Martin-Caraballo M, Campagnaro P A, Gao Y, Greer J J
Department of Physiology, University of Alberta, Edmonton, Alberta, Canada T6G 2S2.
J Appl Physiol (1985). 2000 Feb;88(2):573-80. doi: 10.1152/jappl.2000.88.2.573.
The following two hypotheses regarding diaphragm contractile properties in the perinatal rat were tested. First, there is a major transformation of contractile and fatigue properties during the period between the inception of inspiratory drive transmission in utero and birth. Second, the diaphragm muscle properties develop to functionally match changes occurring in phrenic motoneuron electrophysiological properties. Muscle force recordings and intracellular recordings of end-plate potentials were measured by using phrenic nerve-diaphragm muscle in vitro preparations isolated from rats on embryonic day 18 and postnatal days 0-1. The following age-dependent changes occurred: 1) twitch contraction and half relaxation times decreased approximately two- and threefold, respectively; 2) the tetanic force levels increased approximately fivefold; 3) the ratio of peak twitch force to maximum tetanic force decreased 2.3-fold; 4) the range of forces generated by the diaphragm in response to graded nerve stimulation increased approximately twofold; 5) the force-frequency curve was shifted to the right; and 6) the propensity for neuromuscular transmission failure decreased. In conclusion, the diaphragm contractile and phrenic motoneuron repetitive firing properties develop in concert so that the full range of potential diaphragm force recruitment can be utilized and problems associated with diaphragm fatigue are minimized.
对围产期大鼠膈肌收缩特性进行了以下两个假设的测试。第一，在子宫内吸气驱动传导开始到出生这段时间内，收缩和疲劳特性发生了重大转变。第二，膈肌肌肉特性的发展在功能上与膈运动神经元电生理特性的变化相匹配。使用从胚胎第18天和出生后0 - 1天的大鼠分离的膈神经-膈肌体外制备物，测量肌肉力量记录和终板电位的细胞内记录。出现了以下与年龄相关的变化：1）单收缩和半松弛时间分别减少了约两倍和三倍；2）强直力量水平增加了约五倍；3）单收缩峰值力量与最大强直力量的比值下降了2.3倍；4）膈肌对分级神经刺激产生的力量范围增加了约两倍；5）力量-频率曲线向右移动；6）神经肌肉传递失败的倾向降低。总之，膈肌收缩和膈运动神经元重复放电特性协同发展，以便能够利用膈肌潜在力量募集的全部范围，并将与膈肌疲劳相关的问题降至最低。
