Ch'en Frederick F-T, Dilworth Emma, Swietach Pawel, Goddard Ruth S, Vaughan-Jones Richard D
Burdon Sanderson Cardiac Science Centre, University Laboratory of Physiology, University of Oxford, Parks Road, Oxford OX1 3PT, UK.
J Physiol. 2003 Nov 1;552(Pt 3):715-26. doi: 10.1113/jphysiol.2003.051888. Epub 2003 Aug 15.
Almost all aspects of cardiac function are sensitive to modest changes of temperature. We have examined the thermal sensitivity of intracellular pH regulation in the heart. To do this we determined the temperature sensitivity of pHi, intracellular buffering capacity, and the activity of sarcolemmal acid-extrusion proteins, Na+-H+ exchange (NHE) and Na+-HCO3- co-transport (NBC) in guinea-pig isolated ventricular myocytes. pHi was recorded fluorimetrically with acetoxymethyl (AM)-loaded carboxy-SNARF-1 at either 27 or 37 degrees C. At 27 degrees C, intrinsic (non-CO2-dependent) buffering power (betai) was approximately 60% of that at 37 degrees C. Acid-extrusion (Je) through NHE was approximately 50% slower than at 37 degrees C, consistent with a Q10 of approximately 2. In 5% CO2/HCO3--buffered conditions, in the presence of 30 microM cariporide to inhibit NHE, acid extrusion via NBC was also slowed at 27 degrees C, suggestive of a comparable Q10. Resting pHi at 27 degrees C was similar in Hepes- or 5% CO2/HCO3--buffered superfusates but, in both cases, was approximately 0.1 pH units lower at 37 degrees C. The higher the starting pHi, the larger was the thermally induced fall of pHi, consistent with a mathematical model where intrinsic buffers with a low principal pKa (e.g. close to 6.0) are less temperature-sensitive than those with a higher pKa. The high temperature sensitivity of pHi regulation in mammalian cardiac cells has implications for experimental work conducted at room temperature. It also has implications for the ability of intracellular acidosis to generate intracellular Na+ and Ca2+ overload, cardiac injury and arrhythmia in the heart.
心脏功能的几乎所有方面对适度的温度变化都很敏感。我们研究了心脏中细胞内pH调节的热敏感性。为此，我们测定了豚鼠离体心室肌细胞中细胞内pH（pHi）、细胞内缓冲能力以及肌膜酸排出蛋白、钠氢交换体（NHE）和钠-碳酸氢根共转运体（NBC）活性的温度敏感性。使用乙酰氧基甲基（AM）负载的羧基-磺酸萘酰亚胺荧光染料（carboxy-SNARF-1）在27℃或37℃下通过荧光法记录pHi。在27℃时，固有（非二氧化碳依赖性）缓冲能力（betai）约为37℃时的60%。通过NHE的酸排出（Je）比37℃时慢约50%，这与约为2的Q10值一致。在5%二氧化碳/碳酸氢根缓冲条件下，在存在30μM卡立泊来德抑制NHE的情况下，通过NBC的酸排出在27℃时也减慢，提示有类似的Q10值。在Hepes或5%二氧化碳/碳酸氢根缓冲的灌流液中，27℃时的静息pHi相似，但在两种情况下，37℃时的静息pHi均约低0.1个pH单位。起始pHi越高，热诱导的pHi下降越大，这与一个数学模型一致，即主要pKa较低（例如接近6.0）的固有缓冲剂比pKa较高的缓冲剂对温度更不敏感。哺乳动物心脏细胞中pHi调节的高温敏感性对在室温下进行的实验工作有影响。它还对细胞内酸中毒导致心脏细胞内钠和钙超载、心脏损伤及心律失常的能力有影响。
