Gando S, Hattori Y, Akaishi Y, Nishihira J, Kanno M
Department of Pharmacology, Hokkaido University School of Medicine, Sapporo, Japan.
J Pharmacol Exp Ther. 1997 Jul;282(1):475-84.
The aim of this study was to explore the cellular mechanisms underlying the impaired contractile response to beta adrenoceptor stimulation in diabetic hearts. Chronic diabetes was induced in rats by a streptozotocin injection. Four to six weeks later, papillary muscles isolated from diabetic hearts exhibited marked reductions in the positive inotropic responses to isoproterenol, norepinephrine and epinephrine. The contractile responses to forskolin, 3-isobutyl-1-methylxanthine and dibutylic cyclic AMP were also prominently depressed. The density of beta adrenoceptors was decreased by 50%. However, competitive binding studies with isoproterenol showed no difference in the proportion of beta adrenoceptors with high-affinity binding between control and diabetic myocardial membranes. Determination of the levels of the alpha subunits of Gs and Gi by immunoblotting revealed markedly less expression of Gi in diabetic myocardium. The abilities of isoproterenol, sodium fluoride, 5'-guanylyl imidodiphosphate and forskolin to stimulate adenylate cyclase were preserved well in membranes prepared from diabetic hearts. Nevertheless, neither stimulation of beta adrenoceptors with isoproterenol nor direct activation of adenylate cyclase with forskolin evoked any significant increase in the degree of phosphorylation of phospholamban in diabetic hearts. These results suggest that impaired contractile response to beta adrenoceptor stimulation is not caused by an alteration in the beta adrenoceptors-Gs-adenylate cyclase system, but is possibly caused by an alteration in cellular function beyond the step of adenylate cyclase activation.
本研究的目的是探讨糖尿病心脏中对β肾上腺素能受体刺激的收缩反应受损的细胞机制。通过注射链脲佐菌素诱导大鼠患慢性糖尿病。4至6周后，从糖尿病心脏分离出的乳头肌对异丙肾上腺素、去甲肾上腺素和肾上腺素的正性肌力反应显著降低。对福斯高林、3-异丁基-1-甲基黄嘌呤和二丁酰环磷酸腺苷的收缩反应也明显受到抑制。β肾上腺素能受体的密度降低了50%。然而，用异丙肾上腺素进行的竞争性结合研究表明，对照和糖尿病心肌膜之间具有高亲和力结合的β肾上腺素能受体比例没有差异。通过免疫印迹法测定Gs和Gi的α亚基水平，发现糖尿病心肌中Gi的表达明显减少。在从糖尿病心脏制备的膜中，异丙肾上腺素、氟化钠、5'-鸟苷酰亚胺二磷酸和福斯高林刺激腺苷酸环化酶的能力保存良好。然而，无论是用异丙肾上腺素刺激β肾上腺素能受体，还是用福斯高林直接激活腺苷酸环化酶，都不会引起糖尿病心脏中受磷蛋白磷酸化程度的任何显著增加。这些结果表明，对β肾上腺素能受体刺激的收缩反应受损不是由β肾上腺素能受体-Gs-腺苷酸环化酶系统的改变引起的，而是可能由腺苷酸环化酶激活步骤之后的细胞功能改变引起的。
