Biomedical subjects
M Hunter
Publications and source records attributed to M Hunter.
Role of cell volume and protein kinase C in regulation of a Cl- conductance in single proximal tubule cells of Rana temporaria.
1. The whole-cell patch clamp technique was used to investigate Cl- currents in single proximal tubule cells isolated from kidneys of Rana temporaria. 2. Immediately following establishment of the whole-cell clamp, the Cl- conductance (gCl) of the cells was low. However, with 2 mM ATP in the pipette there was a time-dependent activation of gCl. Such activation was inhibited when the bath contained a hypertonic Ringer solution. 3. The Cl- conductance was not directly dependent on cell volume; gCl increased with hypotonic shock and decreased with hypertonic shock, but only in the presence of ATP. 4. Activation of gCl by ATP was dependent on extracellular Ca2+; however, the conductance was not directly Ca2+ sensitive. Activation was inhibited by Gd3+, which also had a direct inhibitory action on gCl. 5. Inhibition of protein kinase C (PKC), by 10 microM PKC pseudo-substrate (PKC-ps), completely abolished the ATP-dependent activation of gCl, while stimulation of PKC, by the PKC activator 4 beta-phorbol 12-myristate, 13-acetate (PMA), increased the degree of activation typically observed with ATP. 6. We propose that gCl is activated by PKC-mediated phosphorylation and plays a role in volume regulation of the cells.
Na(+)-H+ exchange in frog early distal tubule: effect of aldosterone on the set-point.
1. Intracellular pH (pHi) regulation was investigated in frog early distal tubule. Single tubules were dissected and perfused, such that the compositions of apical and basolateral solutions could be varied independently. pHi was measured using the fluorescent probe 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF). 2. Brief exposure to NH4+ on the basolateral aspect of the tubules elicited an intracellular acidification, followed by an active recovery. The recovery was inhibited by amiloride and its analogue 5-(N-ethyl-N-isopropyl) amiloride (EIPA) when added to the basolateral, but not the apical, solution. Omission of Na+ from the basolateral solution alone completely inhibited pHi recovery. Thus the Na(+)-H+ exchangers appear to be located on the basolateral membrane. 3. Neither amiloride nor EIPA had any effect on pHi under control conditions, suggesting that the activity of the Na(+)-H+ exchangers at the resting pHi is low. However, removal of basolateral Na+ caused an acidification that was blocked by amiloride, indicating that the Na(+)-H+ exchangers can be activated from the resting state. 4. Intrinsic buffering power (beta i) was determined by stepwise removal of ammonium from the cells in Na(+)-free conditions, to prevent pH regulation, and in the presence of Ba2+ and furosemide (frusemide), to inhibit ammonium transport. beta i was a function of pHi, increasing as pHi decreased. 5. Proton efflux was calculated during the recovery from an acid load in tubules from normal and K(+)-loaded frogs and in tubules which had been incubated for 30 min with aldosterone. Potassium loading produces a chronic increase in plasma aldosterone. Both acute and chronic aldosterone treatment caused an intracellular alkalinization. This was due to an alkaline shift in the set-point of the basolateral Na(+)-H+ exchanger, with no change in the density and/or turnover rate.
Significant improvement to the catalytic properties of aspartate aminotransferase: role of hydrophobic and charged residues in the substrate binding pocket.
The substrate specificity of tyrosine aminotransferase (eTAT) from Escherichia coli has been tested by transferring the critically different residues Leu39, Glu141, and Arg293 into equivalent positions of aspartate aminotransferase (eAAT). These residues are not directly involved in the catalytic process. The single mutant eAAT V39L possesses greater values of kcat/KM not only for tyrosine but also for aspartate and glutamate. In contrast, the double mutant eAAT P141E,A293R and also the triple mutant eAAT V39L,P141E,A293R exhibit smaller changes of kcat/KM. The converse mutants of tyrosine aminotransferase, in which critical residues of eAAT (Val39) and of mitochondrial AAT (Ala39, Val37) were transferred into equivalent positions of eTAT, exhibited generally decreased values of kcat/KM for both dicarboxylic and aromatic substrates. On the basis of the known structures of eAAT and eAAT V39L as well as of a refined model of eTAT, these results indicate that the different substrate specificities of eAAT and eTAT are due to multiple side chain differences and minor rearrangements of the backbone. The generally improved catalytic efficiency of the mutant eAAT V39L appears to be due to an indirect effect, namely, the facilitated closure of the active site upon substrate binding.
