Biomedical subjects

M Wasserman

Publications and source records attributed to M Wasserman.

62 records · Page 4Linked to original sources

PubMedDate not supplied

Evolution of the mojavensis cluster of cactophilic Drosophila with descriptions of two new species.

The mojavensis cluster of the repleta species group of Drosophila (Drosophilidae: Diptera) consists of three species. One is newly described as D. navojoa. A second species, described here as D. arizonae, replaces D. arizonensis, which has become a junior subjective synonym for D. mojavensis, the third species in the cluster. A phylogeny of the three species is presented, based on chromosomal inversions, morphology, and the ability to produce hybrids. Breakage points are assigned for all inversions, and male genitalia are figured; 186 crosses were made from 225 possible combinations among 15 geographic strains from the southwestern United States, Mexico, and Guatemala. It is confirmed that D. mojavensis and D. arizonae are very closely related and shown that D. navojoa is more distantly related in regard to all criteria. This relationship is supported by the geographical positions of the ancestral gene sequences in each species, which show a sequential northwest movement (D. navojoa----D. arizonae----D. mojavensis) from southern Mexico to southern California and northern Arizona. The relationship is also supported by the fact that D. navojoa breeds in Opuntia cactus, an ancestral behavior, whereas the other two species breed chiefly in Stenocereus cacti, a derived behavior. The possible role of this host plant shift in speciation is discussed.

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PubMedDate not supplied

Plasmodium falciparum: increased and multiple invasion during short periods of time.

We describe how to obtain an increased merozoite invasion of Plasmodium falciparum into human erythrocytes during short periods of time. Using this procedure, infected erythrocytes show multiple invasions (2-4 merozoites per erythrocyte), amplifying, several times, the effects of parasite entry into host cells. The procedure yields synchronous cultures (2-h age range) with parasitemia as high as 15%. It is possible to reach parasitemia of 50% or higher allowing for a 6-h invasion period.

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PubMedDate not supplied

Effect of low temperature on the in vitro growth of Plasmodium falciparum.

The effect of low incubation temperature on synchronized cultures of Plasmodium falciparum was studied. Young trophozoites that were maintained at 28 degrees C matured slowly and invaded poorly. Growth seemed to arrest when parasites reached a maturation equivalent to 30 h, although they reestablished their growth normally when returned to 37 degrees C. On the other hand, 36-h synchronized parasites that were transferred to 28 degrees C completed their cell cycle with a 12-16 h delay, but without changes in the parasite as seen by light microscopy and without a diminution in the efficiency of the invasion or in the incorporation of 35S-methionine. These results might be useful for obtaining parasites at defined stages of development at the desired time.

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PubMedDate not supplied

Detection of Genomic Polymorphism in Plasmodium falciparum using an arbitrarily primed PCR assay.

Modifications of the arbitrarily primed polymerase chain reaction assay (i.e. a low annealing temperature and a very slow increase in the temperature during the elongation steps during the amplification cycles) allowed it to be used with the AT-rich Plasmodium falciparum DNA. The analysis of the products by polyacrylamide-urea gels, after silver staining, resulted in high resolution and sensitivity. Eighteen single and six combined pairs of arbitrary primers were tested. Two produced polymorphic patterns complex enough to differentiate between close Colombian isolates in a single assay. This method may be useful in studying the distribution and migration of strains in endemic areas, and for identifying intralaboratory cross-contamination of cultures.

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PubMedDate not supplied

Two types of growth hormone rhythm in boys with constitutional short stature.

The relationship between temporal and quantitative changes in pulsatile growth hormone (GH) secretion and growth of constitutionally short children (CSS) was studied in 19 prepubertal boys and 4 with early adrenarche aged 7.8 to 14 years. Continuous plasma GH monitoring was performed at 30 minutes intervals during 24 hours. The data were analysed by single and serial best fit (BFT) cosinor analysis for rhythm parameters and the Pulsar peak detection program for determining pulsatile properties. The pulsatile patterns were expressed in mean GH concentration, area under the curve, mean pulse area and maximal pulse height but not in the number of pulses. Thirteen out of 23 patterns exhibited significant 24-h compatible rhythms. The studied cohort was divided into two groups, those who exhibited the 24-h circadian rhythm (CIR) and those who lacked it (NCIR). Ultradian 2.5-4 h rhythms were observed in all patients. The NCIR children were significantly shorter than the CIR group (p = 0.017). The CIR boys secreted a significantly higher (p = 0.01) amount of GH during the 24-h span, most of which was during sleep. Our data indicate that the magnitude of pulses rather than their number is responsible for the quantitative differences observed between the two groups of boys with CSS. It is suggested that a lack of 24-h rhythmicity and the associated reduced nocturnal pulsatility play a role in the manifestation of short stature.

