Functional diversity of electrogenic Na+-HCO3- cotransport in ventricular myocytes from rat, rabbit and guinea pig
Functional diversity of electrogenic Na+-HCO3- cotransport in ventricular myocytes from rat, rabbit and guinea pig
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DOI：
10.1113/jphysiol.2004.071068
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发表时间：
2005-01-15
影响因子：
5.5
通讯作者：
Spitzer, KL
中科院分区：
文献类型：
--
作者：
Yamamoto, T;Swietach, P;Spitzer, KL
Na+-HCO3-协同转运蛋白（NBC）是心肌中重要的肌膜酸挤出机。心脏中功能性表达的 NBC 特征存在争议，有报道表明转运蛋白为电中性（NBCn；1HCO(3)(-)：1Na(+)；耦合系数 N = 1）或产电形式（NBCe；相当于 2HCO(3)(-)：1Na(+)；N = 2）。我们使用电压钳和落射荧光技术来比较兔、大鼠和豚鼠离体心室肌细胞的 NBC 活性。去极化（通过电压钳或高钾血症）可逆地增加稳态 pH(i)，而超极化则降低它，这种效应仅在 CO2/HCO3 缓冲溶液中可见，并被 S0859（心脏 NBC 抑制剂）阻断。这些 pHi 变化幅度的物种差异为大鼠 > 豚鼠，近似于兔子。强直去极化（- 140 mV 至 - 0 mV）加速了 NBC 介导的 pH(i) 从细胞内酸负荷的恢复。在 0 mV 时，静息 pHi 下 NBC 介导的外向电流为 +0.52 +/- 0.05 pA pF(-1)（大鼠，n = 5）、+0.26 +/- 0.05 pA pF(-1)（豚鼠，n = 5）和 +0.10 +/- 0.03 pA pF(-1)（兔子，n = 9），反转电位接近-100 mV，与 N = 2 一致。上述结果表明这些物种中具有功能活性的电压敏感 NBCe。然而，对 NBCe 的逆转电位负的电压钳超极化未能终止或逆转 NBC 介导的 pH(i) 从酸负荷的恢复，尽管其速度显着减慢，这表明电中性 NBC 也可能是可操作的。 NBC 介导的 pH(i) 恢复与 [Na+](i) 的升高相关，其速率类似于通过 NHE 介导的 25%，并且与 N = 1 和 N = 2 之间的表观 NBC 化学计量一致。 总之，心室肌细胞中的 NBCe 在所测试的三个物种中表现出相当大的功能差异（大鼠中最大，兔子中最小），并且可能与某些 NBCn 活性共存。
The Na+-HCO3- cotransporter (NBC) is an important sarcolemmal acid extruder in cardiac muscle. The characteristics of NBC expressed functionally in heart are controversial, with reports suggesting electroneutral (NBCn; 1HCO(3)(-) : 1Na(+); coupling coefficient N = 1) or electrogenic forms of the transporter (NBCe; equivalent to 2HCO(3)(-) : 1Na(+); N = 2). We have used voltage-clamp and epifluorescence techniques to compare NBC activity in isolated ventricular myocytes from rabbit, rat and guinea pig. Depolarization (by voltage clamp or hyperkalaemia) reversibly increased steady-state pH(i) while hyperpolarization decreased it, effects seen only in CO2/HCO3--buffered solutions, and blocked by S0859 (cardiac NBC inhibitor). Species differences in amplitude of these pHi changes were rat > guinea pig approximate to rabbit. Tonic depolarization (- 140 mV to - 0 mV) accelerated NBC-mediated pH(i) recovery from an intracellular acid load. At 0 mV, NBC-mediated outward current at resting pHi was +0.52 +/- 0.05 pA pF(-1) (rat, n = 5), +0.26 +/- 0.05 pA pF(-1) (guinea pig, n = 5) and +0.10 +/- 0.03 pA pF(-1) (rabbit, n = 9), with reversal potentials near -100 mV, consistent with N = 2. The above results indicate a functionally active voltage-sensitive NBCe in these species. Voltage-clamp hyperpolarization negative to the reversal potential for NBCe failed, however, to terminate or reverse NBC-mediated pH(i)-recovery from an acid load although it was slowed significantly, suggesting electroneutral NBC may also be operational. NBC-mediated pH(i) recovery was associated with a rise of [Na+](i) at a rate similar to25% of that mediated via NHE, and consistent with an apparent NBC stoichiometry between N = 1 and N = 2. In conclusion, NBCe in the ventricular myocyte displays considerable functional variation among the three species tested (greatest in rat, least in rabbit) and may coexist with some NBCn activity.