MYONECROSIS INDUCED BY GUANIDINE IN THE MOUSE ISOLATED PHRENIC-NERVE DIAPHRAGM PREPARATION

1. The myonecrosis induced by guanidine in the mouse phrenic nerve dia phragm preparation was investigated using both light microscopy and my ographic recordings. Preparations were incubated with 10 mM guanidine for 60 min in the absence and presence of electrical stimulation. At t he end of this period, the drug was washed out and the nutritive mediu m replaced with fixative solution to prevent morphological artefacts. 2. Guanidine produced a triphasic change in the amplitude of twitch te nsion evoked indirectly through the motor nerve. This response consist ed of an initial facilitation followed by a neuromuscular blockade and a secondary facilitatory effect after removal of the drug. 3. Morphol ogical analysis of the muscle showed various structural alterations of the fibers, including the presence of very dark swollen cells with or without small clear vacuoles, delta lesions with densely or loosely c lumped myofibrils, irregular clear spaces, indistinct masses of degrad ed myofibrils, and, in extreme cases, ''ghost'' cells. All of these ef fects were attributed to the presence of high cytosolic calcium concen trations. 4. Pretreatment with tetrodotoxin (TTX, 3.13 mu M) diminishe d but did not prevent the guanidine-induced morphological abnormalitie s in the muscle cells. This finding suggests that TTX can interfere to a certain extent with the influx of guanidine into muscle fibers thro ugh sodium channels. 5. An attempt was made to correlate the myographi c findings with the muscle morphological alterations seen after guanid ine removal. (C) 1997 Elsevier Science Inc.