Fukuzawa J, Osaki J, Haneda T
First Department of Internal Medicine, Asahikawa Medical College, Japan.
Clin Exp Hypertens. 1994 Nov;16(6):835-52. doi: 10.3109/10641969409078029.
The purpose of the present study were to determine the contribution of Na+/H+ exchange to pressure overload-induced cardiac hypertrophy and to examine its potential interaction with cAMP-dependent signaling pathway. Isolated rat hearts were perfused as Langendorff preparations with aortic pressure of 60 mmHg. In pressure overload group, aortic pressure was increased to 120 mmHg. cAMP contents in the heart perfused at 2 min were examined by RIA. Rates of protein synthesis were examined by 14C-phenylalanine incorporation into myocardial protein during the second hour of perfusion. Expression of c-fos mRNA in the heart perfused at 1 hour was analyzed by Northern blotting. Elevation of aortic pressure from 60 mmHg to 120 mmHg in perfused rat hearts increased cAMP contents from 4.89 +/- 0.09 to 6.30 +/- 0.28 pmol/mg protein and accelerated rates of protein synthesis from 644 +/- 13 to 860 +/- 49 mmol Phe/g dry heart/hr. Expression of c-fos mRNA was induced by elevated aortic pressure. Amiloride, an inhibitor of Na+/H+ exchange, decreased rates of protein synthesis in a concentration-dependent manner (12.5, 25, 50, 100 microM) but did not change cAMP content (5.25 +/- 0.11 pmol/mg protein) or expression of c-fos mRNA. Furthermore, amiloride did not prevent the increases in cAMP (6.99 +/- 0.34 pmol/mg protein), protein synthesis rates (476 +/- 18 to 689 +/- 31 nmolPhe/g dry heart/hr) and expressions of c-fos mRNA that were induced by elevation of aortic pressure. These results indicate that amiloride, an inhibitor of Na+/H+ exchange system, while influencing rates of protein synthesis, does not play an important role in pressure overload-induced cardiac hypertrophy. The mechanism by which amiloride influences cardiac protein synthesis is independent of the cAMP-dependent mechanism by which pressure overload induces cardiac hypertrophy.
本研究的目的是确定Na+/H+交换对压力超负荷诱导的心肌肥大的作用，并研究其与环磷酸腺苷（cAMP）依赖性信号通路的潜在相互作用。将离体大鼠心脏制备成Langendorff灌流标本，主动脉压力维持在60 mmHg。在压力超负荷组中，将主动脉压力升高至120 mmHg。用放射免疫分析法（RIA）检测灌流2分钟时心脏中的cAMP含量。在灌流的第二个小时期间，通过14C-苯丙氨酸掺入心肌蛋白来检测蛋白质合成速率。用Northern印迹法分析灌流1小时时心脏中c-fos mRNA的表达。在灌流的大鼠心脏中，主动脉压力从60 mmHg升高至120 mmHg，使cAMP含量从4.89±0.09增加至6.30±0.28 pmol/mg蛋白，并使蛋白质合成速率从644±13加快至860±49 mmol苯丙氨酸/g干重心脏/小时。主动脉压力升高诱导了c-fos mRNA的表达。Na+/H+交换抑制剂阿米洛利以浓度依赖性方式（12.5、25、50、100 μM）降低蛋白质合成速率，但不改变cAMP含量（5.25±0.11 pmol/mg蛋白）或c-fos mRNA的表达。此外，阿米洛利不能阻止主动脉压力升高所诱导的cAMP增加（6.99±0.34 pmol/mg蛋白）、蛋白质合成速率加快（476±18至689±31 nmol苯丙氨酸/g干重心脏/小时）以及c-fos mRNA表达增加。这些结果表明，Na+/H+交换系统抑制剂阿米洛利虽然影响蛋白质合成速率，但在压力超负荷诱导的心肌肥大中不起重要作用。阿米洛利影响心脏蛋白质合成的机制独立于压力超负荷诱导心肌肥大的cAMP依赖性机制。
