Haimovici J, Beck J S, Molla-Hosseini C, Vallerand D, Haddad P
Department of Pharmacology, Université de Montréal, Québec, Canada.
Am J Physiol. 1994 Sep;267(3 Pt 1):G364-70. doi: 10.1152/ajpgi.1994.267.3.G364.
Indirect evidence suggests that insulin, like epidermal growth factor (EGF), stimulates liver cell Na+/H+ exchange. We directly studied the effect of insulin on intracellular pH (pHi) and the Na+/H+ exchanger in isolated rat hepatocytes with the fluorescent probe, 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). The effects of insulin were compared with those of EGF. Studies were carried out in the absence of HCO3- and in the presence of acetazolamide to isolate the Na+/H+ exchanger from other pH regulatory mechanisms. Insulin (9 nM) caused a reversible acidification of baseline pHi, whereas no significant effect was observed with EGF (30 nM). pHi was acidified by two different methods (NH4Cl pulse and external Na+ removal) to assess liver cell Na+/H+ exchange activity. In the NH4Cl pulse experiments, insulin had no significant effect on the Na+/H+ exchanger compared with the control (0.141 +/- 0.009 pH units/min, n = 14, and 0.122 +/- 0.023 pH units/min, n = 16, respectively). However, in the same conditions, EGF nearly doubled the rate of the Na+/H+ exchange activity (0.193 +/- 0.015 pH units/min, P < 0.05, n = 6). In the Na+ removal experiments, EGF again significantly increased the pHi recovery rate (0.542 +/- 0.032 pH units/min, n = 3) compared with the control (0.227 +/- 0.028 pH units/min, n = 5) and insulin (0.245 +/- 0.053 pH units/min, n = 5). Compared with control conditions, a subchronic administration of insulin (9 nM) in vitro had no significant effect on the Na+/H+ exchanger, nor did it affect baseline pHi.(ABSTRACT TRUNCATED AT 250 WORDS)
间接证据表明，胰岛素与表皮生长因子（EGF）一样，可刺激肝细胞的Na⁺/H⁺交换。我们使用荧光探针2'，7'-双（2-羧乙基）-5（6）-羧基荧光素（BCECF），直接研究了胰岛素对分离的大鼠肝细胞内pH值（pHi）和Na⁺/H⁺交换体的影响。将胰岛素的作用与EGF的作用进行了比较。研究在无HCO₃⁻且存在乙酰唑胺的条件下进行，以将Na⁺/H⁺交换体与其他pH调节机制区分开来。胰岛素（9 nM）导致基线pHi可逆性酸化，而EGF（30 nM）未观察到显著作用。通过两种不同方法（NH₄Cl脉冲和去除细胞外Na⁺）使pHi酸化，以评估肝细胞的Na⁺/H⁺交换活性。在NH₄Cl脉冲实验中，与对照组相比，胰岛素对Na⁺/H⁺交换体无显著影响（分别为0.141±0.009 pH单位/分钟，n = 14，和0.122±0.023 pH单位/分钟，n = 16）。然而，在相同条件下，EGF使Na⁺/H⁺交换活性速率几乎翻倍（0.193±0.015 pH单位/分钟，P < 0.05，n = 6）。在去除Na⁺实验中，与对照组（0.227±0.028 pH单位/分钟，n = 5）和胰岛素组（0.245±0.053 pH单位/分钟，n = 5）相比，EGF再次显著提高了pHi恢复速率（0.542±0.032 pH单位/分钟，n = 3）。与对照条件相比，体外亚慢性给予胰岛素（9 nM）对Na⁺/H⁺交换体无显著影响，也不影响基线pHi。（摘要截短于250字）
