A method for measuring the lifetime of chemically and metabolically generated electrophilic species

A method is presented for the characterization of the reaction order and rate constant for chemically and metabolically generated reactive electrophilic intermediates. The procedure employs flow kinetics and trapping of the electrophilic species. Reactive agents or metabolic intermediates are passed through a column containing a bound nucleophilic reagent. The electrophilic species reacts at a characteristic rate while moving through the column at a fixed pH, temperature and rate of flow. The alkylation products formed during this reaction are quantified in individual column segments which correspond to time intervals. This provides data for the calculation of the lifetime of the short-lived species. The method may be used for agents having half-lives of 1 s to 30 min. Metabolic intermediates need not be isolated. Data is presented for the reaction rates of 1-methyl-1-nitrosourea (MNU), 1-methyl-3-nitro-1-nitrosoguanidine (MNNG) and iodomethane. A metabolic activation system is described for the conversion of acetoxymethylmethylnitrosamine (DMN-OAc) to hydroxymethylmethylnitrosamine (DMN-OH) and measurement of the stability of that intermediate. Hydroxymethylmethylnitrosamine was found to have a half-life of 28 s at pH 7.4, 37°C.     

Ball and socket figures between secretory vesicles in mammary epithelial cells

Summary Interaction of adjacent secretory vesicles through ball and socket figures was observed in milk secreting mammary epithelial cells preserved by quick freezing without chemical fixation. Membranes of adjacent vesicles appeared to be fused together. Such vesicle-vesicle interactions have been described in chemically fixed tissues, but it has been argued that these interactions may have been fixation artifacts. Ball and socket figures in quick-frozen cells were smaller than those in chemically fixed cells. However, their existence in cells arrested by quick freezing argues that such vesicle-vesicle interactions occur in living cells.     

Development of the mouse hematopoietic system. II. Estimation of spleen and liver "stem" cell number

Colony-forming cells (CFU), which have the general properties of hemopoietic “stem” cells, appear to be augmented in the mouse fetal liver from 12–18 days gestation and then decrease in the newborn. This finding suggests that few, if any, hemopoietic “stem” cells remain in the adult liver, an organ which appears to be unable to function erythropoietically, even at times of severe crises. In the spleen, and active adult as well as embryonic hematopoietic organ, the total number of CFU increases from 18 days gestation until at least 7 days after birth. Spleen and liver CFU augmentation seems to occur in cojunction with an analogous expansion of non-hematopoietic cells. The data suggests, in fact, that while there is an increase in the total number of liver CFU, there is also a dilution of liver CFU in the total cell population at successively later gestational ages.