FIBER TYPE-SPECIFIC GENE-EXPRESSION ACTIVATED BY CHRONIC ELECTRICAL-STIMULATION OF ADULT-MOUSE SKELETAL-MUSCLE FIBERS IN CULTURE

1. Fast-twitch skeletal muscle fibres were enzymatically dissociated f rom adult mouse flexor digitorum brevis (FDB) muscles and maintained i n culture without or with chronic low frequency stimulation (one 5 s t rain of 5 Hz pulses per minute) for up to 6 days. Single fibre reverse transcriptase-polymerase chain reaction was conducted to coamplify be ta-myosin heavy chain (beta-MHC) and alpha-skeletal actin mRNA from th e same fibre. 2. Chronic low frequency electrical stimulation of FDB f ibres in culture increased the level of mRNA for beta-MHC. In unstimul ated fibres there was a slight decline in the beta-MHC mRNA level. As an internal control there was no increase in the level of mRNA for alp ha-actin in the identical individual stimulated or unstimulated fibres . 3. Neither the percentage of fibres exhibiting beta-MHC protein nor the Ca2+ transients recorded from individual fibres subjected to the s ame pattern of stimulation showed any difference between stimulated an d unstimulated fibres over the period in culture. 4. This system provi des a convenient in vitro model system for studying activity-dependent control of fibre type-specific gene expression in adult skeletal musc le fibres in culture.