Steady-state and dynamic properties of cardiac sodium-calcium exchange. Ion and voltage dependencies of the transport cycle.
Steady-state and dynamic properties of cardiac sodium-calcium exchange. Ion and voltage dependencies of the transport cycle.
复制标题
心脏钠钙交换的稳态和动态特性。运输周期的离子和电压依赖性。
DOI：
10.1085/jgp.100.6.963
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发表时间：
1992-12
期刊：
影响因子：
--
通讯作者：
Hilgemann DW
中科院分区：
文献类型：
--
作者：
Matsuoka S;Hilgemann DW
在用胰凝乳蛋白酶解除交换器调节后，在豚鼠心室细胞的巨型膜片中研究了钠钙交换电流的离子和电压依赖性。 （a）在零反式条件下，随着细胞外钠（Nao）浓度的降低，用于激活隔离内向交换电流的细胞质钙（Cai）的半最大浓度（Kh）降低。随着细胞外钙 (Cao) 浓度的降低，用于激活隔离外向交换电流的细胞质钠 (Nai) 的 Kh 值也随之降低。 (b) 外向交换电流与 Nai 和 Cao 饱和浓度的电流-电压 (I-V) 关系具有较浅的斜率（大约 100 mV 的两倍变化），并且在非常正的电位下有轻微的饱和趋势。随着 Nai 浓度的降低，外向电流变得陡峭，使得 Nai 的 Kh 随着去极化而降低。玻尔兹曼方程 (e alpha.Em/26.6) 很好地描述了 Nai 随去极化而减少的 Kh 值，斜率 (alpha) 为 -0.06。 (c) 随着曹浓度降低，外向电流的电压依赖性消失，并且曹的 Kh 在去极化时增加，玻尔兹曼斜率为 0.26。 (d) 在零反式条件下，内向交换电流的 I-V 关系也几乎是线性的（大约 100 mV 的两倍变化），并且随着 Cai 浓度的降低，显示出一些超极化的饱和趋势。 Cai 的 Kh 随着去极化而降低（玻尔兹曼斜率，-0.10）。在高 (300 mM) Nao 浓度存在下，内向电流的电压依赖性降低。 (e) 在膜两侧同时存在 Na 和 Ca 的情况下，与饱和 Nai 的 I-V 关系显示出 S 形形状，并且在正电位下具有明显的饱和度。测得的逆转电势接近 3 Na 至 1 Ca 交换的预期平衡电势。 (f) Nai 和 Cai 在外向电流方面存在竞争性相互作用，但在内向电流方面则以竞争-非竞争混合方式相互作用。 (g) 蔡以电压依赖的方式抑制向外的交换电流。 Cai 的半有效抑制浓度 (Ki) 在去极化后增加，玻尔兹曼斜率在 25 mM Nai 中为 0.32，在 100 mM Nai 中为 0.20。 (h) Nai 还依赖于电压抑制了内向交换电流。 Ki 在去极化时下降（玻尔兹曼斜率，3 microM Cai 时为 -0.11，1.08 mM Cai 时为 -0.10）。（摘要截断为 400 字）
Ion and voltage dependencies of sodium-calcium exchange current were studied in giant membrane patches from guinea pig ventricular cells after deregulation of the exchanger with chymotrypsin. (a) Under zero- trans conditions, the half-maximum concentration (Kh) of cytoplasmic calcium (Cai) for activation of the isolated inward exchange current decreased as the extracellular sodium (Nao) concentration was decreased. The Kh of cytoplasmic sodium (Nai) for activation of the isolated outward exchange current decreased as the extracellular calcium (Cao) concentration was decreased. (b) The current-voltage (I- V) relation of the outward exchange current with saturating concentrations of Nai and Cao had a shallow slope (twofold change in approximately 100 mV) and a slight saturation tendency at very positive potentials. The outward current gained in steepness as the Nai concentration was decreased, such that the Kh for Nai decreased with depolarization. The decrease of Kh for Nai with depolarization was well described by a Boltzmann equation (e alpha.Em/26.6) with a slope (alpha) of -0.06. (c) Voltage dependence of the outward current was lost as the Cao concentration was decreased, and the Kh for Cao increased upon depolarization with a Boltzmann slope of 0.26. (d) The I- V relation of the inward exchange current, under zero-trans conditions, was also almost linear (twofold change in approximately 100 mV) and showed some saturation tendency with hyperpolarization as the Cai concentration was decreased. The Kh for Cai decreased with depolarization (Boltzmann slope, -0.10). Voltage dependence of the inward current was decreased in the presence of a high (300 mM) Nao concentration. (e) In the presence of both Na and Ca on both membrane sides, the I-V relations with saturating Nai show sigmoidal shape and clear saturation at positive potentials. Measured reversal potentials were close to the equilibrium potential expected for a 3 Na to 1 Ca exchange. (f) Nai and Cai interacted competitively with respect to the outward current, but in a mixed competitive-noncompetitive fashion with respect to the inward current. (g) Cai inhibited the outward exchange current in a voltage-dependent manner. The half-effective concentration for inhibition (Ki) by Cai increased upon depolarization with a Boltzmann slope of 0.32 in 25 mM Nai and 0.20 in 100 mM Nai. (h) Nai also inhibited the inward exchange current voltage dependently. The Ki decreased upon depolarization (Boltzmann slope, -0.11 at 3 microM Cai and -0.10 at 1.08 mM Cai).(ABSTRACT TRUNCATED AT 400 WORDS)