Ferrara N, Böhm M, Zolk O, O'Gara P, Harding S E
National Heart and Lung Institute, Imperial College, London, UK.
J Mol Cell Cardiol. 1997 Feb;29(2):439-48. doi: 10.1006/jmcc.1996.0397.
A decline in contractility in myocytes from ageing guinea-pig hearts was demonstrated, which is more pronounced for maximum beta-adrenoceptor-stimulated activity than contraction in high Ca2+. In this study the role of the inhibitory G-proteins (Gi) in this process was investigated. Comparisons were made between young (Y, < 400 g, < 4 weeks), adult (A. > 600 g, > 8 weeks) and senescent guinea pigs (S, 58-65 weeks, 1136 +/- 30 g). Gi alpha activity, detected by pertussis toxin-catalysed ADP ribosylation, was significantly increased in senescent compared to young animals, but immunodetectable levels of Gi alpha were unchanged, beta-adrenoceptor number was decreased by 27% in senescent compared with young animals (P < 0.002). Pertussis toxin treatment increased the maximum response to isoproterenol in contacting myocytes so that there was no longer any significant decline with age. Maximum contraction amplitudes (sarcomere length change, micron) with isoproterenol before pertussis toxin were 0.144 +/- 0.011 (Y, n = 22 animals), 0.104 +/- 0.009 (A. 18) and 0.098 +/- 0.009 (S. 14), P < 0.01 by analysis of variance (ANOVA). Following toxin treatment amplitudes were 0.140 +/- 0.012 (Y. 12), 0.117 +/- 0.010 (A. 10) and 0.117 +/- 0.018 (S. 8), P = N.S. Pertussis toxin treatment also reversed the effects of ageing on contraction and relaxation velocity in isoproterenol. In contrast, the effect of age on contraction amplitude or velocity in maximum Ca2+ was more pronounced after toxin treatment. The EC50 value for isoproterenol increased with age: pertussis treatment decreased the EC50 in each group, but the effect was especially pronounced for senescent animals. There was no significant difference in the concentration-response curves for the negative inotropic effect of adenosine (in the presence of isoprotenerol) between the three age groups before toxin treatment. All effects of adenosine were abolished after pertussis exposure. We conclude that increased Gi alpha activity is likely to contribute to the decreased response to isoproterenol, but not to high Ca2+, in myocytes from ageing guinea-pigs.
已证实衰老豚鼠心脏肌细胞的收缩性下降，与高钙状态下的收缩相比，最大β - 肾上腺素能受体刺激活性的下降更为明显。在本研究中，对抑制性G蛋白（Gi）在此过程中的作用进行了研究。对年轻（Y，体重<400 g，年龄<4周）、成年（A，体重>600 g，年龄>8周）和衰老豚鼠（S，年龄58 - 65周，体重1136±30 g）进行了比较。通过百日咳毒素催化的ADP核糖基化检测到的Giα活性，与年轻动物相比，衰老动物显著增加，但Giα的免疫检测水平未变。与年轻动物相比，衰老动物的β - 肾上腺素能受体数量减少了27%（P<0.002）。百日咳毒素处理增加了收缩期肌细胞对异丙肾上腺素（isoproterenol）的最大反应，因此不再有随年龄增长的显著下降。在百日咳毒素处理前，异丙肾上腺素作用下的最大收缩幅度（肌节长度变化，微米）分别为0.144±0.011（Y组，n = 22只动物）、0.104±0.009（A组，18只）和0.098±0.009（S组，14只），经方差分析（ANOVA）P<0.01。毒素处理后，幅度分别为0.140±0.012（Y组，12只）、0.117±0.010（A组，10只）和0.117±0.018（S组，8只），P值无统计学意义。百日咳毒素处理还逆转了衰老对异丙肾上腺素作用下收缩和舒张速度的影响。相比之下，毒素处理后，年龄对最大钙状态下收缩幅度或速度的影响更为明显。异丙肾上腺素的EC50值随年龄增加：百日咳毒素处理降低了每组的EC50，但对衰老动物的影响尤为明显。在毒素处理前，三个年龄组之间腺苷（在异丙肾上腺素存在下）负性肌力作用的浓度 - 反应曲线无显著差异。百日咳毒素处理后，腺苷的所有作用均被消除。我们得出结论，Giα活性增加可能导致衰老豚鼠肌细胞对异丙肾上腺素反应降低，但对高钙状态下的反应无影响。
