ABNORMAL AXONAL INWARD RECTIFICATION IN DIABETIC NEUROPATHY

An abnormal axonal membrane conductance might contribute to human diab etic neuropathy. To test this idea, we have compared the threshold cha nges produced by long-lasting (100-200 ms) de- and hyperpolarizing cur rents applied to median motor and sensory axons at the wrist in 63 dia betic patients with those from 50 normal controls and 27 amyotrophic l ateral sclerosis (ALS) patients. Averages of the threshold electrotonu s plots for motor and sensory axons of diabetic patients showed more s ubexcitability during, and slower recovery following, the application of hyperpolarizing currents. Such alterations have been previously fou nd in isolated rat nerves after inhibition of axonal inward rectificat ion by means of cesium ions. The abnormalities in diabetics were posit ively correlated with the age of patients and the presence of neuropat hy, Threshold electrotonus seen in diabetes differed strongly from the effects of acute ischemia and were unlike changes recorded in ALS, Th e data indicate that an abnormal inward rectification of peripheral ax ons is associated with diabetic neuropathy. A better understanding of the neurobiology of this conductance might provide information about t he pathophysiology of this disease. (C) 1996 John Wiley & Sons, Inc.