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D Osborn

Publications and source records attributed to D Osborn.

52 records · Page 3Linked to original sources
PubMed1977

Measurements of contraction latencies to mechanical and electrical stimulation of the protozoan, Spirostomum ambiguum.

Measurements made on contraction latencies in Spirostomun suggest that mechanical stimulation causes contractions to be initiated by the release of small amounts of calcium from a store tightly coupled to the contractile apparatus. Contraction to electrical stimulation appears to result from the gross electrophoretic mobilization of large amounts of calcium from a loosely coupled store. Contraction latencies to mechanical stimulation were three milliseconds and were independent of stimulus strength, previous stimulation, and contraction probability. For 0.5-millisecond biphasic electrical stimulation the contraction latencies varied widely. Latencies to initial contractions were dependent on stimulus strength: from 1.0 milliseconds for a stimulus that caused a 100% probability of contraction to 2.0 milliseconds for a stimulus that caused a 10% probability of contraction. Latencies of contraction to electrical stimulation were also dependent upon previous stimulation, lengthening to over 300 milliseconds after ten minutes of stimulation. Initial contraction latencies were not affected by previous stimulation to the other (electrical or mechanical) stimulus modality. Repeated electrical stimulation also reduced the animal's resting length and slowed the rate of post contraction re-extension, whereas mechanical stimulation did not have these effects.

Animals↗
PubMed1977

Electron microbeam analysis of calcium distribution in the ciliated protozoan, Spirostomum ambiguum.

Electron microprobe analyses of calcium distribution in the ciliated protozoan, Spirostomum ambiguum, indicated several calcium rich sites. One site was an endoplasmic distribution of calcium coincident with phosphorus which corroborates previous findings of hydroxyapatite deposits within Spirostomum. These apatite deposits were distributed throughout the endoplasm, but not within the nuclei or the contractile vacuole. Calcium was also detected within the cortical region. Cortical calcium was in greater concentration in the anterior portion of the organism and decreased towards the posterior end (region containing the contractile vacuole). Phosphorus and potassium were also detected as gradients from the anterior end, whereas magnesium was detected in the same density throughout the cortical region. Line scans of cortical regions suggested (1) distributions of calcium within mitochondria and/or vesicles, and (2) calcium associated with bundles of microfilaments.

Animals↗
PubMedDate not supplied

Cadmium and mercury nephrotoxicity.

Despite increasing attempts to control environmental pollution, changes in the distribution and bioavailability of toxic metals like mercury and cadmium are still occurring. Apart from natural processes, other contributory factors include the gradual spread of industrialization, the use of sewage sludge as a fertilizer and the acidification of Northern Hemisphere groundwater. Animals (including man and domestic varieties) can accumulate harmful concentrations of toxic metals. We therefore looked for damage to the kidneys in seabirds contaminated with mercury and cadmium and made comparisons with kidneys from three other groups of animals: seabirds from an uncontaminated colony, metal-dosed birds and metal-dosed mice. We report here that, comparing all these groups of animals, individuals with comparatively high levels of metals had nephrotoxic lesions of a similar type and severity. Moreover, the metal concentrations at which damage began and at which biochemical changes could be detected were below those presently considered as relatively safe for humans by the World Health Organization.

Animals↗