Fitzgerald R S, Howell S, Jacobus W E
Department of Environmental Health Sciences, Johns Hopkins Medical Institutions, Baltimore, Maryland 21205.
J Appl Physiol (1985). 1988 Nov;65(5):2270-7. doi: 10.1152/jappl.1988.65.5.2270.
We have reported previously that, when exposed to hypercapnia of various intensities, the diaphragm reduces its force of twitch and tetanic contractions in the in vitro rat preparation as well as in the in vivo dog preparation. The experiments reported here with 31P nuclear magnetic resonance (31P-NMR) spectroscopy attempt to examine cellular mechanisms that might be responsible for this deterioration in mechanical performance. Specifically they describe certain characteristics of this preparation and cautions needed to study the resting in vitro rat diaphragm with such techniques. Second, they report the response of intracellular pH (pHi), phosphocreatine (PCr), ATP, and inorganic phosphate (Pi) in the resting in vitro rat diaphragm exposed to long-term normocapnia or to long-term hypercapnia. The results show that 1) to maintain a viable preparation, it was necessary to keep the diaphragm extended to an area approximating that at functional residual capacity, 2) the diaphragm seemed quite capable of maintaining a constant pHi and constant contents of ATP and Pi during normocapnia, but there was a gradual decline in PCr, and 3) during hypercapnia there was a significant decrease in pHi, but the behavior of the phosphate metabolites was exactly as during normocapnia. The results suggest that the decrease in mechanical performance of the diaphragm is probably not due to a decrease in the availability of the high-energy phosphates, although they do not completely exclude this possibility or possibilities related to regional compartmentation.
我们之前曾报道过，当暴露于不同强度的高碳酸血症时，在体外大鼠制备物以及体内犬制备物中，膈肌会降低其单收缩和强直收缩的力量。此处报道的用磷-31核磁共振（31P-NMR）光谱法进行的实验试图探究可能导致这种机械性能下降的细胞机制。具体而言，它们描述了该制备物的某些特征以及用此类技术研究体外静息大鼠膈肌时所需的注意事项。其次，它们报告了体外静息大鼠膈肌在长期正常碳酸血症或长期高碳酸血症下细胞内pH（pHi）、磷酸肌酸（PCr）、三磷酸腺苷（ATP）和无机磷酸盐（Pi）的反应。结果表明：1）为维持一个有活力的制备物，有必要将膈肌伸展至接近功能残气量时的面积；2）在正常碳酸血症期间，膈肌似乎完全有能力维持恒定的pHi以及ATP和Pi的恒定含量，但PCr会逐渐下降；3）在高碳酸血症期间，pHi会显著降低，但磷酸盐代谢物的变化情况与正常碳酸血症期间完全相同。结果表明，膈肌机械性能的下降可能并非由于高能磷酸盐可用性的降低，尽管它们并未完全排除这种可能性或与区域分隔相关的可能性。
