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Biomedical subjects

A J Baker

Publications and source records attributed to A J Baker.

At least 91 records · Page 5Linked to original sources
PubMed1995

The myosin catalytic domain does not rotate during the working power stroke.

Electron paramagnetic resonance spectroscopy of a spin probe attached to cys-707 on myosin cross-bridges was used to monitor the orientation of the myosin catalytic domain at the beginning and end of the working power stroke in active muscle. Elevated concentrations of orthophosphate and decreased pH were used to shift the population of cross-bridges from force-producing states into low force, pre-power-stroke states. The spectrum of probes in active fibers was not changed by conditions that reduced tension by 70%, indicating that the orientation of the catalytic domain was the same at the beginning and end of the power stroke. Thus the data show that the catalytic domain remains rigidly oriented on the actin filament during the power stroke.

Animals↗
PubMed1995

Determinants of postoperative hypothermia after normothermic cardiopulmonary bypass.

Inadvertent postoperative hypothermia in the cardiac surgical patient can have various adverse physiologic effects. Previous studies have investigated the relationship of patient, surgical, and anesthetic factors with postoperative hypothermia in patients undergoing noncardiac surgery. This study was designed to assess the relationship between postoperative hypothermia after normothermic cardiopulmonary bypass (CPB) for cardiac surgery and a variety of perioperative and patient factors. Fifty-six patients undergoing daytime elective or urgent cardiac surgery with warm (37 degrees C) CPB were studied. The following patient variables were included: age, weight, height, sex, history of previous cardiac surgery, and prebypass temperature. The following treatment factors were recorded: type of surgery, type and dose of anesthetic, use of airway humidifier, use of an intravenous (i.v.) fluid warmer, total volume of i.v. fluid administered during surgery, net fluid volume administered via CPB, total time spent on CPB, use of nitroglycerin, use of alpha-agonists during surgery, and elapsed time from end of CPB to end of surgery. Core temperature readings, as measured by a pulmonary artery catheter thermistor, were noted as follows: (1) on insertion of the pulmonary artery catheter; (2) after the patient was weaned from CPB; (3) within 30 minutes of intensive care unit (ICU) arrival; (4) 3 to 5 hours after ICU arrival; (5) 7 to 9 hours after ICU arrival; and (6) 11 to 13 hours after ICU arrival. Multiple linear regression and logistic regression for categorical variables with backward elimination were employed to determine the impact of all variables on lowest postoperative temperature. The lowest mean temperature occurred during CPB.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1995

Mitochondrial DNA variation and population genetic structure of the northern redbelly dace (Phoxinus eos).

Two sections of the control region and the genes coding for NADH dehydrogenase subunits 5 and 6 (ND-5/6) of mitochondrial DNA (mtDNA) were amplified from Phoxinus eos with the polymerase chain reaction. Both sections of the control region were sequenced directly while the ND-5/6 fragment was sequenced in from each end only. Additionally, the entire ND-5/6 fragment was examined for sequence variation using RFLP analysis. No sequence variation was detected in the control region among 70 individuals sampled from 18 populations across three Ontario regions (Spanish River, Madawaska R. and Cataraqui R.). To examine ND-5/6 variation, a total of 75 individuals were sampled from five populations representing two of the three regions (Madawaska River and Cataraqui R.). Six haplotypes were detected by direct sequencing and four by RFLP analysis. Estimates of population subdivision from RFLP data, sequence analysis, and the two data sets combined for the ND-5/6 fragment, suggest that gene flow is restricted within and between regions. However, estimates of sequence divergence for both sequence and RFLP analysis of this fragment suggested that populations were either founded by already differentiated populations or that populations were founded by a single stock and divergence between regions occurred prior to isolation of populations within regions. These estimates of population structure are much greater than those obtained from allozyme analysis. Additionally, high levels of heterozygosity in nuclear DNA, but low mtDNA diversity suggests that populations have experienced reductions in population size sufficient to reduce only mtDNA variation. Random lineage extinction and limited time for the accumulation of new mutations are likely responsible for low levels of mtDNA variation in ND-5/6 and the control region, while functional constraints may limit variation more than expected in the control region in dace and other fishes.

Animals↗
PubMed1995

Effects of intracellular acidosis on Ca2+ activation, contraction, and relaxation of frog skeletal muscle.

