PubMed Health⌕ Search

Biomedical subjects

W Knox

Publications and source records attributed to W Knox.

9 recordsLinked to original sources
PubMed1998

On the cellular mechanisms by which the bicarbonate ion mediates the extragenomic action of progesterone on human spermatozoa.

Progesterone exerts an extragenomic action on human spermatozoa, inducing a rapid calcium transient in the acrosomal domain of these cells and enhancing their potential for fertilization. This response is known to exhibit an absolute dependence on the presence of extracellular bicarbonate, although the mechanisms underlying this interaction are not understood. In this study, bicarbonate was found to exert a dose-dependent impact on the ability of progesterone to promote sperm-oocyte fusion in the absence of any collateral effect on sperm motility. The loss of sperm function in bicarbonate-free medium was associated with a failure to produce reactive oxygen species, an impaired capacity to exhibit redox-associated changes in tyrosine phosphorylation, and an apparent incapacity to generate normal calcium transients on exposure to progesterone. These defects were not related to a cAMP deficiency but were associated with a significant fall in intracellular pH. If cytosolic pH was chemically buffered into the normal range, then the spermatozoa regained every element of their response to progesterone. These results emphasize the importance of an alkaline intracellular milieu for the extragenomic action of progesterone on human spermatozoa and stress the fundamental difference between intracellular and extracellular sources of bicarbonate in maintaining the proton balance within such cells.

Acrosome↗
PubMed1998

A novel signal transduction cascade in capacitating human spermatozoa characterised by a redox-regulated, cAMP-mediated induction of tyrosine phosphorylation.

Capacitation is a priming event that renders mammalian spermatozoa responsive to signals originating from the cumulus-oocyte complex. The attainment of a capacitated state is dependent upon an increase in tyrosine phosphorylation and results in the acquisition of responsiveness to physiological agonists such as progesterone and ZP3. In this study we have shown that this capacitation-dependent increase in tyrosine phosphorylation is controlled by a unique redox-regulated, cAMP-mediated, signal transduction cascade. Either stimulation of reactive oxygen species generation or elevation of intracellular cAMP induced increases in phosphotyrosine expression by human spermatozoa and enhanced their responsiveness to progesterone. Ultimate convergence of the redox- and cAMP-regulated pathways was indicated by the ability of the protein kinase A inhibitor, H89, to block both modes of signal transduction. Furthermore, the fact that the redox-regulated pathway could be silenced by catalase, while this enzyme had no effect on the cAMP-mediated response, indicated that oxidant generation must lie upstream from cAMP in the reaction sequence. In keeping with this conclusion, a functional association was demonstrated between the redox status of human spermatozoa and their cAMP content. The continuous production of reactive oxygen species was also shown to be necessary for the protein kinase A-tyrosine phosphorylation axis to remain functional. If the generation of oxidising conditions during capacitation was prevented with 2-mercaptoethanol, 2-deoxyglucose or the flavoprotein inhibitor, diphenylene iodonium, then cAMP could no longer trigger tyrosine phosphorylation. These data support a model for human sperm capacitation as a redox-regulated process, involving a unique sequence of interactive events including reactive oxygen species production, elevation of intracellular cAMP, stimulation of protein kinase A and the induction of tyrosine phosphorylation. This is the first report of such a signal transduction cascade and may have implications for the functional significance of reactive oxygen metabolites in other cell types.

Catalase↗
PubMed1997

Reactive oxygen species generation by human spermatozoa is induced by exogenous NADPH and inhibited by the flavoprotein inhibitors diphenylene iodonium and quinacrine.

