TWO ISOFORMS OF NA,K-ATPASE IN THE HEART

本项目的总体目标是阐明 生理和药理学意义以及生物化学 Na ~+，K ~+ -ATP酶的两种分子形式的调节 雪貂的心 我们已经证明了两种分子形式的 Na ~+，K ~+-ATP酶存在于雪貂心肌细胞中， 高（α（α（+））和低（α） 分子与形式对应的高和低亲和力 哇巴因结合位点。 同工酶抑制 哇巴因引起的双相正性肌力作用表明 这两种α亚单位都是药理学受体 强心苷 Na+，K+-ATP酶同工酶 广泛分布于不同的细胞类型中， 心脏钠泵两种亚型的意义 细胞未知。 雪貂的心脏提供了一个独特的机会， 这些研究。 在拟定研究中，将进行以下实验： 1)可能的生理意义的两个亚型的 将检查钠泵。 假设alpha（+）和alpha 不同形式的钠泵以不同的速率工作， 优先调节Na泵的α（+）形式， 测试. 胰岛素已被证明可以刺激α（+）形式的 脂肪细胞的钠泵对α形式的 泵 2)α（+）形式的相对丰度在 新生儿和出生后早期发育。 的假设 这些变化与药理学变化密切相关， 影响的糖苷和低亲和力的“新生儿”形式 在不同物种的早期发育过程中是常见的， 测试. 3)这一假说认为， 糖苷的α亚基是由于 磷酸酶的周转率和/或稳定性将 考察 4)假设心肌肥大改变了 同工酶谱和因此心脏的糖苷敏感性 会得到考验 5)甲状腺激素调节广泛的 生理功能包括肌球蛋白的表达 同工酶和Na+，K+-ATP酶单位总数。因此，我们认为， 假设甲状腺激素调节 将测试α亚基的两种同种型。 这些研究的结果将表明， Na ~+，K ~+-ATP酶两种亚型的相对丰度低于 激素控制或受心肌肥大影响，以及 这些变化与对药物敏感性的改变有关。 洋地黄苷

The overall objective of this project is to elucidate the physiological, and pharmacological significance and biochemical regulation of the two molecular forms of Na+,K+ -ATPase in the ferret heart. We have demonstrated that two molecular forms of Na+,K+-ATPase exist in ferret myocardial cells in approximately equal abundance; the high (alpha(alpha(+)) and the low (alpha) molecular with forms correspond to the high and low affinity ouabain binding sites, respectively. Inhibition of the isoenzymes by ouabain caused biphasic positive inotropic effects indicating that both of the alpha subunits are the pharmacological receptors for the cardiac glycosides. Although isoenzymes of Na+,K+-ATPase are widely distributed in different cell types, the physiological significance of having two isoforms of the Na pump in the cardiac cells is unknown. Ferret heart offers a unique opportunity for these studies. In the proposed study, the following experiments will be performed: 1) Possible physiological significance of the two isoforms of the Na pump will be examined. The hypothesis that alpha(+) and alpha forms of the Na pump operate at different rates and that insulin preferentially regulates the alpha(+) form of the Na pump will be tested. Insulin has been shown to stimulate the alpha(+) form of the Na pump of fat cells with no effect on the alpha form of the pump. 2) Relative abundance of the alpha(+) form increases during neonatal and early postnatal development. The hypothesis that these changes are closely related to changes in pharmacological effects of the glycoside and that a low affinity "neonatal" form is common among different species during early development will be tested. 3) The hypothesis that differences in affinity of the alpha subunits for the glycoside results from differences in turnover rate and/or stability of the phosphoenzymes will be examined. 4) The hypothesis that myocardial hypertrophy alters isoenzyme profiles and therefore glycoside sensitivity of the heart will be tested. 5) Thyroid hormone regulates a wide range of physiological functions including the expression of myosin isoenzymes and the total number of Na+,K+-ATPase units. Therefore, the hypothesis that thyroid hormone regulates the expression of the two isoforms of alpha subunits will be tested. Results of these studies will indicate if the relative activity or the relative abundance of two isoforms of Na+,K+-ATPase is under hormonal control or is affected by myocardial hypertrophy, and these changes are associated with alterations in sensitivity to the digitalis glycosides.