Xu Y J, Botsford M W, Panagia V, Dhalla N S
Institute of Cardiovascular Sciences, St Boniface General Hospital Research Centre, Winnipeg, Manitoba.
Can J Cardiol. 1996 Oct;12(10):1092-8.
In view of the crucial role of phosphatidic acid (PA) in signal transduction and Ca(2+)-handling in myocardium, it was the objective of this study to examine the effects of PA on cardiac contractile force and intracellular free Ca2+ in control and chronic diabetic rats.
Diabetes was induced in rats by a single intravenous injection of streptozotocin (65 mg/kg.) and the animals were used for experiments eight weeks after the injection. Heart function was measured by using the isolated perfused heart preparations, and values for systolic pressure, diastolic pressure, rate of contraction (+dP/dt) and rate of relaxation (-dP/dt) were monitored. Intracellular free Ca2+ in cardiomyocytes was estimated by employing Fura-2/AM method.
PA (5 x 10(-8) to 1 x 10(-5) M) produced a concentration-dependent increase in +dP/dt and -dP/dt in the isolated heart; however, these responses were significantly attenuated in diabetic hearts. ATP also caused a positive inotropic effect at concentrations of 1 x 10(-5) to 1 x 10(-4) M but the magnitude of these responses was similar in both control and diabetic groups. Using freshly isolated cardiomyocytes and Fura-2 technique, PA (1 x 10(-6) to 1 x 10(-4) M) was observed to evoke a concentration-dependent increase in [Ca2+]i in both control and diabetic groups. The EC50 and EC95 values for PA were not different but the maximum increase of [Ca2+]i in diabetic hearts was significantly lower in comparison to the control group (152 +/- 41 versus 304 +/- 56 nM). On the other hand, no difference in the increase of [Ca2+]i due to ATP or potassium chloride was seen between control and diabetic cardiomyocytes. Adrenaline pretreatment enhanced [Ca2+]i responses to ATP and PA in both groups; however, the PA-induced increase in [Ca2+]i, unlike the ATP-induced increase, was lower in the diabetic group compared to the control cells with similar pretreatment with adrenaline. The diminished increase in [Ca2+]i due to PA was also observed in cardiomyocytes obtained from rats in which diabetes was induced by intravenous alloxan (65 mg/kg).
PA induced [Ca2+]i mobilization and positive inotropic response were depressed in diabetic heart; this defect in the signal transduction mechanism may contribute to the lower tonic responses of certain inotropic agents in chronic diabetes.
鉴于磷脂酸（PA）在心肌信号转导和钙处理中的关键作用，本研究旨在探讨PA对正常和慢性糖尿病大鼠心脏收缩力及细胞内游离钙的影响。
通过单次静脉注射链脲佐菌素（65mg/kg）诱导大鼠糖尿病模型，注射后8周用于实验。采用离体灌注心脏标本测量心脏功能，监测收缩压、舒张压、收缩速率（+dP/dt）和舒张速率（-dP/dt）。采用Fura-2/AM法估算心肌细胞内游离钙。
PA（5×10⁻⁸至1×10⁻⁵M）使离体心脏的 +dP/dt 和 -dP/dt 呈浓度依赖性增加；然而，糖尿病心脏中的这些反应明显减弱。ATP在浓度为1×10⁻⁵至1×10⁻⁴M时也产生正性肌力作用，但对照组和糖尿病组这些反应的幅度相似。使用新鲜分离的心肌细胞和Fura-2技术，观察到PA（1×10⁻⁶至1×10⁻⁴M）在对照组和糖尿病组中均引起[Ca²⁺]i浓度依赖性增加。PA的EC50和EC95值无差异，但糖尿病心脏中[Ca²⁺]i的最大增加量与对照组相比显著降低（152±41对304±56nM）。另一方面，对照组和糖尿病心肌细胞因ATP或氯化钾引起的[Ca²⁺]i增加无差异。肾上腺素预处理增强了两组对ATP和PA的[Ca²⁺]i反应；然而，与ATP诱导的增加不同，糖尿病组中PA诱导的[Ca²⁺]i增加低于用肾上腺素进行类似预处理的对照组细胞。在静脉注射四氧嘧啶（65mg/kg）诱导糖尿病的大鼠的心肌细胞中也观察到PA引起的[Ca²⁺]i增加减少。
糖尿病心脏中PA诱导的[Ca²⁺]i动员和正性肌力反应减弱；信号转导机制的这种缺陷可能导致慢性糖尿病中某些正性肌力药物的张力反应降低。
