Mogyoros I, Lin C S, Kuwabara S, Cappelen-Smith C, Burke D
Department of Neurology, Prince of Wales Hospital and Prince of Wales Medical Research Institute, University of New South Wales, Sydney, Australia.
Muscle Nerve. 2000 Nov;23(11):1719-26. doi: 10.1002/1097-4598(200011)23:11<1719::aid-mus8>3.0.co;2-w.
In a number of clinical studies, measurement of axonal strength-duration properties has been used to provide indirect insight into conductances at the node of Ranvier, particularly persistent Na(+) conductance. However, the specificity of any changes is limited because other factors can affect strength-duration behavior. The present study was undertaken to define the relationship between different strength-duration measures at rest and at different membrane potentials, and also to determine the limits within which strength-duration behavior can be used as a measure of nodal conductances. The strength-duration time constant (tau(SD)) and rheobase of 20 single motor units in the flexor carpi ulnaris were calculated from thresholds defined using threshold tracking. "True" rheobase and rheobasic latencies were measured using test stimuli of 100-ms duration. For ten units, the technique of latent addition was used to measure threshold changes directly attributable to nodal conductances, and for six units these were compared with strength-duration properties at different membrane potentials. The data indicate that measurements of tau(SD) and rheobase can provide sensitive indicators of conductances present at the node of Ranvier when membrane potential changes. There is a reciprocal relationship between tau(SD) and rheobase for single motor units at different membrane potentials, and this relationship may allow changes in tau(SD) due to depolarization and demyelination to be differentiated.
在一些临床研究中，轴突强度 - 时间特性的测量已被用于间接洞察郎飞结处的电导，特别是持续性钠电导。然而，由于其他因素会影响强度 - 时间行为，任何变化的特异性都受到限制。本研究旨在确定静息状态下以及不同膜电位时不同强度 - 时间测量之间的关系，并确定强度 - 时间行为可作为节点电导测量指标的适用范围。通过使用阈值跟踪定义的阈值，计算了尺侧腕屈肌中20个单运动单位的强度 - 时间时间常数（τ(SD)）和基强度。使用持续时间为100毫秒的测试刺激测量“真实”基强度和基强度潜伏期。对于10个单位，采用潜伏相加技术直接测量可直接归因于节点电导的阈值变化，并将其中6个单位的这些变化与不同膜电位下的强度 - 时间特性进行比较。数据表明，当膜电位变化时，τ(SD)和基强度的测量可以提供郎飞结处存在的电导的敏感指标。在不同膜电位下，单运动单位的τ(SD)和基强度之间存在反比关系，这种关系可能有助于区分由于去极化和脱髓鞘导致的τ(SD)变化。
