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Biomedical subjects

M Fryer

Publications and source records attributed to M Fryer.

7 recordsLinked to original sources
PubMed1999

Elevated glutathione biosynthetic capacity in the chloroplasts of transgenic tobacco plants paradoxically causes increased oxidative stress

Glutathione (GSH), a major antioxidant in most aerobic organisms, is perceived to be particularly important in plant chloroplasts because it helps to protect the photosynthetic apparatus from oxidative damage. In transgenic tobacco plants overexpressing a chloroplast-targeted gamma-glutamylcysteine synthetase (gamma-ECS), foliar levels of GSH were raised threefold. Paradoxically, increased GSH biosynthetic capacity in the chloroplast resulted in greatly enhanced oxidative stress, which was manifested as light intensity-dependent chlorosis or necrosis. This phenotype was associated with foliar pools of both GSH and gamma-glutamylcysteine (the immediate precursor to GSH) being in a more oxidized state. Further manipulations of both the content and redox state of the foliar thiol pools were achieved using hybrid transgenic plants with enhanced glutathione synthetase or glutathione reductase activity in addition to elevated levels of gamma-ECS. Given the results of these experiments, we suggest that gamma-ECS-transformed plants suffered continuous oxidative damage caused by a failure of the redox-sensing process in the chloroplast.

Journal Article↗
PubMed1997

Creating a supportive environment for Indo-Canadian women.

For Indo-Canadian women, pregnancy and delivery can be very difficult because of the women's lack of knowledge of Western medical procedures and techniques. Young women who have recently immigrated are particularly likely to experience some trauma, for their lack of information is compounded by a lack of social support. Many of these young women have immigrated to enter into an arranged marriage, where the husband and his family are relative strangers. When the young woman becomes pregnant, she may experience considerable stress because of the adjustments she is required to make-to a new language, culture, husband and in-law family as well as to the physical changes associated with pregnancy. Her situation is also significantly affected by the traditional role of the young wife in Indian culture: As the junior woman in the family, she has the lowest status.

Canada↗
PubMed1988

The kinetics relating calcium and force in skeletal muscle.

The kinetics relating Ca2+ transients and muscle force were examined using data obtained with the photoprotein aequorin in skeletal muscles of the rat, barnacle, and frog. These data were fitted by various models using nonlinear methods for minimizing the least mean square errors. Models in which Ca2+ binding to troponin was rate limiting for force production did not produce good agreement with the observed data, except for a small twitch of the barnacle muscle. Models in which cross-bridge kinetics were rate limiting also did not produce good agreement with the observed data, unless the detachment rate constant was allowed to increase sharply on the falling phase of tension production. Increasing the number of cross-bridge states did not dramatically improve the agreement between predicted and observed force. We conclude that the dynamic relationship between Ca2+ transients and force production in intact muscle fibers under physiological conditions can be approximated by a model in which (a) two Ca2+ ions bind rapidly to each troponin molecule, (b) force production is limited by the rate of formation of tightly bound cross-bridges, and (c) the rate of cross-bridge detachment increases rapidly once tension begins to decline and free Ca2+ levels have fallen to low values after the last stimulus. Such a model can account not only for the pattern of force production during a twitch and tetanus, but also the complex, nonlinear pattern of summation which is observed during an unfused tetanus at intermediate rates of stimulation.

Actins↗
PubMed1985

Electrical and chemical stimulation of cervical sympathetic nerves in the dog does not affect secretion of parathyroid hormone.

beta-Adrenergic agonists stimulate PTH release in vitro. The present studies were designed to test the hypothesis that norepinephrine released from sympathetic nerve terminals in the parathyroid glands might be a physiological regulator of PTH secretion. In 22 dogs, electrical stimulation (20 Hz, 1 msec, 50 V nominal) of the right cervical vagosympathetic trunk had no significant effect on release of PTH into the precava, whether the animals were normocalcemic or hypocalcemic, and whether or not they were pretreated with the alpha-adrenergic antagonist phenoxybenzamine. In 4 other dogs, stimulating release of endogenous nerve terminal norepinephrine by iv injection of tyramine (200 micrograms/kg) also failed to raise precaval plasma immunoreactive PTH concentrations. In all studies, induction of mild hypocalcemia raised immunoreactive PTH levels. From these and other studies, we conclude that beta-adrenergic agonists of neural origin are not important regulators of canine PTH release in vivo.

Adrenergic beta-Agonists↗