The goal of this study was to determine the effects of intracellular acidosis (pH approximately 6.3) of frog skeletal muscle on force and on intracellular Ca2+ concentration ([Ca2+]i; measured at 20 degrees C using indo 1 fluorescence). Acidosis reduced tetanic force by only 11 +/- 2% (mean +/- SE, n = 8) but increased tetanic [Ca2+]i by 33 +/- 6%, suggesting that acidosis reduced the maximum Ca(2+)-activated force. During relaxation, the [Ca2+]i at half-maximal force was doubled with acidosis, suggesting that acidosis altered the Ca(2+)-force relationship. Acidosis markedly slowed force relaxation and [Ca2+]i decline (time constants fitted to force and [Ca2+]i during relaxation increased by 133 +/- 20 and 68 +/- 13%, respectively, with acidosis), suggesting that slowed force relaxation with acidosis may arise from slowed Ca2+ clearance from the cytosol. Late in relaxation, at approximately 30% of initial force, there was a transient phase of [Ca2+]i increase that was delayed with acidosis in proportion to the slowing of force relaxation. This is consistent with previous suggestions that dissociation of cross-bridges from the thin filament during relaxation promotes Ca2+ release to the cytosol from troponin. This study concludes that in skeletal muscle acidosis has little effect on tetanic force and that the major effects are decreased Ca2+ sensitivity and slower relaxation.

Acidosis↗
PubMed1994

Inhibitory actions of salmeterol on human airway macrophages and blood monocytes.

The effect of beta 2-adrenoceptor agonists, salmeterol and salbutamol on thromboxane B2 release from human airway macrophages and peripheral blood monocytes has been examined. Salbutamol (0.1-100 microM) had no inhibitory effect on the release of thromboxane B2 from human airway macrophages. Salmeterol (0.1-100 microM) caused dose-dependent inhibition of thromboxane B2 release from human airway macrophages stimulated by either zymosan or calcium ionophore A23187. This inhibition was not blocked by propranolol (1 microM). The activity of adenylyl cyclase in homogenates of human airway macrophages was increased by NaF (10 mM) by 8.5-fold and salmeterol (100 microM) and isoprenaline (10 microM) by 1.6- and 1.4-fold, respectively. Isoprenaline alone was inhibited by propranolol (1 microM). Salmeterol caused a biphasic inhibition of peripheral blood monocyte thromboxane B2 release. The inhibition at low (10 nM) concentrations of salmeterol was blocked by propranolol and that at higher concentrations (100 microM) was unaffected. The long lipophilic tail of salmeterol had similar inhibitory effects on the airway macrophages to salmeterol itself, and on the peripheral blood monocytes its action resembled that of the highest concentrations of salmeterol used. It is concluded that salmeterol inhibits mediator release from human airway macrophages by a beta-adrenoceptor independent mechanism and from blood monocytes by both beta-adrenoceptor and non-beta-adrenoceptor mechanisms. The latter mechanism may be associated with the lipophilic properties of the salmeterol molecule.

Adenylyl Cyclases↗
PubMed1994

Metabolic and nonmetabolic components of fatigue monitored with 31P-NMR.

The goal of this study was to determine the roles of metabolic and nonmetabolic factors in muscle fatigue. Rat gastrocnemius muscles were fatigued by stimulation of the nerve (n = 6) or muscle (n = 4, after 2 days of denervation). 31Phosphorus nuclear magnetic resonance spectroscopy was used to measure levels of intracellular inorganic phosphate (Pi) and hydrogen ions (H+) (which are thought to inhibit contraction) and the high-energy phosphates, phosphocreatine (PCr), and ATP. For both indirect and direct stimulation, with fatigue to approximately 60% initial tetanic force, [Pi] increased from approximately 3.5 mmol/L to approximately 20 mmol/L and [PCr] decreased from approximately 27 mmol/L to approximately 9 mmol/L. However, with continued fatigue to 25-35% initial tetanic force, neither [Pi] or [PCr] changed further. [ATP] and pH changed only slightly during fatigue. The results are consistent with early fatigue arising from metabolic inhibition of contraction; but later fatigue arising independent of metabolites, due to impaired activation beyond the neuromuscular junction.

