IN-VITRO STUDIES OF THE ULTRASTRUCTURAL-CHANGES INDUCED BY GUANIDINE IN THE NERVES, MUSCLE-FIBERS AND NEUROMUSCULAR-JUNCTION OF THE MOUSE DIAPHRAGM

1. The incubation of mouse isolated diaphragm with guanidine for 60 mi n produced ultrastructural changes in the neuromuscular junction, the intramuscular fascicles of the phrenic nerve and the skeletal muscle f ibers. 2. The main morphological characteristics of both the end termi nals and the nerve fibers were a swollen appearance and an electron-lu cent axoplasm. In addition, the mitochondria in these regions were mar kedly swollen and showed a rarefaction of their cristae as well as a ' 'washed aspect'' of their matrix. Occasional periaxonal vacuoles were present in the myelinated axons. There was a reduction in the number o f synaptic vesicles, which was accentuated by the enlarged areas of th e majority of the terminals. 3. Muscle cells underwent a range of morp hological alterations in the myofibrils and mitochondria. The most dra stic type of necrosis affecting these cells was complete dissolution o f the myofibrils, which resulted in an apparently ''empty'' cell with only the sarcolemma and a few mitochondria remaining intact. 4. Tetrod otoxin was unable to provide total protection against these guanidine- induced changes. 5. We conclude that the ultrastructural effects evoke d by guanidine may be associated with modifications in the permeabilit y of the axolemmal and sarcolemmal membranes as a result of changes in ionic conductance. Such ionic disturbances also interfere with the me tabolism of mitochondria and the sarcoplasmic reticulum and may accoun t for the well known inhibitory effect of guanidine on K+ channels and consequently on Ca2+ and Na+ conductances. 6. It is also suggested th at the guanidine-induced alterations in the presynaptic and postsynapt ic sites could have independent mechanisms of action. (C) 1998 Elsevie r Science Inc.