Volume regulatory responses in frog isolated proximal cells.
Cells respond to increase in volume by activating solute efflux pathways, resulting in water loss and restoration of the original cell volume. The solute efflux pathways underlying these volume regulatory decrease (VRD) responses have been relatively well studied. However, the transduction pathways whereby the change in cell volume is converted into an intracellular signal resulting in VRD are much less well understood. We have examined VRD in isolated proximal tubule cells from the frog, with particular attention to the roles of stretch-activated channels, Ca2+ and protein kinases. Cell length was taken as an index of cell volume, and was measured continuously using a photodiode array. VRD was observed in approximately 50% of cells, and was inhibited by Ba2+, Gd3+ and 4,4'-diisothiocyanatostilbene 2,2'-disulphonic acid (DIDS), and removal of extracellular Ca2+. VRD was accelerated by the active phorbol ester, phorbol 12-myristate 13-acetate (PMA), and the phosphatase inhibitor F-; on the other hand, VRD was prolonged by 4 alpha-phorbol 12,13-didecanoate (PDC), an inactive phorbol ester), and inhibited by PMA and Gd3+, PMA and 0 Ca2+, and staurosporine. Volume regulation was unaffected by di-butyryl cAMP and 3-isobutyl-1-methyl-xanthene (IBMX). These data suggest that Ca2+ and PKC, via protein phosphorylation, play a stimulatory role in VRD.
Volume-activated, gadolinium-sensitive whole-cell currents in single proximal cells of frog kidney.
Stretch-activated channels (SACs) have been implicated in the control of epithelial cell volume. Such channels are generally sensitive to the trivalent lanthanide, gadolinium (Gd3+). In this study, using Gd3+ sensitivity and volume activation as indices, we have looked for ionic currents attributable to SACs using the whole-cell-patch clamp technique in freshly isolated proximal tubule cells of the frog. Hypotonic shock caused a reversible increase in whole-cell conductance, which was inhibited by Gd3+. In conjunction with this increase in conductance, cell length (measured using an optical technique) also increased. We observed two types of volume- and Gd(3+)-sensitive currents: voltage-dependent IVD and voltage-independent IVI. IVD was found in all cells, activated by depolarisation and hypotonic shock, and was inhibited reversibly by 10 microM Gd3+. The conductance did not discriminate between Na+ and K+ but was slightly anion-selective and was Ca(2+)-permeable. IVI was observed in only 50% of cells and was also inhibited by Gd3+. Although the inhibition was irreversible, it was dose-dependent, suggesting a specific effect of Gd3+ on IVI. Cells that showed IVI had a significantly higher conductance than those that did not (38.7 +/- 4.4, n = 20, and 20.5 +/- 0.7, n = 15, microS.cm-2 respectively). In contrast to IVD, IVI was mildly cation-selective, Ca(2+)-permeable, and also selective for Na+ over K+. As with IVD, volume-induced increases in IVI were inhibited by Gd3+. Both of these currents are activated during hypotonic shock and may be involved in volume-regulatory processes in frog proximal cells.
Callosal morphology and performance on intelligence tests.
Variation in the size of the human corpus callosum was examined in relation to variation in measured IQ. The midsagittal surface area of the corpus callosum, obtained by magnetic resonance imaging, was measured in 47 patients with epilepsy. Intellectual ability was positively related to a larger posterior callosal area. We suggest that the relationship between the posterior callosal region and measured intelligence is "non-functional" in itself, but rather, may reflect other anatomical-cognitive associations. That is, differences in splenial size may reflect differences in the number of cortical neurons and interconnections between areas of the brain that are important for processing the kind of information measured on intelligence tests. Our conclusions, however, must be tempered by a number of factors; in particular, the nature of our subjects and the relatively small sample size.
Detecting dissimulation: profiles of simulated malingerers, traumatic brain-injury patients, and normal controls on a revised version of Hiscock and Hiscock's Forced-Choice Memory Test.
