Evidence for an electrogenic Na+-HCO3- symport in rat cardiac myocytes
Evidence for an electrogenic Na+-HCO3- symport in rat cardiac myocytes
复制标题
DOI：
10.1111/j.1469-7793.1998.137bf.x
复制
发表时间：
1998-10-01
影响因子：
5.5
通讯作者：
Cingolani, HE
中科院分区：
文献类型：
--
作者：
Aiello, EA;Petroff, NGV;Cingolani, HE
1. 采用膜片钳穿孔全细胞构型和pH荧光指示剂SNARF测定离体大鼠心室肌细胞Na+- hco3 -共转运的电致性。在恒定的细胞外pH（pH(o)）下，从Hepes缓冲液切换到HCO3-缓冲液，使静息膜电位（RMP）超极化2.9 +/- 0.4 mV （n = 9, P < 0.05）。在HCO3-存在的情况下，阴离子阻滞剂可使RMP脱极化2.6 +/- 0.5 mV （n = 5, P < 0.05）。在没有细胞外Na+的情况下，没有观察到HCO3诱导的超极化。HCO3-存在时动作电位持续时间（APD(50)）比无HCO3-存在时缩短29.2 +/- 6.1% （n = 6, P < 0.05）。在8 s内，电压箝位斜坡在-130 ~ +30 mV范围内产生准稳态电流。在HCO3-存在下，观察到Na+依赖和Cl-独立稳态外向电流的新组分的发展。在4种不同水平的胞外Na+下，测定了Na+- hco3 -共输运电流（I-Na,I-Bic）的逆转电位（E-rev）。HCO3-: Na+的化学计量比为2:1。在标准的全细胞实验中也分离研究了I-Na、I-Bic。在这些条件下，I-Na，I-Bic在-96.4 +/- 1.9 mV （n = 5）时发生反转，这与通过Na+-HCO3-共转运体每Na+离子流入2个HCO3-离子相一致。在外部HCO3-存在下，用45 mM细胞外K+使膜电位（E-m）去极化10分钟后，检测到显著的细胞内碱化（0.09 +/- 0.03 pH单位；n = 5, P < 0.05）。当用阴离子阻断剂DIDS预处理肌细胞时，pH(i)没有变化（0.001）。+/- 0.024 pH单位，n = 5, n.s)，或暴露于无Na+溶液（0.003 +/- 0.037 pH单位，n = 6, n.s）。以上结果表明，心脏Na+- hco3 -共转运是电致性的，对大鼠心室细胞的RMP和APD有影响。
1. The perforated whole-cell configuration of patch clamp and the pH fluorescent indicator SNARF were used to determine the electrogenicity of the Na+-HCO3- cotransport in isolated rat ventricular myocytes.2. Switching from Hepes buffer to HCO3- buffer at constant extracellular pH (pH(o)) hyperpolarized the resting membrane potential (RMP) by 2.9 +/- 0.4 mV (n = 9, P < 0.05). In the presence of HCO3-, the anion blocker SITS depolarized RMP by 2.6 +/- 0.5 mV (n = 5, P < 0.05). No HCO3--induced hyperpolarization was observed in the absence of extracellular Na+. The duration of the action potential measured at 50% of repolarization time (APD(50)) was 29.2 +/- 6.1% shorter in the presence of HCO3- than in its absence (n = 6, P < .05).3. Quasi-steady-state currents were evoked by voltage-clamped ramps ranging from -130 to +30 mV, during 8 s. The development of a novel component of Na+-dependent and Cl--independent steady-state outward current was observed in the presence of HCO3-. The reversal potential (E-rev) of the Na+-HCO3- cotransport current (I-Na,I-Bic) was measured at four different levels of extracellular Na+. A HCO3-: Na+ ratio compatible with a stoichiometry of 2:1 was detected. I-Na,I-Bic was also studied in isolation in standard whole-cell experiments. Under these conditions, I-Na,I-Bic reversed at -96.4 +/- 1.9 mV (n = 5), being consistent with the influx of 2 HCO3- ions per Na+ ion through the Na+-HCO3- cotransporter.4. In the presence of external HCO3- after 10 min of depolarizing the membrane potential (E-m) with 45 mM extracellular K+, a significant intracellular alkalinization was detected (0.09 +/- 0.03 pH units; n = 5, P < 0.05). No changes in pH(i) were observed when the myocytes were pre-treated with the anion blocker DIDS (0.001. +/- 0.024 pH units, n = 5, n.s), or when exposed to Na+-free solutions (0.003 +/- 0.037 pH units; n = 6, n.s).5. The above results allow us to conclude that the cardiac Na+-HCO3- cotransport is electrogenic and has an influence on RMP and APD of rat ventricular cells.