Baartscheer Antonius, Schumacher Cees A, Coronel Ruben, Fiolet Jan W T
Experimental Cardiology, Heart Failure Research Center, Academic Medical Center, University of Amsterdam Amsterdam, Netherlands.
Front Physiol. 2011 Mar 11;2:10. doi: 10.3389/fphys.2011.00010. eCollection 2011.
Metabolic inhibition causes a decline in mechanical performance and, if prolonged, myocardial contracture and cell death. The decline in mechanical performance is mainly due to altered intracellular calcium handling, which is under control of the Na(+)/Ca(2+)-exchanger (NCX) The driving force of the NCX (ΔG(ncx)) determines the activity of NCX. The aim of this study was to describe the relation between ΔG(ncx) and calcium homeostasis during metabolic inhibition.
In left ventricular rabbit myocytes, during metabolic inhibition (2 mmol/L sodium cyanide), sodium (Na(+)), calcium (Ca(2+);), and action potentials were determined with SBFI, indo-1, and the patch clamp technique. Changes of ΔG(ncx) were calculated.
During metabolic inhibition: The first 8 min Na(+) remained constant, systolic calcium decreased from 532 ± 28 to 82 ± 13 nM, diastolic calcium decreased from 121 ± 12 to 36 ± 10 nM and the sarcoplasmic reticulum (SR) calcium content was depleted for 85 ± 3%. After 8 min Na(+); and diastolic calcium started to increase to 30 ± 1.3 mmol/L and 500 ± 31 nM after 30 min respectively. The action potential duration shortened biphasically. In the first 5 min it shortened from 225 ± 12 to 153 ± 11 ms and remained almost constant until it shortened again after 10 min. After 14 min action potential and calcium transients disappeared due to unexcitability of the myocytes. This resulted in an increased of the time average of ΔG(ncx) from 6.2 ± 0.2 to 7.7 ± 0.3 kJ/mol during the first 3 min, where after it decreased and became negative after about 15 min.
Metabolic inhibition caused an early increase of ΔG(ncx) caused by shortening of the action potential. The increase of ΔG(ncx) contributed to decrease of diastolic calcium, calcium transient amplitude, SR calcium content, and contractility. The increase of diastolic calcium started after ΔG(ncx) became lower than under aerobic conditions.
代谢抑制会导致机械性能下降，若持续时间过长，则会引发心肌挛缩和细胞死亡。机械性能下降主要是由于细胞内钙处理的改变，而这受钠/钙交换体（NCX）的调控。NCX的驱动力（ΔG(ncx)）决定了NCX的活性。本研究的目的是描述代谢抑制期间ΔG(ncx)与钙稳态之间的关系。
在兔左心室肌细胞中，于代谢抑制（2 mmol/L氰化钠）期间，采用SBFI、indo-1和膜片钳技术测定钠（Na⁺）、钙（Ca²⁺）及动作电位。计算ΔG(ncx)的变化。
在代谢抑制期间：最初8分钟，Na⁺保持恒定，收缩期钙从532±28 nM降至82±13 nM，舒张期钙从121±12 nM降至36±10 nM，肌浆网（SR）钙含量减少85±3%。8分钟后，Na⁺和舒张期钙分别在30分钟后开始增加至30±1.3 mmol/L和500±31 nM。动作电位时程呈双相缩短。最初5分钟内，其从225±12 ms缩短至153±11 ms，并几乎保持恒定，直至10分钟后再次缩短。14分钟后，由于心肌细胞失去兴奋性，动作电位和钙瞬变消失。这导致在最初3分钟内，ΔG(ncx)的时间平均值从6.2±0.2 kJ/mol增加至7.7±0.3 kJ/mol，此后其下降，并在约15分钟后变为负值。
代谢抑制导致动作电位缩短，进而引起早期ΔG(ncx)升高。ΔG(ncx)的升高导致舒张期钙、钙瞬变幅度、SR钙含量和收缩性降低。舒张期钙的升高在ΔG(ncx)低于有氧条件下时开始出现。
