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Biomedical subjects

J F Wheldrake

Publications and source records attributed to J F Wheldrake.

At least 37 records · Page 2Linked to original sources
PubMed1986

Sulphation and the vegetative growth of Dictyostelium discoideum.

The utilization of [35S]sulphate by bacterially grown amoebae of Dictyostelium discoideum strain NP73 was examined in this study. During vegetative growth the sulphation of at least ten macromolecules was observed. These macromolecules had molecular masses less than 66 kDa and isoelectric points below 5. Simple tests indicated that the sulphate linkage was periodate-sensitive but not acid-labile which implied that carbohydrate moieties, rather than tyrosine residues, were sulphated. Pulse-chase experiments indicated that the sulphated macromolecules were extremely stable during vegetative growth, but that secretion occurred on starvation, resulting in the loss of the sulphated macromolecules to the extracellular medium. Incorporation of [35S]sulphate into these macromolecules by amoebae declined rapidly within 2 h of starvation on membrane filters. In contrast, incorporation by amoebae starving in suspension culture continued for 6-8 h. Similar patterns of [35S]sulphate incorporation were observed for two other strains of D. discoideum (strains AX2 and NC4) and for Polysphondylium violaceum. Since in a previous study it was shown that the sulphation inhibitor, sodium selenate, arrests the growth of D. discoideum [Davis, S.J. & Wheldrake, J.F. (1985) FEMS Micro Lett. 30, 353-358], it is suggested that the sulphation of these macromolecules is necessary for the vegetative growth of D. discoideum.

Dictyostelium↗
PubMed1982

Cardiovascular function during treadmill exercise in the turkey.

1. Heart rate, arterial pressure and blood lactate levels were measured in turkeys over a range of running speeds on a treadmill. 2. Heart rates showed a hyperbolic increase with speed to a level approximately twice that recorded at rest. Arterial pressures were found to be lower than those previously reported for the turkey. During severe exercise, the mean value increased 37% above the resting level. 3. Blood lactate levels were greater at increased work loads, but after an initial rise, the levels remained steady during locomotion. 4. At rest, heart rate increased about 46% following parasympathetic blockade and decreased 19% with sympathetic blockade. During locomotion, parasympathetic tone is minimal. 5. In turkeys free of parasympathetic and beta-adrenergic influences, heart rate still increased at the highest running speed. Neither lactate nor ionotrophic effects appear to cause this increase.

Animals↗
PubMed1982

Skin carcinogenesis and promoter binding characteristics in different mouse strains.

The sensitivity of various mouse strains to skin carcinogenesis has been investigated in two ways; (i) by comparing carcinogenesis induced by treatments involving both the application of tumour promoters and the application of single or multiple doses of a carcinogen, and (ii) by comparing the binding characteristics of the tumour promoter [3H]phorbol-12,13-dibutyrate to particulate skin preparations. The mouse strains tested were Swiss albino, Balb/c, C3H, LACA and AKR/J. Although some differences were apparent, Swiss albino, LACA and C3H mice were generally sensitive to skin carcinogenesis by both benzo[a]pyrene and 7,12-dimethylbenz[a]anthracene, either with or without promotion with croton oil. AKR/J mice were sensitive to both carcinogens with promotion but relatively insensitive in the absence of promotion. Balb/c mice had low sensitivity except when exposed to repeated low doses of benzo[a]pyrene. The [3H]phorbol-12,13-dibutyrate binding characteristics of particulate skin preparations from all strains were indistinguishable.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1980

Effects of saline exposure on the response of toad bladder (Bufo marinus) to aldosterone.

1. The short-circuit current response of toad bladders to high concentrations of aldosterone (2 x 10(-7) M) has been investigated following saline exposure of toads. 2. Limited saline exposure appears to enhance the aldosterone-stimulated response. 3. Additional saline exposure results in a reduced aldosterone response. 4. Overnight pre-incubation of isolated bladders proved a better pretreatment condition for study of an aldosterone short-circuit current response. 5. Plasma aldosterone concentrations and studies of [3H]aldosterone binding in the bladders have failed to demonstrate significant effects of saline exposure on endogenous aldosterone concentrations.

Aldosterone↗
PubMed1979

Mixed-function oxidase activity in a desert rodent, Notomys alexis.

1. The levels of enzymes associated with the hapatic mixed-function oxidase system, and the rates of oxidation of three substrates, are compared in the desert rodent, Notomys alexis, and the laboratory mouse, Mus musculus. 2. In general, the activity of the mixed-function oxidase system in Notomys alexis is greater than in Mus musculus. 3. Previous reports of the low rates of elimination of lipophilic compounds in the desert rodent are therefore not explicable by differences in metabolism. It is suggested that the lower rates of urine production is a more likely explanation. 4. The production of small volumes of concentrated urine is suggested to result in the longer retention of some foreign compounds.

Animals↗
PubMed1975

Characterization of the RNA synthesizing activity of isolated kidney nuclei.

The limiting factor in RNA synthesis by isolated kidney nuclei is RNA nucleotidyltransferase at high salt concentrations but at low salt concentrations template availability becomes limiting. alpha-Amanitin inhibits 85% of the activity at high salt concentrations but only 20-50% of the activity at low salt concentrations. Exogenous DNA is utilized at low salt concentrations [up to 0-1M (NH4)2SO4] but not at high salt concentrations. The effect of increasing salt concentration is mainly to cause an increase in the length of chains synthesized. Initiation rates are not increased by high salt concentrations. The apparent Km for UTP is 8-10 muM at high salt concentrations, indicating that assays performed at low UTP concentrations are likely to give inaccurate results. The activation energy for the reaction at low salt concentration is less than that for the reaction at high salt concentration. The RNA synthesizing capacity of kidney nuclei is dependent on the method of isolation, and preparation by a modification of the Chauveau method (Chauveau et al. 1956) yields the most active nuclei.

Ammonium Sulfate↗