Adenosine Triphosphate↗
PubMed1994

Evolution of mtDNA D-loop sequences and their use in phylogenetic studies of shrews in the subgenus Otisorex (Sorex: Soricidae: Insectivora).

mtDNA D-loop sequences were examined in shrews of the genus Sorex. All specimens possessed an array of tandem repeats in which each repeat was 78 to 80 base pairs (bp) in length. Each specimen also possessed a 76-bp imperfect copy of the tandem repeats. Three observations are consistent with the tandem repeats being the product of concerted evolution: (1) the repeats are capable of forming secondary structures; (2) there was minimal sequence divergence between tandem repeats within individuals; and (3) although the tandem repeats and the imperfect repeat presumably arose due to a duplication event in an ancestor of the shrews, the imperfect repeat per se was not copied in any of the specimens observed. Interspecific homology can therefore be assumed for the imperfect repeat. Furthermore, given the apparent high rate of concerted evolution within a genome, tandem repeats in different individuals may be compared as though only a single copy were present. By including data from the imperfect repeat, the last tandem repeat, and the surrounding unique sequence cladistic and genetic distance approaches to phylogeny reconstruction indicated two sister groups within the subgenus Otisorex. One group was composed of Sorex fumeus and the S. cinereus species complex and the other group was composed of S. hoyi, S. monticolus, S. vagrans, and S. palustris. Resolution of relationships among recently evolved taxa demonstrated the usefulness of selected regions of the D-loop for molecular systematic studies.

Animals↗
PubMed1994

Measurement of body surface area in children with liver disease by a novel three-dimensional body scanning device.

Body surface area (BSA) is used in paediatrics to assess fluid requirement, drug doses, cardiac output and glomerular filtration rate. The aim of this study was to examine, in children with liver disease, the relationship between BSA determined by a traditional nomogram and BSA measured by a novel three-dimensional technique--Loughborough Anthropometric Shadow Scanner (LASS). Subjects were 16 children, mean age 8.1 (range 3.6-14.9) years, with a variety of liver diseases. Twenty-eight controls had a mean age of 7.1 (3.1-10.5) years. All had LASS scans performed as well as 21 anthropometric measurements taken by a single observer. There was a significant relationship between BSA (LASS) and BSA nomogram for liver-diseased children (r = 0.99) and controls (r = 0.96). The BSA nomogram values were significantly greater (P < 0.05) than BSA (LASS) for liver-diseased subjects by 10.1% (-0.35 to +20.6; 95% confidence interval), and for controls by 9.6% (4.1-23.2). Best prediction of BSA (LASS) for liver-disease subjects used height, body weight and gluteal furrow circumference [r2 = 0.997; standard estimated error (SEE) = 0.015 m2] and for controls used body weight alone (r2 = 0.907; SEE = 0.048 m2). BSA nomogram has no additional error in children with liver disease, but may overestimate BSA by 10% compared with a novel three-dimensional body surface scanning technique.

Adolescent↗
PubMed1994

Protein and acidosis alter calcium-binding and fluorescence spectra of the calcium indicator indo-1.

The fluorescent indicator indo-1 is widely used to monitor intracellular calcium concentration. However, quantitation is limited by uncertain effects of the intracellular environment on indicator properties. The goal of this study was to determine the effects of protein and acidosis on the fluorescence spectra and calcium dissociation constant (Kd) of indo-1. With 350 nm excitation light, the ratio of indo-1 fluorescence in the absence versus the presence of saturating Ca2+ at wavelength lambda (S lambda) and Kd increased with [protein]. At pH 7.3, Kd, S400, and S470, which were 210 nM, 0.033, and 1.433 in the absence of protein, increased to 808 nM, 0.161, and 2.641, respectively, by adding proteins from frog muscle and to 638 nM, 0.304, and 3.039, respectively, by adding proteins from rat heart. Effects of protein on indo-1 fluorescence were reduced at higher [indo-1]. Acidosis (pH 6.3) had separate effects, which were additive to those of protein: in the absence of protein, acidosis increased Kd to 640 nM; frog muscle proteins further increased Kd to 1700 nM. Acidosis also changed S lambda slightly. In summary, interaction with protein or protons alters indo-1 calcium-binding and fluorescence. These findings are consistent with several previous studies and suggest that indo-1 calibration constants need to be derived in the presence of appropriate types of protein, ratio of [indo-1]/[protein], and pH.

Acidosis↗
PubMed1994

Mitochondrial control-region sequences in two shorebird species, the turnstone and the dunlin, and their utility in population genetic studies.