Human spermatozoa possess a specialized capacity to generate reactive oxygen species (ROS) that is thought to be of significance in the redox regulation of sperm capacitation (De Lamirande and Gagnon, 1993; Aitken et al., 1995). However, the mechanisms by which ROS are generated by these cells are not understood. In this study we have examined the possible significance of NADPH as a substrate for ROS production by human spermatozoa. Addition of NADPH to viable populations of motile spermatozoa induced a sudden dose-dependent increase in the rate of superoxide generation via mechanisms that could not be disrupted by inhibitors of the mitochondrial electron transport chain (antimycin A, rotenone, carbonyl cyanide m-chlorophenylhydrazone [CCCP], and sodium azide), diaphorase (dicoumarol) xanthine oxidase (allopurinol), or lactic acid dehydrogenase (sodium oxamate). However, NADPH-induced ROS generation could be stimulated by permeabilization and was negatively correlated with sperm function. Both NADH and NADPH were active electron donors in this system, while NAD+ and NADP+ exhibited little activity. Stereo-specificity was evident in the response in that only the beta-isomer of NADPH supported superoxide production. The involvement of a flavoprotein in the electron transfer process was indicated by the high sensitivity of the oxidase to inhibition by diphenylene iodonium and quinacrine. These results indicate that NAD(P)H can serve as an electron donor for superoxide generation by human spermatozoa and present a simple strategy for the production of motile populations of free radical generating cells with which to study the significance of these molecules in the control of normal and pathological sperm function.

Acridines↗
PubMed1991

Social support for exercise: relationship to physical activity in young adults.

BACKGROUND: Physical inactivity is an independent risk factor for cardiovascular disease, yet little is known concerning factors which influence participation in physical activity or exercise. Two studies assessed the relationships between self-reported physical activity and social support for exercise. METHOD: One study involved a biracial sample of middle-class male and female teachers (mean age = 38.5 +/- 8.9 years) and one involved a biracial sample of lower- to middle-class males and females (mean age = 35.8 +/- 5.1 years). RESULTS: In both studies the social support scales had high internal consistencies and a two-component solution identical to the original validation study. In both studies, social support for exercise positively correlated with physical activity, but the relationships were mediated by race, gender, specific types of support (i.e., family, friend), and dimensions of physical activity (i.e., global, work, sports, and leisure). In both studies, regardless of work status and race, women's overall activity, particularly during leisure time, was positively related to family support for exercise. In both studies white women's overall activity levels, especially sports and leisure activities, were positively related to friend support. In both studies, black women's sports activity was positively associated with family support. Among white men in both studies, sports activities and total energy expenditure were positively related to family and friend support. Black men's sports-related activity was positively related to family support among the teachers and to friend support among subjects in the second study. CONCLUSION: Findings are discussed in terms of future research directed toward identification of other familial and sociocultural variables which might influence individuals' involvement in physical activity.

Adult↗
PubMed1985

Prosthetic shape replication using a computer controlled carving technique.

This paper describes a carving machine which is the most recently developed module in the suite of CAD/CAM equipment for high technology manufacture and supply of prostheses. It provides the link between the Computer Aided Socket Design (CASD) system and the Rapidform socket manufacturing process. Using the coordinate data produced by the CASD system this machine, under computer guidance, carves from a large block of suitable material a three dimensional object; the equivalent of the rectified plaster model produced by conventional techniques. This provides the form for the fabrication of a socket and the facility completes an integrated system for fabricating, rapidly and cheaply, high quality lightweight prostheses for patients.

Amputation Stumps↗
PubMed1985

The Rapidform process for automated thermoplastic socket production.

This paper describes the genesis of the Rapidform process and its pioneering place in the new developments leading to complete control of the processes of manufacture of prostheses. The materials and geometric considerations involved in the development of a double deformation process under microprocessor control are described. Stages in the development of the system show the advance from the initial application to modular below-knee prostheses through extensions to special suspension systems (supracondylar and suprapatellar) to Syme's and above-knee sockets. The clinical and laboratory results are summarized along with an account of the current aspects of the project, ie advanced clinical trials, testing and analysis. Setting the scene historically for the other computer based modules in this high technology approach to prosthetics, Rapidform has proven to be swift, accurate and economical in its operation. Also, in common with the rest of the suite of equipment, this socket production facility, despite its flexibility and technical sophistication, requires no special services beyond standard single phase mains electricity supply.

Amputation Stumps↗
PubMed1985

Thermoplastic alignment couplings for prostheses.

In the context of modern engineering practice, this paper describes the exploitation of thermoplastic materials for the provision of lightweight, low cost, corrosion free, alignment devices for lower limb prostheses. After setting out design requirements, four newly developed devices are described and discussed. These are respectively a four jack system, a serrated wedge system, a spherical alignment system and a serrated slider. The level of laboratory fatigue testing and experimental field performance is reported and examples are shown of the application of these systems to tapered column thermoplastic below-knee prostheses.

Biomedical Engineering↗