Oron Y, Gillo B, Straub R E, Gershengorn M C
Department of Medicine, Cornell University Medical College, New York, New York 10021.
Mol Endocrinol. 1987 Dec;1(12):918-25. doi: 10.1210/mend-1-12-918.
TRH evoked a complex electrical membrane response in Xenopus laevis oocytes injected with either total cytosolic or poly(A)(+)-enriched RNA from GH3 pituitary cells but not in uninjected oocytes. A typical response consisted of a transient, rapid depolarizing current followed by a prolonged depolarizing current with superimposed current fluctuations. The reversal potentials of the rapid and the slow components of the response were -23.0 and -22.6 mV, respectively, and were markedly affected by CI- concentration indicating that the TRH response was mainly an increase in Cl- conductance. The response to TRH was dose dependent and was inhibited by the TRH antagonist, chlordiazepoxide. TRH caused rapid hydrolysis of labeled phosphatidylinositol 4,5-bisphosphate and a marked, prolonged increase in 45Ca2+ efflux from injected oocytes. The depolarizing response to TRH was not diminished in oocytes incubated in a Ca2(+)-free medium, but was inhibited by microinjection of EGTA. These data suggest that TRH evokes an electrophysiological response in oocytes injected with RNA from GH3 cells via activation of the same biochemical pathway that mediates its actions in GH3 cells. This pathway involves hydrolysis of phosphatidylinositol 4,5-bisphosphate, forming inositol trisphosphate that causes mobilization of cellular Ca2+. We suggest that oocytes injected with GH3 cell RNA, because of their large size and easy access to their intracellular milieu, will be a useful intact cell model in which to define the molecular details of signal transduction by TRH.
促甲状腺激素释放激素（TRH）在注射了来自GH3垂体细胞的总胞质RNA或富含聚腺苷酸（poly(A)）的RNA的非洲爪蟾卵母细胞中诱发了复杂的膜电反应，但在未注射的卵母细胞中未诱发。典型的反应包括一个短暂、快速的去极化电流，随后是一个持续时间较长的去极化电流，并伴有叠加的电流波动。反应的快速和慢速成分的反转电位分别为-23.0和-22.6 mV，且受到氯离子浓度的显著影响，表明TRH反应主要是氯离子电导的增加。对TRH的反应呈剂量依赖性，并受到TRH拮抗剂氯氮卓的抑制。TRH导致标记的磷脂酰肌醇4,5-二磷酸快速水解，并使注射了RNA的卵母细胞中的45Ca2+外流显著且持续增加。在无钙培养基中孵育的卵母细胞对TRH的去极化反应并未减弱，但通过显微注射乙二醇双四乙酸（EGTA）可抑制该反应。这些数据表明，TRH通过激活在GH3细胞中介导其作用的相同生化途径，在注射了来自GH3细胞RNA的卵母细胞中诱发电生理反应。该途径涉及磷脂酰肌醇4,5-二磷酸的水解，形成肌醇三磷酸，进而导致细胞内Ca2+的动员。我们认为，注射了GH3细胞RNA的卵母细胞，因其体积大且易于接触其细胞内环境，将成为一个有用的完整细胞模型，可用于确定TRH信号转导的分子细节。
