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J Childress

Publications and source records attributed to J Childress.

7 recordsLinked to original sources
PubMed1997

Diffraction contrast imaging of extracellular matrix components using zero-loss filtering.

The beta-chitin microfibrils from the deep-sea hydrothermal vent worm Riftia pachyptila were studied in both mature and fresh tubes experimentally obtained. The methods used were electron diffraction and electron diffraction contrast images, in conjunction with an electron-energy filter, operated in the zero-loss mode. In both studied samples, microfibrils are organized in successive layers, inside which they are parallel. However, the fresh tube is less densely packed and diffraction data show that these microfibrils may be in a partially hydrated state. These results indicate that a later step occurs in the compaction of the tube material once it has been extruded. Comparison of filtered and unfiltered diffraction patterns shows that zero-loss filtering significantly improves both working conditions and quality of diffraction recordings.

Actin Cytoskeleton↗
PubMed1997

The effects of exposure to ammonia on ammonia and taurine pools of the symbiotic clam

The nutrition of the gutless clam Solemyareidi is supported by the activity of intracellular chemoautotrophic bacteria housed in its gill filaments. Ammonia (the sum of NH3 and NH4+) is utilized as a nitrogen source by the association and is abundant in the clam's environment. In the present study, clams were exposed to 0.01­1.3mmoll-1 ammonia for 22­23h in the presence of thiosulfate as a sulfur substrate. Ammonia exposure increased the ammonia concentration in the tissue pools of the gill, foot and visceral mass from 0.5 to 2µmolg-1wetmass, without added ammonia, to as much as 12µmolg-1wetmass in the presence of 0.7 and 1.3mmoll-1 external ammonia. Gill tissue ammonia concentrations were consistently higher than those in the foot and visceral mass. The elevation of tissue ammonia concentration compared with the medium may be due in part to an ammonia trapping mechanism resulting from a lower intracellular pH compared with sea water and greater permeability to NH3 compared with NH4+. Rates of ammonia incorporation into organic matter (assimilation) were determined using 15N as a tracer. 15N-labeled ammonia assimilation was higher in gill than in foot and increased as a function of 15N-labeled ammonia concentration in the medium. The size of the free amino acid (FAA) pool in the gill also increased as a function of ammonia concentration in the medium. This entire increase was accounted for by a single amino acid, taurine, which was the predominant FAA in both gill and foot tissue. Aspartate, glutamate, arginine and alanine were also abundant but their levels were not influenced by external ammonia concentration. Ammonia assimilation appeared to occur at rates sufficient to account for the observed increase in taurine level. These findings suggest that taurine is a major product of ammonia assimilation.

Journal Article↗
PubMed1997

Inorganic carbon acquisition by the hydrothermal vent tubeworm Riftia pachyptila depends upon high external PCO2 and upon proton-equivalent ion transport by the worm

Riftia pachyptila is the most conspicuous organism living at deep sea hydrothermal vents along the East Pacific Rise. To support its large size and high growth rates, this invertebrate relies exclusively upon internal chemosynthetic bacterial symbionts. The animal must supply inorganic carbon at high rates to the bacteria, which are far removed from the external medium. We found substantial differences in body fluid total inorganic carbon (CO2) both within and between vent sites when comparing freshly captured worms from a variety of places. However, the primary influence on body fluid CO2 was the chemical characteristics of the site from which the worms were collected. Studies on tubeworms, both freshly captured and maintained in captivity, demonstrate that the acquisition of inorganic carbon is apparently limited by the availability of CO2, as opposed to bicarbonate, and thus appears to be accomplished via diffusion of CO2 into the plume, rather than by mediated transport of bicarbonate. The greatly elevated PCO2 measured at the vent sites (up to 12.6 kPa around the tubeworms), which is a result of low environmental pH (as low as 5.6 around the tubeworms), and elevated CO2 (as high as 7.1 mmol l-1 around the tubes) speeds this diffusion. Moreover, despite large and variable amounts of internal CO2, these worms maintain their extracellular fluid pH stable, and alkaline, in comparison with the environment. The maintenance of this alkaline pH acts to concentrate inorganic carbon into extracellular fluids. Exposure to N-ethylmaleimide, a non-specific H+-ATPase inhibitor, appeared to stop this process, resulting in a decline in extracellular pH and CO2. We hypothesize that the worms maintain their extracellular pH by active proton-equivalent ion transport via high concentrations of H+-ATPases. Thus, Riftia pachyptila is able to support its symbionts' large demand for inorganic carbon owing to the elevated PCO2 in the vent environment and because of its ability to control its extracellular pH in the presence of large inward CO2 fluxes.

