Ward C A, Moffat M P
Department of Pharmacology and Toxicology, University of Western Ontario, London, Canada.
Cardiovasc Res. 1995 Feb;29(2):247-53.
The aim was to examine the effects of the Na+/H+ exchange inhibitor methylisobutylamiloride (MIA) as well as protein kinase C, a putative regulator of Na+/H+ exchange, on intracellular calcium, intracellular pH, and unloaded cell shortening in isolated guinea pig cardiac myocytes subjected to lactic acid induced acidosis followed by realkalinisation.
Calcium transient amplitude and cell shortening were measured simultaneously in single isolated myocytes loaded with fura2-AM. Intracellular pH was measured in cells loaded with BCECF-AM.
Exposure of cells to 5 min of lactate (20 mM) acidosis (pH 6.8) caused an increase in calcium transient amplitude and a decrease in cell shortening and intracellular pH. During realkalinisation (pH 7.3), the calcium transient gradually decreased while intracellular pH became more alkaline than pre-acidosis values. The cells underwent transient hypercontractility as evidenced by a marked increase in systolic cell shortening and a decrease in diastolic cell length. Inhibition of sodium/hydrogen exchange with MIA (1 microM) caused a significant attenuation of the increase in calcium transient amplitude during acidosis and further depressed cell shortening as well as intracellular pH. In addition, MIA significantly attenuated hypercontractility and abolished cell contracture upon realkalinisation. In contrast, phorbol 12-myristate 13-acetate (10(-12) M) exerted no effects on the response to acidosis; however, this treatment exacerbated cell hypercontractility and reduced functional recovery upon realkalinisation.
Inhibition of Na+/H+ exchange activity during acidosis/realkalinisation enhances recovery of cell function.
研究钠氢交换抑制剂甲基异丁基阿米洛利（MIA）以及作为钠氢交换假定调节因子的蛋白激酶C对分离的豚鼠心肌细胞内钙、细胞内pH值和无负荷细胞缩短的影响，这些细胞先经历乳酸诱导的酸中毒，随后再进行再碱化。
在加载fura2-AM的单个分离心肌细胞中同时测量钙瞬变幅度和细胞缩短。在加载BCECF-AM的细胞中测量细胞内pH值。
将细胞暴露于5分钟的乳酸（20 mM）酸中毒（pH 6.8）中会导致钙瞬变幅度增加、细胞缩短和细胞内pH值降低。在再碱化过程中（pH 7.3），钙瞬变逐渐降低，而细胞内pH值变得比酸中毒前的值更碱性。细胞经历了短暂的过度收缩，表现为收缩期细胞缩短显著增加和舒张期细胞长度减少。用MIA（1 microM）抑制钠氢交换会导致酸中毒期间钙瞬变幅度增加的显著减弱，并进一步抑制细胞缩短以及细胞内pH值。此外，MIA显著减弱了过度收缩，并消除了再碱化时的细胞挛缩。相比之下，佛波醇12-肉豆蔻酸酯13-乙酸酯（10^(-12) M）对酸中毒反应没有影响；然而，这种处理会加剧细胞过度收缩，并降低再碱化后的功能恢复。
在酸中毒/再碱化期间抑制钠氢交换活性可增强细胞功能的恢复。
