Baartscheer A, Schumacher C A, van Borren M M G J, Belterman C N W, Coronel R, Fiolet J W T
Experimental and Molecular Cardiology Group, Laboratory of Experimental Cardiology, Room M-0-052, Academic Medical Center, University of Amsterdam, P.O. Box 22700, 1100 DE, Amsterdam, The Netherlands.
Cardiovasc Res. 2003 Mar 15;57(4):1015-24. doi: 10.1016/s0008-6363(02)00809-x.
Cytosolic sodium ([Na+]i) is increased in heart failure (HF). We hypothesize that up-regulation of Na+/H+-exchanger (NHE) in heart failure is causal to the increase of [Na+]i and underlies disturbance of cytosolic calcium ([Ca2+]i) handling.
Heart failure was induced in rabbits by combined volume and pressure overload. Age-matched animals served as control. [Na+]i, cytosolic calcium [Ca2+]i and cytosolic pH (pH(i)) were measured in isolated left ventricular midmural myocytes with SBFI, indo-1 and SNARF. SR calcium content was measured as the response of [Ca2+]i to rapid cooling (RC). Calcium after-transients were elicited by cessation of rapid stimulation (3 Hz) in the presence of 100 nmol/l noradrenalin. NHE and Na+/K+-ATPase activity were inhibited with 10 micromol/l cariporide and 100 micromol/l ouabain, respectively.
At all stimulation rates (0-3 Hz) [Na+]i and diastolic [Ca2+]i were significantly higher in HF than in control. With increasing frequency [Na+]i and diastolic [Ca2+]i progressively increased in HF and control, and the calcium transient amplitude (measured as total calcium released from SR) decreased in HF and increased in control. In HF (at 2 Hz), SR calcium content was reduced by 40% and the calcium gradient across the SR membrane by 60%. Fractional systolic SR calcium release was 90% in HF and 60% in control. In HF the rate of pH(i) recovery following acid loading was much faster at all pH(i) and NHE dependent sodium influx was almost twice as high as in control. In HF cariporide (10 micromol/l, 5 min) reduced [Na+]i and end diastolic [Ca2+]i to almost control values, and reversed the relation between calcium transient amplitude and stimulation rate from negative to positive. It increased SR calcium content and SR membrane gradient and decreased fractional systolic SR depletion to 60%. Cariporide greatly reduced the susceptibility to develop calcium after-transients. In control animals, cariporide had only minor effects on all these parameters. Increase of [Na+]i with ouabain in control myocytes induced abnormal calcium handling as found in HF.
In HF up-regulation of NHE activity is causal to increased [Na+]i and secondarily to disturbed diastolic, systolic and SR calcium handling. Specific inhibition of NHE partly normalized [Na+]i, end diastolic [Ca2+]i, and SR calcium handling and reduced the incidence of calcium after-transients. Chronic treatment with specific NHE inhibitors may provide a useful future therapeutic option in treatment of developing hypertrophy and heart failure.
心力衰竭（HF）时细胞溶质钠（[Na⁺]i）升高。我们假设心力衰竭时钠/氢交换体（NHE）上调是[Na⁺]i升高的原因，并且是细胞溶质钙（[Ca²⁺]i）处理紊乱的基础。
通过容量和压力超负荷联合诱导家兔发生心力衰竭。年龄匹配的动物作为对照。用SBFI、indo-1和SNARF在分离的左心室中层心肌细胞中测量[Na⁺]i、细胞溶质钙[Ca²⁺]i和细胞溶质pH（pH(i)）。通过[Ca²⁺]i对快速冷却（RC）的反应测量肌浆网钙含量。在100 nmol/L去甲肾上腺素存在下，通过停止快速刺激（3 Hz）引发钙后除极。分别用10 μmol/L卡立泊来德和100 μmol/L哇巴因抑制NHE和钠/钾-ATP酶活性。
在所有刺激频率（0 - 3 Hz）下，HF组的[Na⁺]i和舒张期[Ca²⁺]i均显著高于对照组。随着频率增加，HF组和对照组的[Na⁺]i和舒张期[Ca²⁺]i逐渐升高，HF组的钙瞬变幅度（以从肌浆网释放的总钙量测量）降低，而对照组升高。在HF组（2 Hz时），肌浆网钙含量降低40%，肌浆网膜上的钙梯度降低60%。HF组收缩期肌浆网钙释放分数为90%，对照组为60%。在HF组，所有pH(i)下酸负荷后pH(i)恢复速率都快得多，且NHE依赖性钠内流几乎是对照组的两倍。在HF组，卡立泊来德（10 μmol/L，5分钟）将[Na⁺]i和舒张末期[Ca²⁺]i降低至几乎对照值，并使钙瞬变幅度与刺激频率之间的关系从负变正。它增加了肌浆网钙含量和肌浆网膜梯度，并将收缩期肌浆网钙耗竭分数降低至60%。卡立泊来德大大降低了发生钙后除极的易感性。在对照动物中，卡立泊来德对所有这些参数仅有轻微影响。对照组心肌细胞中用哇巴因使[Na⁺]i升高诱导出如在HF组中所见的异常钙处理。
在HF中，NHE活性上调是[Na⁺]i升高的原因，继而导致舒张期、收缩期和肌浆网钙处理紊乱。特异性抑制NHE可部分使[Na⁺]i、舒张末期[Ca²⁺]i和肌浆网钙处理正常化，并降低钙后除极的发生率。用特异性NHE抑制剂进行长期治疗可能为治疗进展性肥大和心力衰竭提供一种有用的未来治疗选择。
