Journal of Neuroscience, Vol 9, 3709-3719, Copyright © 1989 by Society for Neuroscience
Neuromuscular transmission in diabetes: response to high-frequency activation
Y Schiller and R Rahamimoff
Department of Physiology, Hebrew University Hadassah Medical School, Jerusalem, Israel.
In searching for the cellular correlates of diabetic neuropathy, we
examined the response to tetanic stimulation of diabetic neuromuscular
junctions and of age-matched controls. The experiments were performed on
the soleus nerve muscle preparation of the rat in which diabetes was
induced by streptozotocin. Tetanic potentiation was substantially lower in
diabetic rats. In addition, it was found that the diabetic neuromuscular
junction is more resistant to high-frequency stimulation than normal
age-matched controls, in which such stimulation causes a progressively
increasing number of failures in synaptic transmission. Tetanic failures
cannot be predicted from the stochastic properties of transmitter release
and are due to propagation block of action potentials into the nerve
terminals. The resistance of diabetic nerves to tetanic stimulation is a
function of the duration of diabetes; the earliest significant difference
between the number of tetanic failures in diabetic and normal age-matched
controls was observed after 19 d of diabetes, and this difference grew with
increased duration of diabetes. The resistance to tetanic stimulation in
diabetic rats is reversed by insulin in vivo but not in vitro. Elevation in
extracellular [K+] increases the number of tetanic failures in both
diabetic and normal preparations. Furthermore, elevating extracellular [K+]
to 8.5 mM brings the number of tetanic failures into the range of tetanic
failures in normal nerves. This finding is consistent with the hypothesis
that differences in extracellular [K+] accumulation during high-frequency
stimulation are responsible for the diabetic nerve's relative resistance to
high-frequency stimulation. The lower number of failures corrects only
partially the impaired neuromuscular transmission in the diabetic state,
and there is an overall reduction in tetanic potentiation in diabetes.