Christ Torsten, Schindelhauer Stefan, Wettwer Erich, Wallukat Gerd, Ravens Ursula
Department of Pharmacology and Toxicology, Medical Faculty Carl Gustav Carus, Dresden University of Technology, Dresden, Germany.
J Mol Cell Cardiol. 2006 Oct;41(4):716-23. doi: 10.1016/j.yjmcc.2006.06.011. Epub 2006 Aug 4.
Autoantibodies against the beta1-adrenoceptor (beta1-AAB) in the serum of patients with dilated cardiomyopathy (DCM) are associated with stimulatory effects at cardiac beta1-adrenoceptors. They enhance cardiomyocyte shortening and increase the amplitude of L-type Ca2+ current, ICa. However, in contrast to the unselective beta-adrenoceptor agonist (-)-isoprenaline, beta1-AAB produce positive responses in a fraction of myocytes (responder cells) only and fail to do so in the remaining ones (non-responder cells). To understand this peculiar behaviour, the electrophysiological characteristics of ICa in response to beta1-AAB and (-)-isoprenaline were investigated in responder and non-responder cells. The immunoglobulin G (IgG) fractions containing beta1-AAB (beta1-IgG) were obtained from patients with DCM undergoing immunoabsorption therapy. Only antibody preparations that tested positive in the neonatal rat cardiomyocyte bio-assay by enhancing beating rate were used for further experimentation. Calcium currents were measured with the standard patch clamp technique in adult rat ventricular myocytes. Less than half of all cells exposed to beta1-IgG or purified beta1-AAB were responder cells in which ICa amplitude increased. ICa increase by beta1-IgG or (-)-isoprenaline was reversed by addition of carbachol. Exposure to subtype-selective beta-adrenoceptor blockers indicated that the effects of IgG were mediated via beta1-adrenoceptors. In responder cells, there were no differences between beta1-IgG- and (-)-isoprenaline-induced changes in current-voltage relationship of ICa, in the time constants of fast inactivation, and in steady-state activation and steady-state inactivation curves. (-)-Isoprenaline (1 microM) effectively increased ICa after wash-out of antibody in all cells including non-responder cells. However, when non-responder cells were challenged with (-)-isoprenaline in the presence of beta1-IgG, any further increase in ICa was completely suppressed. Conversely, in responder cells, the cumulative concentration-response curves for (-)-isoprenaline on top of the autoantibodies reached the same maximum ICa amplitude as in control cells. From these interactions we conclude that beta1-AAB not only may enhance ICa via stimulation of beta1-adrenoceptors but also may inhibit beta1-adrenoceptor-mediated increase upon stimulation with catecholamines suggesting a receptor interaction distinct from that with (-)-isoprenaline.
扩张型心肌病（DCM）患者血清中抗β1 - 肾上腺素能受体自身抗体（β1 - AAB）与心脏β1 - 肾上腺素能受体的刺激作用相关。它们增强心肌细胞缩短并增加L型钙电流（ICa）的幅度。然而，与非选择性β - 肾上腺素能受体激动剂（ - ） - 异丙肾上腺素不同，β1 - AAB仅在一部分心肌细胞（反应细胞）中产生阳性反应，而在其余细胞（无反应细胞）中则不然。为了解这种特殊行为，研究了反应细胞和无反应细胞中ICa对β1 - AAB和（ - ） - 异丙肾上腺素反应的电生理特性。含有β1 - AAB的免疫球蛋白G（IgG）组分（β1 - IgG）取自接受免疫吸附治疗的DCM患者。仅使用通过提高搏动率在新生大鼠心肌细胞生物测定中测试呈阳性的抗体制剂进行进一步实验。在成年大鼠心室肌细胞中用标准膜片钳技术测量钙电流。暴露于β1 - IgG或纯化的β1 - AAB的所有细胞中，不到一半是反应细胞，其中ICa幅度增加。添加卡巴胆碱可逆转β1 - IgG或（ - ） - 异丙肾上腺素引起的ICa增加。暴露于亚型选择性β - 肾上腺素能受体阻滞剂表明IgG的作用是通过β1 - 肾上腺素能受体介导的。在反应细胞中，β1 - IgG和（ - ） - 异丙肾上腺素引起的ICa电流 - 电压关系变化、快速失活时间常数以及稳态激活和稳态失活曲线之间没有差异。在包括无反应细胞在内的所有细胞中，冲洗抗体后（ - ） - 异丙肾上腺素（1μM）有效地增加了ICa。然而，当在β1 - IgG存在下用（ - ） - 异丙肾上腺素刺激无反应细胞时，ICa的任何进一步增加都被完全抑制。相反，在反应细胞中，在自身抗体之上（ - ） - 异丙肾上腺素的累积浓度 - 反应曲线达到与对照细胞相同的最大ICa幅度。从这些相互作用中我们得出结论，β1 - AAB不仅可以通过刺激β1 - 肾上腺素能受体增强ICa，而且还可以抑制儿茶酚胺刺激时β1 - 肾上腺素能受体介导的增加，这表明其与（ - ） - 异丙肾上腺素的受体相互作用不同。
