this directly demonstrates that the stoichiometry (coupling ratio) of the Na/Ca exchange is 3:1. These observations on the coupling ratio and kinetics of the Na/Ca exchanger imply that in resting cells the exchanger turns over at a low rate because of the low [Ca2+]i; much of the Ca2+ extrusion at rest (approximately 1 pmol/cm2.s) is thus mediated by an ATP-driven Ca2+ pump.(ABSTRACT TRUNCATED AT 400 WORDS)
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影响因子：
5.5
作者：
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