SKELETAL-MUSCLE OF A GROWING ORGANISM HAS A GREATER TRANSFORMATION AFTER ELECTRICAL-STIMULATION THAN ADULT SKELETAL-MUSCLE

Six adult sheep and four newborn lambs (5 days old) were implanted wit h stimulator leads into the latissimus dorsi muscle and connected to a Myostim 7220 pacing system (Telectronics Pacing Systems, Inc., Englew ood, CO). Electrical stimulation was started immediately after the ope ration. After 8 weeks of electrical stimulation, contractile force (CF ) in adult sheep decreased to 76-81%, and to 78-82% in lambs. After 2 weeks' delay, CF in adults was 96-98%, and only 89-93% in lambs. After a 30 min intensive stress test, unconditioned control muscle lost 39% in lambs and 43% in adults. Muscle conditioned for 8 weeks lost 7-8% CF. However, after 2 weeks' delay, CF in adult muscle lost 33%, but on ly 12% in lambs. After cessation of electrical stimulation, the LDH-5 and LDH-1 + 2 fractions reverted to initial levels in adults, whereas in lambs, these levels continued to follow trends established during e lectrical stimulation. In both adults and lambs, the percent area occu pied by the mitochondria increased during electrical stimulation by 6. 9% in adults and 6.5% in lambs. After electrical stimulation cessation , the percent area in adults returned to baseline levels, whereas it c ontinued to be elevated in lambs (3.3% vs 5.1%, respectively). The tra nsformed muscle of the lamb did not revert to baseline levels after a delay period.