Unit of Cardiac Physiology, Division of Cardiovascular Sciences, Manchester Academic Health Sciences Centre, University of Manchester, Manchester, UK.
Biomedical Research Centre, School of Environment and Life Sciences, Peel Building, University of Salford, Salford, UK.
J Physiol. 2017 Aug 15;595(16):5545-5555. doi: 10.1113/JP274366. Epub 2017 Jul 23.
For the heart to function as a pump, intracellular calcium concentration ([Ca ] ) must increase during systole to activate contraction and then fall, during diastole, to allow the myofilaments to relax and the heart to refill with blood. The present study investigates the control of diastolic [Ca ] in rat ventricular myocytes. We show that diastolic [Ca ] is increased by manoeuvres that decrease sarcoplasmic reticulum function. This is accompanied by a decrease of systolic [Ca ] such that the time-averaged [Ca ] remains constant. We report that diastolic [Ca ] is controlled by the balance between Ca entry and Ca efflux during systole. The results of the present study identify a novel mechanism by which changes of the amplitude of the systolic Ca transient control diastolic [Ca ] .
The intracellular Ca concentration ([Ca ] ) must be sufficently low in diastole so that the ventricle is relaxed and can refill with blood. Interference with this will impair relaxation. The factors responsible for regulation of diastolic [Ca ] , in particular the relative roles of the sarcoplasmic reticulum (SR) and surface membrane, are unclear. We investigated the effects on diastolic [Ca ] that result from the changes of Ca cycling known to occur in heart failure. Experiments were performed using Fluo-3 in voltage clamped rat ventricular myocytes. Increasing stimulation frequency increased diastolic [Ca ] . This increase of [Ca ] was larger when SR function was impaired either by making the ryanodine receptor leaky (with caffeine or ryanodine) or by decreasing sarco/endoplasmic reticulum Ca-ATPase activity with thapsigargin. The increase of diastolic [Ca ] produced by interfering with the SR was accompanied by a decrease of the amplitude of the systolic Ca transient, such that there was no change of time-averaged [Ca ] . Time-averaged [Ca ] was increased by β-adrenergic stimulation with isoprenaline and increased in a saturating manner with increased stimulation frequency; average [Ca ] was a linear function of Ca entry per unit time. Diastolic and time-averaged [Ca ] were decreased by decreasing the L-type Ca current (with 50 μm cadmium chloride). We conclude that diastolic [Ca ] is controlled by the balance between Ca entry and efflux during systole. Furthermore, manoeuvres that decrease the amplitude of the Ca transient (without decreasing Ca influx) will therefore increase diastolic [Ca ] . This identifies a novel mechanism by which changes of the amplitude of the systolic Ca transient control diastolic [Ca ] .
为了使心脏能够作为一个泵发挥功能，细胞内钙离子浓度([Ca²⁺])必须在收缩期增加以激活收缩，然后在舒张期下降，以使肌丝松弛，心脏充满血液。本研究调查了大鼠心室肌细胞舒张期[Ca²⁺]的控制。我们表明，通过降低肌浆网功能的操作可以增加舒张期[Ca²⁺]。这伴随着收缩期[Ca²⁺]的减少，使得平均[Ca²⁺]保持不变。我们报告说，舒张期[Ca²⁺]是由收缩期 Ca 内流和 Ca 外流之间的平衡控制的。本研究的结果确定了一种新的机制，通过这种机制，收缩期 Ca 瞬变幅度的变化控制舒张期[Ca²⁺]。
细胞内钙离子浓度([Ca²⁺])在舒张期必须足够低，以使心室松弛并充满血液。干扰这一点会损害松弛。负责调节舒张期[Ca²⁺]的因素，特别是肌浆网（SR）和表面膜的相对作用，尚不清楚。我们研究了已知在心力衰竭中发生的 Ca 循环变化对舒张期[Ca²⁺]的影响。使用 Fluo-3 在电压钳制的大鼠心室肌细胞中进行实验。增加刺激频率会增加舒张期[Ca²⁺]。当 SR 功能受到干扰时，这种[Ca²⁺]的增加更大，无论是通过使 Ryanodine 受体渗漏（用咖啡因或 Ryanodine）还是通过用 Thapsigargin 降低肌浆/内质网 Ca-ATP 酶活性。与收缩期 Ca 瞬变幅度降低相关的舒张期[Ca²⁺]的增加使得平均[Ca²⁺]没有变化。时间平均[Ca²⁺]通过异丙肾上腺素的β-肾上腺素能刺激而增加，并随着刺激频率的增加呈饱和方式增加；平均[Ca²⁺]是单位时间内 Ca 内流的线性函数。通过用 50μm 氯化镉减少 L 型 Ca 电流，舒张期和时间平均[Ca²⁺]减少。我们得出结论，舒张期[Ca²⁺]是由收缩期 Ca 内流和外流之间的平衡控制的。此外，降低 Ca 瞬变幅度（不减少 Ca 内流）的操作因此会增加舒张期[Ca²⁺]。这确定了一种新的机制，通过这种机制，收缩期 Ca 瞬变幅度的变化控制舒张期[Ca²⁺]。
