促甲状腺激素释放激素诱导垂体GH4C1细胞中Na+/H(+)交换激活的特性研究

Characterization of the TRH-induced activation of Na+/H(+)-exchange in pituitary GH4C1 cells.

作者信息

Törnquist K

机构信息

Endocrine Research Laboratory, University of Helsinki, Minerva Foundation, Institute for Medical Research, Finland.

出版信息

Biochim Biophys Acta. 1992 Oct 5;1110(2):165-70. doi: 10.1016/0005-2736(92)90354-o.

DOI:10.1016/0005-2736(92)90354-o

PMID:1390845

Abstract

In the present study in GH4C1 cells, the dependence of TRH-induced activation of Na+/H(+)-exchange on extracellular Na+ and Ca2+ was examined. Furthermore, the effects of both extracellular and intracellular H+ on Na+/H(+)-exchange were investigated. The buffering capacity was 63 +/- 11.8 mM (pH unit)-1 at basal intracellular pH (pHi) of 7.02 +/- 0.02. The initial rate of alkalinization in cells acidified with nigericin increased with increasing concentrations of extracellular Na+ according to simple Michaelis-Menten kinetics. The apparent Km-value for Na+ was 53 +/- 17.5 mM and the Vmax value was 28 +/- 4.5 mM H+/min. Addition of Na+ together with TRH increased Vmax to 56 +/- 6.4 mM H+/min (P < 0.05), while no difference was observed in Km. Decreasing extracellular pH (pHo) decreased the rate of alkalinization of acid-loaded cells, despite a large inward Na+ gradient. Furthermore, a decrease in pHi was necessary to obtain activation of Na+/H+ exchange. At pHi-values close to basal pHi no activation of Na+/H(+)-exchange was obtained. In addition, the results showed that extracellular Ca2+ was necessary for TRH-induced activation of Na+/H+ exchange. Blocking influx of extracellular Ca2+ with Ni2+ abolished the effect of TRH, suggesting that the TRH-induced activation of Na+/H(+)-exchange in GH4C1 cells is dependent on influx of extracellular Ca2+.

摘要

在目前对GH4C1细胞的研究中，检测了促甲状腺激素释放激素（TRH）诱导的Na⁺/H⁺交换激活对细胞外Na⁺和Ca²⁺的依赖性。此外，还研究了细胞外和细胞内H⁺对Na⁺/H⁺交换的影响。在细胞内基础pH（pHi）为7.02±0.02时，缓冲能力为63±11.8 mM（pH单位）⁻¹。用尼日利亚菌素酸化的细胞中，碱化的初始速率根据简单的米氏动力学随细胞外Na⁺浓度增加而增加。Na⁺的表观Km值为53±17.5 mM，Vmax值为28±4.5 mM H⁺/min。Na⁺与TRH一起添加可将Vmax提高到56±6.4 mM H⁺/min（P<0.05），而Km无差异。降低细胞外pH（pHo）会降低酸负荷细胞的碱化速率，尽管存在较大的内向Na⁺梯度。此外，需要降低pHi才能激活Na⁺/H⁺交换。在接近基础pHi的pHi值时，未获得Na⁺/H⁺交换的激活。此外，结果表明细胞外Ca²⁺是TRH诱导的Na⁺/H⁺交换激活所必需的。用Ni²⁺阻断细胞外Ca²⁺的内流消除了TRH的作用，表明TRH诱导的GH4C1细胞中Na⁺/H⁺交换激活依赖于细胞外Ca²⁺的内流。