Biomedical subjects

M Womack

Publications and source records attributed to M Womack.

At least 19 recordsLinked to original sources

PubMed2001

Outgassing behavior and composition of comet C/1999 S4 (LINEAR) during its disruption.

The gas activity of comet C/1999 S4 (LINEAR) was monitored at radio wavelengths during its disruption. A runaway fragmentation of the nucleus may have begun around 18 July 2000 and proceeded until 23 July. The mass in small icy debris (</=30-centimeter radius) was comparable to the mass in the large fragments seen in optical images. The mass budget after breakup suggests a small nucleus ( approximately 100- to 300-meter radius) that had been losing debris for weeks. The HNC, H2CO, H2S, and CS abundances relative to H2O measured during breakup are consistent with those obtained in other comets. However, a deficiency in CH3OH and CO is observed.

Journal Article↗

PubMed1999

A role for the clathrin assembly domain of AP180 in synaptic vesicle endocytosis.

We have used the squid giant synapse to determine whether clathrin assembly by AP180 is important for synaptic vesicle endocytosis. The squid homolog of AP180 encodes a 751 amino acid protein with 40% sequence identity to mouse AP180. Alignment of squid AP180 with other AP180 homologs shows that amino acid identity was highest in the N-terminal inositide-binding domain of the protein and weakest in the C-terminal clathrin assembly domain. Recombinant squid AP180 was able to assemble clathrin in vitro, suggesting a conserved three-dimensional structure that mediates clathrin assembly despite the divergent primary sequence of the C-terminal domain. Microinjection of the C-terminal domains of either mouse or squid AP180 into the giant presynaptic terminal of squid enhanced synaptic transmission. Conversely, a peptide from the C-terminal domain of squid AP180 that inhibited clathrin assembly in vitro completely blocked synaptic transmission when it was injected into the giant presynaptic terminal. This inhibitory effect occurred over a time scale of minutes when the synapse was stimulated at low (0.03 Hz), physiological rates. Electron microscopic analysis revealed several structural changes consistent with the inhibition of synaptic vesicle endocytosis; peptide-injected terminals had far fewer synaptic vesicles, were depleted of coated vesicles, and had a larger plasma membrane perimeter than terminals injected with control solutions. In addition, the remaining synaptic vesicles were significantly larger in diameter. We conclude that the clathrin assembly domain of AP180 is important for synaptic vesicle recycling at physiological rates of activity and that assembly of clathrin by AP180 is necessary for maintaining a pool of releasable synaptic vesicles.

Adaptor Proteins, Vesicular Transport↗

PubMed1998

Elevated intracellular calcium levels in cerebellar granule neurons of weaver mice.

Weaver mice carry a mutation in the pore domain of the Girk2 (Kcnj6) gene. The mutation causes GIRK2 containing channels to lose ion selectivity and to become constitutively active. It is not known how this alteration in ion channel activity causes in cerebellar granule cells the defects in neurite extension, cell migration and induction of cell death that are characteristic of weaver mice. One possibility is that the mutation causes an inability to regulate intracellular calcium levels properly. We tested this hypothesis by measuring intracellular calcium levels in granule cells and Purkinje cells in slices from the cerebellum of weaver mice. We report here that weaver mice have increases in resting calcium levels in their granule cells, which may account for the multiple effects of the weaver mutation upon these cells.

Animals↗

PubMed1994

A randomized, prospective trial comparing amoxicillin and erythromycin for the treatment of Chlamydia trachomatis in pregnancy.

