Tang C, Yang J, Wu L L, Dong L W, Liu M S
Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, Missouri 63104, USA.
Am J Physiol. 1998 Apr;274(4):R1078-86. doi: 10.1152/ajpregu.1998.274.4.R1078.
The role of receptor phosphorylation on the redistribution of beta-adrenergic receptors (beta-ARs) in rat hearts during different phases of sepsis was investigated. Sepsis was induced by cecal ligation and puncture (CLP). Changes in the distribution of beta-ARs in the sarcolemmal and light vesicle fractions were studied using (-)-[4,6-propyl-3H]dihydroalprenolol ([3H]DHA). Phosphorylation of beta-ARs was studied by perfusing hearts with [32P]H3PO4 followed by identification of the phosphorylated beta-ARs with immunoprecipitation using anti-beta 1-AR antibody. The results show that septic rat hearts exhibit an initial hypercardiodynamic (9 h after CLP; early sepsis) and a subsequent hypocardiodynamic (18 h after CLP; late sepsis) state. [3H]DHA binding studies show that, during early sepsis, the maximum binding capacity (Bmax) was increased by 26% in sarcolemma but was decreased by 30% in light vesicles, whereas, during late sepsis, the Bmax was decreased by 39% in sarcolemma but increased by 31% in light vesicles. These data indicate that beta-ARs in the rat heart were externalized from light vesicles to sarcolemma during early sepsis but were internalized from surface membranes to intracellular sites during late sepsis. The immunoprecipitation studies reveal that the externalization of beta-ARs during early sepsis was coupled with a concomitant decrease (-28.5 to -30.6%, P < 0.01) in the receptor phosphorylation, whereas the internalization of beta-ARs during late sepsis was accompanied by a simultaneous increase (30.3 to 33.8%, P < 0.01) in the receptor phosphorylation. Because the phosphorylation/dephosphorylation of beta 1-ARs regulate their functional coupling and may reflect their subcellular distribution, it is suggested that the increase in receptor phosphorylation seen in late sepsis leads to the receptor internalization observed in late sepsis; similarly, externalization of (dephosphorylated) receptors in early sepsis may give rise to the apparent decrease in sarcolemmal receptor phosphorylation observed during this interval.
研究了受体磷酸化在脓毒症不同阶段对大鼠心脏中β-肾上腺素能受体（β-ARs）再分布的作用。通过盲肠结扎和穿刺（CLP）诱导脓毒症。使用（-）-[4,6-丙基-3H]二氢阿普洛尔（[3H]DHA）研究肌膜和轻囊泡部分中β-ARs分布的变化。通过用[32P]H3PO4灌注心脏，然后使用抗β1-AR抗体通过免疫沉淀鉴定磷酸化的β-ARs来研究β-ARs的磷酸化。结果表明，脓毒症大鼠心脏表现出初始的高心动力状态（CLP后9小时；早期脓毒症）和随后的低心动力状态（CLP后18小时；晚期脓毒症）。[3H]DHA结合研究表明，在早期脓毒症期间，肌膜中的最大结合容量（Bmax）增加了26%，但轻囊泡中的Bmax降低了30%，而在晚期脓毒症期间，肌膜中的Bmax降低了39%，但轻囊泡中的Bmax增加了31%。这些数据表明，大鼠心脏中的β-ARs在早期脓毒症期间从轻囊泡外化至肌膜，但在晚期脓毒症期间从表面膜内化至细胞内位点。免疫沉淀研究表明，早期脓毒症期间β-ARs的外化与受体磷酸化的同时降低（-28.5%至-30.6%，P<0.01）相关，而晚期脓毒症期间β-ARs的内化伴随着受体磷酸化的同时增加（30.3%至33.8%，P<0.01）。由于β1-ARs的磷酸化/去磷酸化调节其功能偶联并可能反映其亚细胞分布，因此提示晚期脓毒症中观察到的受体磷酸化增加导致了晚期脓毒症中观察到的受体内化；同样，早期脓毒症中（去磷酸化）受体的外化可能导致在此期间观察到的肌膜受体磷酸化明显降低。
