PARTIAL TRANSFORMATION FROM FAST TO SLOW MUSCLE-FIBERS INDUCED BY DEAFFERENTATION OF CAPSAICIN-SENSITIVE MUSCLE AFFERENTS

Mechanical and histochemical characteristics of the lateral gastrocnem ius (LG) muscle of the rat were examined 21 days after capsaicin injec tion into the LG muscle. The capsaicin caused a decrease in generation rate of twitch and tetanic tension and an increase in fatigue resista nce of LG muscle. The histochemical muscle fiber profile evaluated by myosin adenosine triphosphatase and reduced nicotinamide adenine dinuc leotide tetrazolium reductase methods showed an increase of type I and IIC fibers and a decrease of the type IIB in whole muscle, and a decr ease of the IIA, IIX fibers in the red part accompanied by their incre ase in the white part. Therefore the capsaicin treatment, which select ively eliminated fibers belonging to the III and IV groups of muscle a fferents, induced muscle fiber transformation from fast contracting fa tiguing fibers to slowly contracting nonfatiguing ones. (C) 1997 John Wiley & Sons, Inc.