OBJECTIVE: Our purpose was to evaluate the efficacy of amoxicillin as an alternative therapy to erythromycin for the treatment of cervical chlamydial infections during pregnancy. STUDY DESIGN: A randomized, prospective trial of two treatment regimens for Chlamydia trachomatis was performed in a cohort of pregnant women enrolled for care in an inner-city, university-based prenatal clinic, with an alternate-therapy crossover arm for primary treatment failures. Pregnant women diagnosed with chlamydial infection by McCoy cell culture of cervical swabs were assigned to receive either 500 mg of amoxicillin three times daily or 500 mg of erythromycin four times daily for 7 days. Patients' partners were treated with doxycycline. Compliance information was obtained by a standardized questionnaire at a posttherapy follow-up visit. Patients with positive follow-up cultures were crossed over into the alternate treatment arm and recultured at a later visit. RESULTS: During the study period 74 women consented to participate in this trial; 36 were treated with amoxicillin and 38 with erythromycin. Initial cure rates of 82.3% (28/34) for the amoxicillin group and 84.6% (27/32) for erythromycin were obtained before crossover (p = 0.91); four patients in each group were lost to follow-up. Overall cure rates after crossover were 84.6% (33/39) for amoxicillin and 84.2% (32/38) for erythromycin (p = 0.83). In the amoxicillin group 12.8% of patients reported side effects compared with 31.6% treated with erythromycin (p = 0.09), although seven erythromycin-treated patients compared with none of those in the amoxicillin arm stopped therapy because of side effects (p = 0.02). CONCLUSION: Amoxicillin offers a reasonable alternative to erythromycin for the treatment of Chlamydia trachomatis in pregnancy, on the basis of both cure rates and patient compliance.

Amoxicillin↗

PubMed1979

Obligatory urinary and fecal nitrogen losses in young women, older men, and young men and the factorial estimation of adult human protein requirements.

Obligatory urinary and fecal nitrogen losses and urinary urea nitrogen and creatinine excretion levels were determined in 11 young women (four of whom used oral contraceptives), eight older men, and five young men. Values for obligatory nitrogen losses in the young women who did not use oral contraceptives were similar to those observed previously in young women and lower than those reported for young men. Our values for older men were lower than previously reported values for obligatory losses observed in young and elderly men, but similar to previously reported values for young women and to values for our women who did not use oral contraceptives. The four oral contraceptive users had significantly higher levels of total urinary and fecal obligatory nitrogen losses than the nonusers in our study. When values from our study and values from other recent studies are considered, variations in obligatory nitrogen losses appear to be larger among individuals within an age-sex group than the observed differences between groups. When the intakes of protein recommended as safe by the Food aculated from obligatory nitrogen losses per se, the recommended levels appear to be only marginally adequate.

Adult↗

PubMed1979

Percutaneous connections in man.

Neuroprostheses research provides on application of percutaneous access. We have investigated a number of clinical situations requiring chronic percutaneous transmission of either fluid or electricity in man to explore other uses. Selection criteria for new models include the following considerations: 1) it should allow use of a skull mounted pedestal; 2) it should offer the potential of benefit to the patient with minimal extra risks; 3) it should be a common enough problem to provide sufficient clinical material; and 4) it should not require major new developments of technology. Other potential uses include the artifical pancreas, artificial heart, and hyperalimentation. With some modification, it might be possible to provide access to devices located in the chest via the jugular vein. Similarly, other uses for this percutaneous device warrant investigation. Our twenty man-years of experience with the device indicates that it provides successful chronic access when used with appropriate skill.

Animals↗

PubMed1977

Plasma free amino acid levels in human subjects after meals containing lactalbumin, heated lactalbumin, or no protein.

Plasma free amino acids were measured in six adult human subjects at four consecutive 1/2 hr intervals following meals containing either 50 g lactalbumin, 50 g heated lactalbumin, or no protein. After the lactalbumin meal, all essential and several nonessential amino acids increased in the plasma. After the heated lactalbumin meal, these increases were either much less or did not appear. Following the no protein meal all measured plasma amino acids fell. The absence of a response to the heated lactalbumin meal was considered to be related to a drop in digestibility of heated lactalbumin as measured in rats.

Amino Acids↗

PubMed1977

Adaptations to endurance training at three intensities of exercise.

This study was undertaken to investigate the influence of exercise intensity (running speed) on a number of alterations that are known to occur with exercise training. Rats were trained on three treadmill running schedules: 20 m/min, 27 m/min, and 35 m/min for 1 h/day. After 6 wk, lean body mass and body fat content were decreased to the same extent in all three trained groups. Thus, exercise appears to lower body fat by some mechanism that is not related to the amount of energy expended during exercise. Heart and adrenal gland weight-to-lean body mass ratios were increased by training. Heart weight-to-lean body mass ratio increased with increasing intensity of exercise but the adrenal weight-to-lean body mass ratio was independent of exercise intensity. Training increased muscle succinate dehydrogenase activity to the same extent in all three trained groups which suggests that the adaptation in respiratory capacity is not altered greatly by the intensity of training.

Adaptation, Physiological↗

PubMed1972