CALCIUM AND CYCLIC NUCLEOTIDE DEPENDENT REGULATORY MECHANISMS DURING DEVELOPMENT OF CHICK-EMBRYO SKELETAL-MUSCLE

Late prenatal and early postnatal development of skeletal muscle regulatory systems was studied in chick embryos from 7 days before to 7 days after hatching. The following protein concentrations or enzyme activities were measured daily in pectoralis and in leg muscle extracts: paralbumin, calmodulin (the heat-stable ubiquitous calcium-dependent regulator), calcium-calmodulin-dependent myosin light-chain kinase, cyclic adenosine 3',5'-monophosphate (cAMP) dependent and independent protein kinases, and the heat-stable protein kinase inhibitor. The appearance of adult contractile properties did not correlate with variations in cAMP-dependent protein kinases or the protein kinase inhibitor, which are already present at day -7 and continue to fluctuate around the same level. Muscle development is accompanied by a decrease of cAMP-independent protein kinase activity, which becomes minimal at days +1 to +3, and of the calmodulin content after day +3. These changes may be ascribed to the decrease in the percentage of proliferating cells. By contrast, the synthesis of calcium-modulated myosin light-chain kinase and parvalbumin occurs around the time of hatching, together with that of the sarcoplasmic reticulum Ca2+-Mg2+-ATPase [Martonosi, A., Roufa, D„ Boland, R., Reyes, E„ & Tillack, T. W. (1977) J. Biol. Chem. 252, 318-332], Myosin light-chain kinase activity, initially low, increases rapidly from day -2 to reach a maximum at day +3 to +4. Similarly, parvalbumin, measured by a sensitive radioimmunoassay, is almost absent from all types of muscle until day -2. Active synthesis first begins in leg muscles and then in pectoralis muscle several days later (day +4) and at a much lower rate. cAMP-dependent protein kinase (and its inhibitor) and calmodulin, the ubiquitous regulatory proteins which mediate the effects of cAMP and Ca2+ ions, respectively, are synthesized early in embryonic development. Fast muscle differentiation, which involves the switch off of slow-twitch muscle myosin and the withdrawal of multiple innervation [Gauthier, G. F., Lowey, S., & Hobbs, A. W. (1978) Nature (London) 274, 25-29], is more closely correlated with the late synthesis of the elements of the calcium cycle, namely, the sarcoplasmic reticulum Ca2+ pump, the calcium-dependent myosin light-chain kinase, and the soluble relaxing factor, parvalbumin. © 1979, American Chemical Society. All rights reserved.