Journal Article↗
PubMed1996

Ambulatory infusional cancer chemotherapy: nursing role in patient management. The Cancer Center of Boston.

The role of nursing in infusional cancer chemotherapy (ICC) may vary depending on the practice setting. Nurses in free-standing centers and office practices perform many duties that nurses in other facilities may not, because of the lack of many of the supports that benefit hospitals with their multidepartmental and hierarchical structures. Nurses function collaboratively with physicians in the planning and the implementation of patient treatment. Patient-related nursing responsibilities include patient/family education, drug preparation and administration, patient assessment for treatment toxicity, recognition and management of complications related to the catheter or infusion device, and telephone triage. Other duties more removed from patient care might include inventory management, research data collection and management, quality assurance and improvement, compliance with regulatory issues, and a myriad of other responsibilities. The transition of patient care to the outpatient setting has broadened the scope of nursing to include nonpatient care responsibilities due to financial constraints brought about by health care reform, changes in reimbursement patterns, and overhead required to maintain and deliver quality patient care. As a result of nursing responsibilities, it becomes paramount that the aforementioned constructs for program support are in place and that all nurses are consistently trained and have a template to follow for patient treatment and management. Nursing ability to perform patient-related tasks should be proven by formal written and practical competencies repeated annually and as procedural changes are implemented. The paragraphs to follow suggest nursing management of patients receiving ICC using a model developed at The Cancer Center of Boston (TCC).

Ambulatory Care↗
PubMed1996

Surveillance of the patient receiving infusional cancer chemotherapy: nursing role in recognition and management of catheter-related complications. The Cancer Center of Boston.

Surveillance of the patient on infusional cancer chemotherapy (ICC) is paramount to patient safety. Key to this issue is diligence in monitoring for complications of infusion catheters. Nursing knowledge and awareness are essential for the early detection of such complications. The following is a composite of the manifestations of commonly experienced catheter-related complications. The incidence, detection and management issues are presented from the perspective of 15 years experience with ICC at The Cancer Center of Boston (TCC).

Ambulatory Care↗
PubMed1986

Patterns of pigmentation in the eye lens of the deep-sea hatchetfish, Argyropelecus affinis Garman.

The present study is a morphological, biochemical and spectrophotometric characterization of the eye lens pigmentation in 45 specimens (11-88 mm in standard length) of the deep-sea hatchetfish, Argyropelecus affinis (Stomiiformes: Sternoptychidae). For comparison, we also examined available lenses of other members of the family Sternoptychidae, including three other species of the genus Argyropelecus, and two species of the genus Sternoptyx. Lens pigmentation was observed in all specimens of Argyropelecus spp. larger than about 36 mm in standard length, but was absent in all Argyropelecus spp. individuals less than 36 mm. However, lens pigmentation was not observed in Sternoptyx specimens of any size. Detailed studies of A. affinis indicated that at 36 mm the nascent lens fiber cells, which are continually laid down over preexisting, unpigmented cells, begin incorporating pigment, and the pigment concentration increases steadily as pigmented cells are added during lens growth. Spectrophotometric and biochemical data suggested that the pigment is a carotenoprotein complex, the carotenoid-like chromophore being strongly associated with a specific soluble lens protein, alpha crystallin. While the lens coloration in these fishes is age-related, analyses of the retinal visual pigment revealed no concomitant age-related change in the peak wavelength of retinal sensitivity in these fishes. Our data on the spectral absorbance of the lens and visual pigment of these fishes suggest that the lens pigmentation acts as a short-wave filter to improve acuity of the visual system.

Animals↗