Modulation of gene expression and function of Na+/Ca2+ exchanger

(1)本研究采用新生大鼠心肌细胞培养的H9 c2细胞，观察氟伐他汀（Fly）对心肌型Na^+/Ca^2+交换蛋白（NCX 1）表达水平的影响。氟伐他汀降低了NCX 1 mRNA的表达。这种作用是通过氟伐他汀抑制HMG-CoA还原酶介导的，导致香叶基香叶基吡磷酸耗尽，从而抑制小GTP酶，特别是RhoB。因此，我们得出结论，RhoB参与NCX mRNA的表达。(2)结果发现，溶血磷脂酰胆碱（LPC）可增加NCX 1 mRNA和蛋白的表达。因此，我们研究了LPC增加NCX 1表达的机制。香叶基香叶基转移酶抑制剂抑制LPC对NCX 1表达的影响。我们认为LPC可能通过加速香叶基香叶基转移酶对RhoB进行异戊烯化而激活RhoB，从而增加NCX 1的表达。(3)已知活性氧能增加心肌NCX电流，但其机制尚不清楚。我们发现H_2O_2可增加豚鼠心室肌细胞的NCX 1电流。本研究探讨了H_2O_2增加豚鼠心室肌细胞NCX 1电流的机制。OH清除剂依达拉奉、Gi/o抑制剂百日咳毒素和MEK抑制剂U 0126可抑制H_2O_2的作用。低浓度H_2O_2对NCX 1电流的影响可被PI 3激酶抑制剂vormannin和Na^+/H^+交换抑制剂cariporide所抑制。Src激酶抑制剂PP 2可抑制高浓度H_2O_2的作用。然而，我们不能检测酪氨酸磷酸化的NCX 1的H_2O_2。这些结果表明H_2O_2转化为OH、激活Gi/o和MAP激酶可增强NCX 1的功能。然后，低浓度的OH激活PI 3激酶和Na^+/H^+交换器并激活NCX 1。高浓度的OH激活Src激酶并间接激活NCX 1。

(1) Using H9c2 cells derived from rat neonatal cardiac myocytes, we investigated the effect of fluvastatin (Fly) on the expression levels of cardiac type of Na^+/Ca^<2+> exchanger (NCX1). Fluvastatin decreased NCX1 mRNA. This effect was mediated by inhibition of HMG-CoA reductase by fluvastatin, leading to depletion of geranylgeranyl pirophosphate, which inhibited small GTP ases, especially RhoB. Therefore we concluded that RhoB was involved in NCX mRNA expression.(2) We fond that lisophosphatidylcholine (LPC) increased NCX1 mRNA and protein expression. Therefore we investigated the mechanism of LPC increasing NCX1 expression. An inhibitor of geranylgeranyltransferase inhibited the effect of LPC on NCX1 expression. We propose that LPC may increase NCX1 expression by activating RhoB by accelerating the activity of geranylgeranyltransferase to prenylate RhoB.(3) It had been known that reactive oxygen species increase cardiac NCX current, but its mechanism was unknown. We found that H_2O_2 increased NCX1 current in guinea pig cardiac ventricular cells. We investigated the mechanism of H_20_2 increasing NCX1 current in the ventricular cells of the guinea pig. The effect of H_20_2 was inhibited by a OH scavenger, edaravone; a Gi/o inhibitor, pertussion toxin; and MEK inhibitor U0126. The effect of a low concentration of H_2O_2 on NCX1 current was inhibited by PI3 kinase inhibitor, vormannin; and Na^+/H^+ exchanger inhibitor, cariporide. The effect of a high concentration of H_2O_2 was inhibited by Src kinase inhibitor, PP2. However, we could not detect tyrosin phosphorylation of NCX1 by H_2O_2. These result indicated that NCX1 function was enhanced by H_2O_2 converting to OH, activating Gi/o, and MAP kinase. Then a low concentration of OH activate PI3 kinase and Na^+/H^+ exchanger and activate NCX1. A high concentration of OH activated Src kinase and activate NCX1 indirectly.