EFFECTS OF PROTAMINE ON MYOCARDIAL FUNCTION AND INIRACELLULAR Ca2+ DYNAMICS IN THE ISOLATED RAT HEARTS

我们以前报道过鱼精蛋白本身引起选择性局部血管扩张，肝素通过一氧化氮依赖机制增强鱼精蛋白诱导的血管变化。但一氧化氮系统不参与鱼精蛋白引起的心肌功能障碍。本研究旨在探讨细胞内钙动态变化与鱼精蛋白诱导的大鼠心脏功能障碍的关系。我们还研究了带负电荷的肝素是否会改变鱼精蛋白的毒性心肌效应。在大鼠心脏灌流系统中加入Fura-2/AM作为[Ca~(2+)]i标记物，在鱼精蛋白(20 mg/L)染毒5min后，心肌耗氧量开始和一过性增加，而LV-dp/dt max、收缩[Ca~(2+)]_i和舒张期[Ca~(2+)]_i无明显变化。在鱼精蛋白作用10min时，LV dp/dt max降低，收缩压[Ca~(2+)]i降低。用缓冲液冲洗后，收缩压[钙]i…更多患者在2分钟内恢复到基线水平。而LV-dp/dt-max下降持续10min。鱼精蛋白暴露前给予肝素(2000IU/L)可引起LVdp/dtmax的不良反应。肝素和鱼精蛋白同时给药时，鱼精蛋白本身的负性变力作用减弱。肝素洗涤心脏后，心肌细胞[Ca~(2+)]_i瞬变幅度恢复较快，而LV-dp/dt_(Max)无明显保护作用。提示鱼精蛋白具有直接负性变力作用，其作用机制可能与[Ca~(2+)]_i降低有关。鱼精蛋白还可降低心肌细胞对钙离子的敏感性，从而可能导致再灌流后持续的心肌抑制。鱼精蛋白暴露前肝素的存在可增强鱼精蛋白的负性肌力作用。然而，肝素-鱼精蛋白复合体对心肌功能和[Ca~(2+)]i动力学的影响最小。鱼精蛋白暴露后肝素的存在可促进[Ca~(2+)]_i瞬变幅度的恢复。较少

We have previously reported that protamine itself caused selective regional vasodilation and that heparin potentiated protamine-induced vascular changes via a nitric oxide dependent mechanism. However, nitric oxide system was not involved in protamine induced myocardial dysfunction. This study was designed to assess the relationship between intracellular calcium ([Ca2+]i) dynamics and myocardial dysfunction induced by protamine in the isolated rat hearts. We have also investigated whether negatively charged heparin changes the toxic myocardial effects of protamine. Rat hearts were perfused with a Langendorff system and loaded with Fura-2/AM, as a [Ca2+]i marker.At 5 min after protamine (20 mg/L) exposure, initial and transient increase in myocardial oxygen consumption was observed, whereas LV dP/dt max, systolic [Ca2+]i and diastolic [Ca2+]i did not change yet. At 10 min after protamine, LV dP/dt max decreased and systolic [Ca2+]i decreased. After washout with buffer, systolic [Ca2+]i … More returned to baseline level within 2 min. However, decrease in LV dP/dt max was sustained for 10 min. The presence of heparin (2000 IU/L) prior to protamine exposure resulted in deleterious responses in LV dP/dt max. When heparin and protamine were administered simultaneously, negative inotropic effect of protamine itself was diminished. When the hearts were washed out with heparin, the amplitude of the [Ca2+]i transient recovered more rapidly, whereas no protective response in LV dP/dt max was observed.These results suggested that protamine has a direct negative inotropic effect, which is mediated by a decrease in [Ca2+]i. Protamine also decreases myofilament Ca2+ sensitivity, which may cause sustained myocardial depression after reperfusion. The presence of heparin before protamine exposure enhances negative inotropic effect of protamine. However, heparin-protamine complex has minimum effects on myocardial function and [Ca2+]i dynamics. The presence of heparin after protamine exposure enhances the recovery of the amplitude of the [Ca2+]i transient. Less