G蛋白在大鼠心血管对去甲肾上腺素脱敏反应中的作用

Role of G proteins in the cardiovascular adrenergic desensitization of rats

为了研究鸟嘌呤核苷酸结合蛋白（Ｇ蛋白）在慢性输入去甲肾上腺素（ＮＥ）所致大鼠心脏和主动脉对ＮＥ脱敏反应中的作用，采用大鼠皮下植入微量泵持续输入ＮＥ（０．１ｍｇ·ｋｇ－１·ｈ－１）模型，Ｇ蛋白α亚基及其ｍＲＮＡ水平用相应的抗体和ｃＤＮＡ探针按Ｗｅｓｔｅｒｎｂｌｏｔ和Ｎｏｒｔｈｅｒｎｂｌｏｔ法测定．结果显示：输注６ｄＮＥ的大鼠主动脉中Ｇｓα，Ｇｉα和Ｇｏα均显著下降，但其ｍＲＮＡ无显著改变；心房及心室中Ｇｉα显著升高，Ｇｓα，Ｇｏα维持不变，而Ｇｉ２αｍＲＮＡ升高，心房中ＧｓαｍＲＮＡ下降．输入ＮＥ３ｄ的大鼠心房及心室Ｇｉα，Ｇｏα无改变，Ｇｓα４５和４２ｋＤ带显著下降，但５２ｋＤ带升高；心室中ＧｏαｍＲＮＡ的３．８和３．４ｋｂ带显著升高，而心房中５．４ｋｂ带升高，心室Ｇｉ３αｍＲＮＡ下降．上述结果表明输入ＮＥ可引起Ｇ蛋白的动态变化，提示Ｇ蛋白在ＮＥ慢性刺激引起的心血管反应性降低中可能起一定的作用，其早期以Ｇｓ下降为主。

To determine whether alterations in G protein expression contribute to the adrenergic desensitization in the cardiovascular system. Rats were infused subcutaneously with norepinephrine (NE, 0.1 mg·kg1·h1) for 3 or 6 days using osmotic minipumps. G protein α subunits and their mRNAs were then measured in the aorta and heart by using selective antibodies and cDNA probes with Northern blot, dot blot and Western blot analysis. Infusion of NE for 6 days significantly decreased the levels of Gsα, Giα and Goα in the aorta. The mRNAs for the α subunits were not altered in the aorta. In the atrium and ventricle the level of Gsα (45, 42 kD bands) decreased after NE infusion for 3 days but returned to control levels by day 6, the levels of Giα were unaltered after NE infusion for 3 days but increased significantly by day 6, Goα levels did not change at either days. The level of Gi2α mRNA increased after NE infusion for 6 days and may account for the increase of protein. These results demonstrate that expression of G protein α subunits is altered during cardiovascular desensitization,and suggest that alterations of the α subunits contribute to reduced adrenergic responsiveness, the desensitization is due to the decreased levels of Gsα by 3 days and the increased levels of Giα by 6 days of NE infusion.