Processing of Digestive Vacuoles in Tetrahymena and the Effects of Dichloroisoproterenol1

The digestive-lysosomai system in Telrahymena has been extensively studied; however, the various vacuole stages and the existence of a required processing period prior to defecation have not been clearly denned, in this study the presence of such a required processing period and the rate of DV defecation in Tetrahymena thermophila were determined. Like the cycle in Paramecium. a digestive cycle in Tetrahymena consisted of two periods: the processing period was 45 min and the defecation period was ?2 h, making the complete cycle ?3 h. During the defecation period vacuole egestion followed the kinetics of a first-order rate reaction and had a rate constant of 0.0187/min and a t1/2 of 37 min (82 min into the cycle). Using the naphthol AS-TR phosphate-hexazotized rosanilin method to visualize acid phosphatase activity at the light microscopic level, DVs became positive beginning at 10 min. The number of positive DVs increased to a maximum of 13% when DVs were 20-min old and declined to 5-7% beyond 30 min. Although dichloroisoproterenol (DCI) has been reported by others to stimulate vacuole defecation, we found it inhibited the defecation rate. The extent of inhibition depended on the age of the DVs when exposed to DCI. Vacuole formation was completely blocked in cells pre-exposed to 40 μ DCI for only 10 min; however, upon further exposure, cells could recover from this inhibition. The time required for complete recovery increased with increasing DCI concentrations. If DCI was given to cells simultaneously with latex beads, it was found to exert a dose-dependent inhibitory effect on DV formation. These results showed the heterophagic pathway of the digestive-lysosomal system in Telrahymena to be similar to that of Paramecium, though it was less efficient in the former cell.     

Accelerated Search Kinetics Mediated by Redox Reactions of DNA Repair Enzymes

A charge transport (CT) mechanism has been proposed in several articles to explain the localization of base excision repair (BER) enzymes to lesions on DNA. The CT mechanism relies on redox reactions of iron-sulfur cofactors that modify the enzyme's binding affinity. These redox reactions are mediated by the DNA strand and involve the exchange of electrons between BER enzymes along DNA. We propose a mathematical model that incorporates enzyme binding/unbinding, electron transport, and enzyme diffusion along DNA. Analysis of our model within a range of parameter values suggests that the redox reactions can increase desorption of BER enzymes not already bound to lesions, allowing the enzymes to be recycled—thus accelerating the overall search process. This acceleration mechanism is most effective when enzyme copy numbers and enzyme diffusivity along the DNA are small. Under such conditions, we find that CT BER enzymes find their targets more quickly than simple passive enzymes that simply attach to the DNA without desorbing.     

Factors associated with difference in prevalence of asthma in children from three cities in China: multicentre epidemiological survey

Objective To determine the factors associated with difference in prevalence of asthma in children in different regions of China.Design Multicentre epidemiological survey.Setting Three cities in China.Participants 10 902 schoolchildren aged 10 years.Main outcome measures Asthma and atopic symptoms, atopic sensitisation, and early and current exposure to environmental factors.Results Children from Hong Kong had a significantly higher prevalence of wheeze in the past year than those from Guangzhou and Beijing (odds ratio 1.64, 95% confidence interval 1.35 to 1.99). Factors during the first year of life and currently that were significantly associated with wheeze were cooking with gas (odds ratio 2.04, 1.34 to 3.13), foam pillows (2.58, 1.66 to 3.99), and damp housing (1.89, 1.26 to 2.83). Factors protecting against wheeze were cotton quilts and the consumption of fruit and raw vegetables.Conclusion Environmental factors and diet may explain the differences in prevalence of asthma between children living in different regions of China.