A computer-administered memory test was given to normal subjects instructed to feign brain damage, normal controls, and traumatic brain-injured (TBI) patients with complaints of memory dysfunction. The test, a revised version of an instrument developed by Hiscock and Hiscock (1989) employed forced, two-choice recognition of previously presented five-digit numbers. Two levels of item difficulty and three retention intervals were used. Control and TBI subjects performed at near ceiling level on easy items and items with short retention intervals. Feigning subjects performed worse than TBI and control subjects at all levels of item difficulty and all retention intervals. Subjects groups were maximally distinguishable from one another by performance on difficult items and items with the longest retention interval. All TBI patients performed at or above chance level. Only 15% of the feigning subjects performed below chance level on any section of the test. Jack-knifed discriminant function analysis correctly classified 83% of all subjects into their respective groups. Although evaluation of patient performance relative to chance probability is useful for indicating the presence of extremely exaggerated memory deficits, criteria derived from sample distributions of group scores were superior for evaluation of motivation in less obvious cases. The Victoria Revision may be useful for detecting true memory deficit as well as dissimulation.
A pilot study of the economic cost and clinical outcome of day patient vs inpatient management of active rheumatoid arthritis.
The aims of this pilot study, which compares day patient with inpatient care for management of active RA were (i) to test the feasibility of a trial protocol design including the method of randomization and the practicality of data collection, and (ii) to obtain preliminary information on economic cost and clinical outcome of these two methods of management. Twenty consecutive patients requiring admission for management of active RA were randomized to receive either day patient or inpatient care. All hospital, transport, community and indirect costs incurred over a 6-month period from recruitment were collected for each patient. Disease activity and clinical outcome were assessed using the Ritchie articular index, ESR, Health Assessment Questionnaire, Functional Independence Measure and Hospital Anxiety and Depression Scale. The trial protocol was found to be feasible and no patient allocated to the day patient group requested or required to be transferred to inpatient care. Day care was significantly cheaper than inpatient care despite higher transport costs; the total cost of treating 10 day patients was UK 10,272 pounds compared with 14,528 pounds for 10 inpatients. Clinical outcome was comparable in both groups for all parameters studied and there was no obvious detrimental effect on patients receiving day care. This pilot study demonstrates that day care is feasible and acceptable to patients with active RA. The preliminary data suggest that day care is substantially cheaper than inpatient care and does not apparently compromise clinical outcome.
Validity of Euroqol--a generic health status instrument--in patients with rheumatoid arthritis. Economic and Health Outcomes Research Group.
The main aim of this pilot study was to test the 'construct' validity of Euroqol, a new generic health status instrument which consists of a questionnaire and visual analogue scale. Its ability to measure both current health status and change in health status was assessed in 55 patients with RA. The Euroqol questionnaire and visual analogue scales showed significant and clinically relevant correlations with other condition-specific instruments measuring loss of function, joint pain, joint tenderness and mood; change in these symptoms as measured by the condition-specific instruments was also predictive of change in Euroqol scores. Either component of the Euroqol instrument provide an index of current clinical status and these data provide preliminary evidence for the 'construct' validity of Euroqol in RA. Further work is needed to evaluate more fully the sensitivity of Euroqol to change over time.
Peer and parental influences on adolescents' substance use: a path analysis.
Five hundred and seven 14-to-16-year-old students gave self-report responses to a substance use questionnaire. The questionnaire assessed adolescents' use, preferences, and norms and also their perceptions of their parents' and peers' use and norms in relation to alcohol, tobacco, and tea/coffee. Path analysis revealed that adolescents' internalization of parental and peer pressures is a stronger predictor of substance use than are direct effects. Internalized effects occur by means of preferences rather than norms, and peer pressure is predominantly through modeling behavior, whereas parental influence is through perceived normative standards. Peers' influence is stronger in relation to tobacco use, parental influence is stronger in relation to tea/coffee use, and both are equally important in relation to alcohol use. These findings are discussed in relation to preventive strategies.
Personality and sociodemographic influences on adolescents' substance use: a path analysis.
