Gas mixing in the airways of dog lungs during high-frequency ventilation

Washout of insoluble inert test gases of different diffusivity (He and SF6 or He and Ar) from dog lungs was studied during high-frequency ventilation (HFV). Test gas equilibrium and subsequent washout were performed with HFV, succeeding measurements being performed at different stroke volumes (1.5-2.5 ml/kg body wt), oscillation frequencies (10-30 Hz), and with different lung volumes (32-74 ml X kg-1). Test gas concentrations were continuously measured by a mass spectrometer. The time course of washout could be described as the sum of two exponentials. There were no consistent differences in the time courses of washout between He and SF6 or between He and Ar. It is concluded that gas mixing in the airways during HFV is not significantly limited by diffusion, and this is suggested to apply during HFV to steady-state transport of respiratory gases (e.g., O2 and CO2) as well as to the transient state of inert gas washout.     

Saturated Fatty Acid Mutant of Saccharomyces cerevisiae with an Intact Fatty Acid Synthetase

To determine directly the effects of streptomycin on translational fidelity in intact cells, we studied the synthesis of beta-galactosidase and of the coat protein of bacteriophage R17 in an Escherichia coli mutant in which the bactericidal effects of streptomycin are delayed. After the addition of streptomycin to exponentially growing mutant cells, protein synthesis continues at an undiminished rate for approximately an hour; however, as measured by enzyme assays, little functional protein is produced. Serological assays designed to detect beta-galactosidase and bacteriophage R17 coat protein show that substantial amounts of the protein synthesized can react with antisera prepared against active beta-galactosidase and phage R17, indicating the aberrance of the protein produced in the presence of the antibiotic. The polypeptides synthesized in the presence of streptomycin are degraded in the cell to a much greater extent than protein synthesized in the absence of the antibiotic. The proteolytic attack on this protein is not affected by inhibitors of serine proteases, suggesting that enzymes other than those involved in "normal turnover" of cellular protein are responsible. In this strain, certain of the multiple effects of streptomycin are separated in time and the production of abnormal protein (enzymatically inactive and susceptible to proteolytic attack) could be studied in the absence of the lethal effect of the drug.