Effects of electrical stimulation and tetrodotoxin paralysis on expression of muscle-specific isozymes of four enzymes in aneurally cultured embryonic rat muscle

We studied the effect of electrical stimulation and a sodium channel blocker (tetrodotoxin) on the expression of muscle-specific isozymes of creatine kinase, glycogen phosphorylase, phosphoglycerate mutase, and lactate dehydrogenase in aneurally cultured embryonic rat muscle. Muscle contractile activity slightly accelerated the accumulation of muscle-specific isozyme of creatine kinase in early cultures (4 days of experiment), but no increase in the expression of muscle-specific isozymes of any enzyme was present in older cultures (11 days of experiment). We conclude that muscle contractile activity is not a main regulator of isozyme maturation in this system.

Accumulation of CK-MM is impaired in innervated and contracting cultured muscle fibers of Duchenne muscular dystrophy patients

No specific abnormalities have been reproducibly manifested in aneurally cultured muscle of Duchenne muscular dystrophy (DMD) patients. We now report that the accumulation of the muscle-"specific" isozyme of creatine kinase (CK-MM) was significantly and preferentially impaired in long-term innervated contracting muscle fibers cultured from 4 DMD patients (DMD-InnCMFs) compared to: i) their noninnervated sister-cultured muscle fibers, and ii) innervated contracting control cultured human muscle fibers (Control-InnCHMFs). Accumulation of other muscle-"specific" isozymes (MSIs), viz. glycogen phosphorylase, phosphoglycerate mutase, and lactic dehydrogenase, was not significantly impaired. We have not observed preferentially-impaired CK-MM accumulation in any Control-InnCHMFs from 22 patients (children and adults) with a variety of neuromuscular diseases. There was no apparent difference between DMD-InnCMFs and Control InnCHMFs regarding: acceptance of innervation; neuronally-driven, virtually continuous muscle-fiber contractions; characteristic myofiber organization by phase-contrast microscopy, and increased longevity of the innervated fibers.

De novo neuromuscular junction formation on human muscle fibres cultured in monolayer and innervated by foetal rat spinal cord: ultrastructural and ultrastructural--cytochemical studies

Ultrastructural features of neuromuscular junction formation and transverse tubule development were studied utilizing a newly developed model in which human muscle fibres cultured in monolayer are innervated by foetal rat spinal cord with dorsal root ganglia attached. At early innervation (7-10 days), when distinct 'boutons' are contacting muscle fibres, the contacts of nerve terminals with the muscle fibres are, ultrastructurally, superficial and unorganized, and there is no basal lamina-like material between nerve terminals and muscle fibres. A bouton consists, ultrastructurally, of a cluster of small nerve terminals contacting the muscle fibre. At 2-3 weeks of innervation, shallow 'beds' are formed on the muscle fibre just beneath nerve terminals, and occasionally there are irregular and miniscule fragments of basal lamina-like material in the cleft. There is no Schwann cell apposing the nerve terminal at this stage of innervation. After 4-5 weeks of innervation there is more definite basal lamina material in the cleft and suggestive postsynaptic plasmalemmal densities and invaginations. However, there is no Schwann cell apposing the nerve terminal at this stage. At 6-8 weeks of innervation, deep postsynaptic folds are present, a Schwann cell apposes the nerve terminal, and basal lamina surrounds the entire muscle fibre. At all four stages of innervation examined, ultrastructural cytochemistry of alpha-bungarotoxin binding reveals that nicotinic ACh receptors are located exclusively at the neuromuscular junctions. After 1-2 weeks of innervation, very few lanthanum-positive transverse tubules are observed and only in close proximity to the surface membrane. After 3 weeks of innervation, more lanthanum-positive tubules are present, and they are located deeper within the muscle fibre. Five weeks after innervation, somewhat more elaborated tubules (but no lateral sacs) appear, and honeycomb structures are often present. After 6-7 weeks of innervation the tubular system is very elaborate and lateral sacs are present. Hence, this study describes consecutive stages of the formation of neuromuscular junctions and transverse tubules in innervated cultured human muscle, and provides an important basis to which similar studies related to the diseased human muscle can be compared.

Developmental expression of the muscle-specific isozyme of phosphoglycerate mutase in human muscle cultured in monolayer and innervated by fetal rat spinal cord

The electrophoretic pattern of phosphoglycerate mutase of adult innervated normal human muscle is composed predominantly of the muscle-specific isozyme, whereas the electrophoretic pattern of aneurally cultured human muscle is composed only of the brain-specific isozyme. We studied the transition of the isozymes (phosphogluterate mutase) in human muscle cultured in monolayer and innervated for 20 to 83 days by rat embryo spinal cord explants. In this culture system, regions of innervated muscle fibers in close proximity to the ventral part of the spinal cord explant continuously contracted and the contractions were reversibly blocked by 1 mM d-tubocurarine. In those innervated cultured human muscle fibers, the total activity of phosphoglycerate mutase was increased and the muscle-specific isozyme was expressed. The amount of muscle-specific isozyme directly correlated with the duration of innervation. This study demonstrated that expression of the gene for the muscle-specific isozyme of phosphoglycerate mutase in human muscle cultured in monolayer is influenced by de novo innervation.

Expression of muscle-gene-specific isozymes of phosphorylase and creatine kinase in innervated cultured human muscle

Isozymes of creatine kinase and glycogen phosphorylase are excellent markers of skeletal muscle maturation. In adult innervated muscle only the muscle-gene-specific isozymes are present, whereas aneurally cultured human muscle has predominantly the fetal pattern of isozymes. We have studied the isozyme pattern of human muscle cultured in monolayer and innervated by rat embryo spinal cord explants for 20-42 d. In this culture system, large groups of innervated muscle fibers close to the ventral part of the spinal cord explant continuously contracted. The contractions were reversibly blocked by 1 mM d-tubocurarine. In those innervated fibers, the total activity and the muscle-gene-specific isozymes of both enzymes increased significantly. The amount of muscle-gene-specific isozymes directly correlated with the duration of innervation. Control noninnervated muscle fibers from the same dishes as the innervated fibers remained biochemically immature. This study demonstrated that de novo innervation of human muscle cultured in monolayer exerts a time-related maturational influence that is not mediated by a diffusable neural factor.

Myoglobinuria and carnitine palmityltransferase (CPT) deficiency: studies with malonyl-CoA suggest absence of only CPT-II

A 23-year-old man suffered since adolescence from recurrent myoglobinuria. His ketone body production during fasting was normal. Muscle, liver, and platelet carnitine palmityltransferase (CPT) ranged from 4 to 27% of control by isotope exchange and backward assays. Forward CPT activity was 34% of control in liver, whereas in muscle and platelets it was either normal or absent depending on the experimental conditions. CPT residual activity was studied with malonyl-CoA, a physiologic inhibitor of CPT-I (sensitive fraction) in rat liver mitochondria. In our patient, the insensitive fraction was missing in muscle, liver, and platelets, while the sensitive fraction was increased considerably in the same tissues. Similar results were obtained in platelets of two other patients with CPT deficiency. Increased malonyl-CoA sensitive CPT and decreased malonyl-CoA insensitive CPT suggest absence of only the CPT-II isoenzyme in these patients.