Five hundred and seven students 14- to 16-years-old gave self-report responses to a substance use questionnaire, the Norwicki-Strickland Locus of Control Scale, and The Piers-Harris Children's Self-Concept Scale. Path analysis revealed that the influence of peers' and parents' use and norms on adolescents' alcohol and tobacco use is mediated by personality, age, sex, and social status effects. Adolescents with external locus of control or low self-esteem "behavior" were more influenced by their peers to smoke. Younger students and girls were more influenced by parental norms than were older students and boys, but only for alcohol and not for tobacco use. Other findings were that girls were not as strongly influenced by their own norms and that girls and low social status adolescents were more influenced by their friend's smoking and drinking. The peers' findings are discussed in relation to substance prevention strategies.
Assessing believable deficits on measures of attention and information processing capacity.
The vulnerability of tests of sustained attention and speed of processing to faked deficits was evaluated by comparing the performances of normal controls, healthy subjects asked to simulate deficits, and patients with closed head injury on a simple auditory reaction-time task and on the PASAT. The results revealed that persons attempting to feign the effects of brain injury perform more poorly than non-malingerers on a simple reaction-time task and the PASAT. The reaction-time task, however, proved more effective than the PASAT at detecting dissimulation, accurately classifying about 76% of the subjects. This value reflects a respectable hit rate for three-group classification.
Impact of menopausal symptoms. Effect on quality of life exaggerated.
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Static and dynamic models of interdisease competition: past and projected mortality from amyotrophic lateral sclerosis and multiple sclerosis.
Longitudinal Gompertzian analysis is an effective method for determining both the pure probability of death for a given condition and the size of inherently susceptible subpopulations [1]. Gompertzian analysis has been used in this study to provide the parameters necessary to construct a stationary population lifetable (static model) of mortality for amyotrophic lateral sclerosis (ALS) and for multiple sclerosis (MS). The static model demonstrates the relative effect of changing general mortality upon the mortality from each specific disease in a situation where interdisease competition is continuously changing. In order to represent mortality in a real population more closely (where age structure is not the result of mortality rates alone) a dynamic model was constructed for both conditions using the age distributions of the population of England and Wales. The quality of the model was verified by comparison of estimated mortality with historical data from the last three decades. The dynamic model has then been used to estimate mortality from each condition over the next three decades on the basis of population projections made by the Central Statistical Office [2], assuming no major change in the factors which lead to either condition. This analysis demonstrates both the theoretical applicability and practical capabilities of Gompertz-derived mortality models for analysing changing mortality patterns.
Wisconsin Card Sorting Performance: effects of age of onset of damage and laterality of dysfunction.
Wisconsin Card Sorting Performance was examined in patients with complex partial seizures of left (n = 35) or right (n = 42) temporal-lobe origin. Our findings suggest that poor performance, in the form of perseveration, occurs in the context of nonfrontal dysfunction and depends not only on the laterality of the epileptogenic disturbance but also on the age of onset of the damage. The ability to shift set is most impaired by left temporal-lobe dysfunction, but only when the damage occurs very early in life. Left temporal-lobe dysfunction after one year of age leaves sorting behavior relatively intact. Perseveration may also occur in the context of right temporal-lobe dysfunction, regardless of the age of onset of the damage, although the deficit tends to be less marked. Finally, the occurrence of the deficit does not depend upon the status of the cerebral speech pattern or general intellectual level.
Rising mortality from motor neurone disease: an explanation.
There is considerable debate about the increasing mortality from motor neurone disease (MND). However, examination of the relationship between increased life expectancy (through decreased general mortality) and increased mortality in both England and Wales and the United States indicates a close association between the two variables. Using a statistical model, defined sub-populations susceptible to MND can be identified in both countries. The size of such a sub-population has been estimated from the 1989 mortality data to be approximately 160,000 people in England and Wales. The proportion of this sub-population dying from MND has increased over the last 30 years, rather than, as previously, dying at an earlier age from other conditions. On this basis, deaths from MND are expected to increase by a further 20% in this sub-population between 1991-2021 because of continuing changes in life expectancy. MND is a condition made increasingly visible in mortality statistics through decreased general mortality, rather than one in which the underlying population at risk has substantially changed. Aetiological extrapolations from the data indicate that susceptibility to the disease is acquired early in life, and that it is unlikely, given the relative stability of the underlying sub-population, that either changed environmental circumstances or artifactual factors can account in themselves for the rise in mortality.
Conductive education and 'alternative' therapies.
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