Enzymatic activity and morphological differentiation in de novo innervated human muscle cultures

In the present series of experiments, we studied the effects of developmental neural control on morphological differentiation and on the activity of muscle-specific (creatine kinase, CK; phosphoglycerate mutase, PGAM; phosphorylase, PPL; and phosphofructokinase, PFK) and non-specific (acid maltase, AM; glucose-6-phosphate dehydrogenase, G6PD), human muscle enzymes in de novo innervated muscle cultures. Following innervation of muscle cultures, we noted an increase in the activity of CK, PPL, PFK and AM along with a reduction in G6PD activity. There was also a change of the CK isoenzymes present in the myotubes, i.e. BB and MB are the major isoenzymes in non innervated cultures, but MM becomes predominant following innervation. In the case of PGAM, the only isoenzyme present in the non innervated cultures was BB while the MM isoform appeared only after a prolonged innervation period in most cases--with the exception of AM--these changes in enzyme activity and in the type of isoenzymes present, demonstrate that innervated cultures are more similar to mature muscle. This maturation of enzymatic activity correlates well with the morphological maturation of the myotubes observed following innervation. Such innervated cultures therefore represent a better model with which to study the morphological and biochemical abnormalities associated with neuromuscular diseases.