Activity Cycles↗

PubMedDate not supplied

Increase of a calcium independent transglutaminase activity in the erythrocyte during the infection with Plasmodium falciparum.

We have studied the activity of a calcium dependent transglutaminase (EC 2.3.2.13) during the growth of the parasite Plasmodium falciparum inside the infected human erythrocyte. There is only one detectable transglutaminase in the two-cell-system, and its origin is erythrocytic. No activity was detected in preparations of the parasite devoid of erythrocyte cytoplasm. The Michaelis Menten constants (Km) of the enzyme for the substrates N'N' dimethylcaseine and putrescine were undistinguishable whether the cell extracts used in their determination were obtained from normal or from infected red cells. The total activity of transglutaminase in stringently synchronized cultures, measured at 0.5 mM Ca2+, decreased with the maturation of the parasite. However, a fraction which became irreversibly activated and independent of calcium concentration was detected. The proportion of this fraction grew with maturation; it represented only 20% of the activity in 20 hr-old-trophozoites while in 48-hr-schizonts it was more than 85% of the total activity. The activation of this fraction of transglutaminase did not depend on an increase in the erythrocyte cytoplasmic calcium, since most of the calcium was shown to be located in the parasite.

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PubMedDate not supplied

Isolation and identification of actin-binding proteins in Plasmodium falciparum by affinity chromatography.

The invasion of the erythrocyte by Plasmodium falciparum depends on the ability of the merozoite to move through the membrane invagination. This ability is probably mediated by actin dependent motors. Using affinity columns with G-actin and F-actin we isolated actin binding proteins from the parasite. By immunoblotting and immunoprecipitation with specific antibodies we identified the presence of tropomyosin, myosin, a-actinin, and two different actins in the eluate corresponding to F-actin binding proteins. In addition to these, a 240-260 kDa doublet, different in size from the erythrocyte spectrin, reacted with an antibody against human spectrin. All the above mentioned proteins were metabolically radiolabeled when the parasite was cultured with 35S-methionine. The presence of these proteins in P. falciparum is indicative of a complex cytoskeleton and supports the proposed role for an actin-myosin motor during invasion.

Actins↗

PubMedDate not supplied

Differential effects of leukotrienes C4, D4, and E4 in the pulmonary and systemic vasculature of sheep.

We investigated the comparative direct and cyclooxygenase-mediated effects of the constituents of slow-reacting substance of anaphylaxis (SRS-A), i.e., leukotriene C4 (LTC4), leukotriene D4 (LTD4) and leukotriene E4 (LTE4) on pulmonary and systemic haemodynamics of sheep. In 20 conscious sheep, measurements of pulmonary vascular resistance (Rpv) and systemic vascular resistance (Rsv) were obtained before and after a rapid intravenous injection of LTC4 (0.1 micrograms X kg-1), LTD4 (0.1 micrograms X kg-1) and LTE4 (1 microgram X kg-1). The same protocol was carried out after pretreatment with the leukotriene antagonist FPL-57231 or the cyclooxygenase inhibitor indomethacin. LTD4 increased mean Rpv to 421% of baseline (p less than 0.001) and had a biphasic effect on mean Rsv, which, following an initial decrease of 18% (p less than 0.05), increased to 143% of baseline (p less than 0.05). LTC4 and LTE4 had no significant effects on Rpv, while they increased mean Rsv to 144% and 143% of baseline, respectively (p less than 0.05). This effect was not preceded by a decrease in Rsv. FPL-57231 completely blocked the effects of LTC4, LTD4 and LTE4 on Rsv, and of LTD4 on Rpv. Indomethacin had no effect on LTC4, LTD4 and LTE4-induced increases in mean Rsv, while it prevented the LTD4-induced initial decrease in mean Rsv. Indomethacin also prevented the LTD4-induced increase in Rpv. A dose-response curve (0.05, 0.1, 0.5 and 1 microgram X kg-1) demonstrated that in raising Rsv, LTE4 was approximately 10 times less potent than LTC4 and LTD4.(ABSTRACT TRUNCATED AT 250 WORDS)

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