The effects of halothane on the DNase I activity in an isolated enzyme preparation and in the DNase I-G actin complex

The effects of halothane on the DNase I activity in an isolated enzyme preparation and in a DNase I-globular (G) actin complex was investigated. DNase I, DNase I-G actin complexes and G actin were exposed to various (0.2–4.0 vol./%) halothane concentrations for 3 h. Thereafter, DNase I was mixed with a DNA solution and the extinction of the acid soluble supernatant of the DNase I assay was determined as a measure of DNase I activity. After 10 min of halothane exposure the DNase I activity is inhibited in direct proportion to halothane concentrations between 0.6 and 4.0 vol/%. After 10 min halothane activates inactive DNase I by inhibiting G actin, an inhibitor of DNase I. G actin, exposed to halothane, does not inhibit the activity of DNase I. The results suggest a mechanism by which halothane may contribute to chromosomal defects and disturbances of DNA metabolism in cells.     

Development and Maintenance of the Neuronal Cytoskeleton in Aggregated Cell Cultures of Fetal Rat Telencephalon and Influence of Elevated K+ Concentrations

Serum-free aggregating cell cultures of fetal rat telencephalon were examined by biochemical and immunocytochemical methods for their development-dependent expression of several cytoskeletal proteins, including the heavy- and medium-sized neurofilament subunits (H-NF and M-NF, respectively); brain spectrin; synapsin I; beta-tubulin; and the microtubule-associated proteins (MAPs) 1, 2, and 5 and tau protein. It was found that with time in culture the levels of most of these cytoskeletal proteins increased greatly, with the exceptions of the particular beta-tubulin form studied, which remained unchanged, and MAP 5, which greatly decreased. Among the neurofilament proteins, expression of M-NF preceded that of H-NF, with the latter being detectable only after approximately 3 weeks in culture. Furthermore, MAP 2 and tau protein showed a development-dependent change in expression from the juvenile toward the adult form. The comparison of these developmental changes in cytoskeletal protein levels with those observed in rat brain tissue revealed that protein expression in aggregate cultures is nearly identical to that in vivo during maturation of the neuronal cytoskeleton. Aggregate cultures deprived of glial cells, i.e., neuron-enriched cultures prepared by treating early cultures with the antimitotic drug cytosine arabinoside, exhibited pronounced deficits in M-NF, H-NF, MAP 2, MAP 1, synapsin I, and brain spectrin, with increased levels of a 145-kDa brain spectrin breakdown product. These adverse effects of glial cell deprivation could be reversed by the maintenance of neuron-enriched cultures at elevated concentrations of KCl (30 mM). This chronic treatment had to be started at an early developmental stage to be effective, a finding suggesting that sustained depolarization by KCl is able to enhance the developmental expression and maturation of the neuronal cytoskeleton.