Beekman R E, van Hardeveld C, Simonides W S
Laboratory for Physiology, Free University, Amsterdam, The Netherlands.
Biochem J. 1989 Apr 1;259(1):229-36. doi: 10.1042/bj2590229.
The effects of beta-adrenergic stimulation on the relaxation rate and the Ca2+-transport rate in sarcoplasmic reticulum of hypothyroid, euthyroid and hyperthyroid rat hearts were studied. Administration of isoproterenol (0.1 microM) to perfused, electrically stimulated hearts (5 Hz) caused a decrease in the half-time of relaxation (RT 1/2) the extent of which depended on the thyroid status, i.e. hypothyroid (-24%), euthyroid (-19%) or hyperthyroid (-8%). A similar decreasing effect was found for the stimulation of Ca2+ transport in isolated SR by cyclic AMP and protein kinase, i.e. hypothyroid (75%), euthyroid (37%) and hyperthyroid (20%). These alterations were not due to differences in endogenous protein kinase activity or cyclic AMP production. Estimations of Ca2+-ATPase and phospholamban (PL) content of the sarcoplasmic reticulum were obtained by measurement of the phosphorylated forms of Ca2+-ATPase (E-P) and phospholamban (PL-P) followed by electrophoresis and autoradiography. A 3-fold decrease of PL-P, accompanied by a 2-fold increase of E-P per mg of protein was observed in sarcoplasmic reticulum preparations in the direction hypothyroid----hyperthyroid. Consequently the E-P/PL-P ratio increased from 0.32 (hypothyroid), through 0.81 (euthyroid) to 1.69 (hyperthyroid). In spite of certain limitations inherent to quantification of Ca2+-ATPase and phospholamban by their phosphorylated products, these data provide strong evidence that during thyroid-hormone mediated cardiac hypertrophy, with concomitant proliferation of the sarcoplasmic reticulum, the relative amount of phospholamban decreases with respect to Ca2+-ATPase. This could provide an explanation for the observed gradual diminishment of the beta-adrenergic effect on the relaxation rate when cardiac tissue is exposed to increasing amounts of thyroid hormone.
研究了β-肾上腺素能刺激对甲状腺功能减退、甲状腺功能正常和甲状腺功能亢进大鼠心脏肌浆网舒张速率和Ca2+转运速率的影响。对灌注的、电刺激的心脏（5Hz）给予异丙肾上腺素（0.1μM），导致舒张半衰期（RT 1/2）缩短，其缩短程度取决于甲状腺状态，即甲状腺功能减退（-24%）、甲状腺功能正常（-19%）或甲状腺功能亢进（-8%）。环磷酸腺苷（cAMP）和蛋白激酶对分离的肌浆网中Ca2+转运的刺激也有类似的降低作用，即甲状腺功能减退（75%）、甲状腺功能正常（37%）和甲状腺功能亢进（20%）。这些改变并非由于内源性蛋白激酶活性或cAMP产生的差异。通过测量Ca2+ -ATP酶（E-P）和受磷蛋白（PL）的磷酸化形式，然后进行电泳和放射自显影，来估计肌浆网中Ca2+ -ATP酶和受磷蛋白（PL）的含量。在肌浆网制剂中，从甲状腺功能减退到甲状腺功能亢进的方向，观察到每毫克蛋白质的PL-P降低了3倍，同时E-P增加了2倍。因此，E-P/PL-P比值从0.32（甲状腺功能减退）增加到0.81（甲状腺功能正常），再增加到1.69（甲状腺功能亢进）。尽管通过其磷酸化产物对Ca2+ -ATP酶和受磷蛋白进行定量存在一定局限性，但这些数据提供了有力证据，即在甲状腺激素介导的心脏肥大过程中，随着肌浆网的增殖，受磷蛋白相对于Ca2+ -ATP酶的相对量减少。这可以解释当心脏组织暴露于越来越多的甲状腺激素时，β-肾上腺素能对舒张速率的影响逐渐减弱的现象。
