Differences in responses of cutaneous afferents in the human median and sural nerves to ischemia

Recent evidence suggests that two conductances responsible for accommodatio n to changes in membrane potential (a slow K+ conductance and inward rectif ication [I-H]) are less active on cutaneous afferents in the sural nerve th an on those in the median nerve, and it has been suggested that these axons would therefore respond differently to stress, whether natural or due to d isease. The present study was undertaken in eight healthy volunteers to det ermine whether these afferents respond differently to the depolarizing and hyperpolarizing stresses that accompany ischemia for 13 min and subsequent recovery. During ischemia, the decrease in threshold was quantitatively les s for the sural afferents, as were the changes in the other indices of axon al excitability, presumably because the ischemic depolarization was less fo r sural afferents. Following release of ischemia, there was, as predicted, a divergence in the pattern of threshold change. With median afferents ther e was evidence of a transient depolarization, believed to be due to inward rectification, superimposed on a longlasting hype rpolarization. The respon se of sural afferents lacked this transient depolarizing threshold change. Cutaneous afferents in the median and sural nerves behave differently in re sponse to ischemic and postischemic stresses, and it is likely that they wi ll also respond differently to disease processes. in a number of respects t he differences between sural and median afferents are analogous to differen ces between diabetic and normal nerves. (C) 2001 John Wiley & Sons, Inc.