CHANGES IN RESPONSIVENESS TO EXTRACELLULAR ATP IN CHICK SKELETAL-MUSCLE DURING DEVELOPMENT AND UPON DENERVATION

Skeletal muscles in developing chick embryos were tested for responsiv eness to adenosine 5'-triphosphate (ATP), a substance known to depolar ize chick skeletal muscle in culture. The sensitivity to extracellular ATP was tested at various stages of development in five different mus cles; pectoralis superficia, anterior latissimus dorsi, posterior lati ssimus dorsi, sartorious, and gastrocnemius. At the earliest time that muscles were tested (Embryonic Day 6, stage 30 of Hamburger and Hamil ton, 1951) application of ATP (50-100 mu M) elicited vigorous contract ions in all five muscles, but within a few days (Embryonic Day 17, sta ge 43) none of the muscles contracted in response to ATP. Sensitivity declined at approximately the same time in all five of these muscles. Intracellular recordings made from muscle fibers near the time of hatc hing (Embryonic Days 18-21 or Postnatal Days 1-2) indicated that the l oss of the ability to contract in response to ATP was due to the total loss of responsiveness to ATP. Surgical denervation of the anterior l atissimus dorsi and posterior latissimus dorsi was performed in a seri es of chicks 1-2 days after hatching, and the ability of these muscles to contract in response to ATP was tested 3-10 days after the surgery . Contractions in response to ATP were present in many of the muscles. Thus denervation of muscles in newly hatched chicks led to the reappe arance of sensitivity to ATP. The disappearance of ATP responsiveness shortly after muscles become innervated and the reappearance of ATP re sponsiveness following denervation suggest that the expression of ATP responsiveness is regulated by motor neurons. (C) 1995 Academic Press, Inc.