We determined the mitochondrial control-region sequences of five turnstones (Arenaria interpres) and three dunlins (Calidris alpina). Comparisons revealed that the central part (part II) is conserved relative to much more variable parts at the beginning (part I) and the end (part III). This pattern of sequence conservation is also found in the control regions of other vertebrates. The average sequence divergence between turnstone and dunlin was 21.8% for part I, 7.5% for part II, and 29.5% for part III. Within-species sequence divergence over the entire control region was much lower, at 0.9% for turnstones and 2.0% for dunlins. In both shorebird species, part III contains a repetitive sequence composed only of A and C nucleotides, which has not been found in the control regions of other birds. A survey of the part I sequences of 25 turnstones and 25 dunlins sampled around the world revealed that these species have very different population genetic structures. Dunlins are not only much more differentiated in their sequences but also have a strongly subdivided population genetic structure. Pleistocene vicariant events combined with strong natal philopatry and high mutation rates of the sequences are likely responsible for this population genetic subdivision. Conversely, part I sequences of turnstones are weakly differentiated and are geographically unstructured. We argue that this is not the result of global gene flow but that, instead turnstones have recently expanded from a refugial population that was bottlenecked.

Animals↗
PubMed1994

Patterns of sequence variation in the mitochondrial D-loop region of shrews.

Direct sequencing of the mitochondrial displacement loop (D-loop) of shrews (genus Sorex) for the region between the tRNA(Pro) and the conserved sequence block-F revealed variable numbers of 79-bp tandem repeats. These repeats were found in all 19 individuals sequenced, representing three subspecies and one closely related species of the masked shrew group (Sorex cinereus cinereus, S. c. miscix, S. c. acadicus, and S. haydeni) and an outgroup, the pygmy shrew (S. hoyi). Each specimen also possessed an adjacent 76-bp imperfect copy of the tandem repeats. One individual was heteroplasmic for length variants consisting of five and seven copies of the 79-bp tandem repeat. The sequence of the repeats is conducive to the formation of secondary structure. A termination-associated sequence is present in each of the repeats and in a unique sequence region 5' to the tandem array as well. Mean genetic distance between the masked shrew taxa and the pygmy shrew was calculated separately for the unique sequence region, one of the tandem repeats, the imperfect repeat, and these three regions combined. The unique sequence region evolved more rapidly than the tandem repeats or the imperfect repeat. The small genetic distance between pairs of tandem repeats within an individual is consistent with a model of concerted evolution. Repeats are apparently duplicated and lost at a high rate, which tends to homogenize the tandem array. The rate of D-loop sequence divergence between the masked and pygmy shrews is estimated to be 15%-20%/Myr, the highest rate observed in D-loops of mammals. Rapid sequence evolution in shrews may be due either to their high metabolic rate and short generation time or to the presence of variable numbers of tandem repeats.

Animals↗
PubMed1994

Energy use by contractile and noncontractile processes in skeletal muscle estimated by 31P-NMR.

The goal of this study was to separately determine ATP use by contractile and noncontractile processes in stimulated skeletal muscle. ATP use by tetanically stimulated bullfrog semitendinosus muscle was monitored at room temperature with in vivo 31P-nuclear magnetic resonance. Oxidative phosphorylation was inhibited by cyanide, and ATP use could therefore be calculated by accounting for ATP derived from the creatine kinase (CK) reaction (measured from decreases in phosphocreatine) and from glycolysis (estimated from decreases of intracellular pH). In unfatigued muscles stimulated at optimal length for force production, total ATP utilization (representing both contractile and noncontractile processes) was 2.5 +/- 0.09 (SE) mM/s (n = 6; 53% ATP from glycolysis, 47% from CK). In separate experiments, cross-bridge interactions between actin and myosin filaments were eliminated by increasing sarcomere length; therefore, with stimulation, residual ATP use reflected only noncontractile processes. In stimulated stretched muscles, ATP utilization was reduced compared with unstretched muscles to 1.07 +/- 0.08 mM/s (61% ATP from glycolysis, 39% from CK). These findings suggest that, during contraction near optimum length, a large proportion (approximately 43%) of ATP is used by noncontractile processes, with more ATP derived from glycolysis than from CK.

Adenosine Triphosphate↗
PubMed1994

Mesangial cell apoptosis: the major mechanism for resolution of glomerular hypercellularity in experimental mesangial proliferative nephritis.

Increases in mesangial cell number may herald glomerular scarring, but they are not irreversible. This study sought mechanisms by which surplus glomerular mesangial cells can be cleared. A small proportion of cultured mesangial cells exhibited typical morphological features of apoptosis (programmed cell death), which was increased by growth factor deprivation or exposure to cycloheximide, stimuli known to increase apoptosis in other cell types. Apoptosis was confirmed by typical internucleosomal chromatin cleavage. In vivo, clear morphological evidence of mesangial apoptosis leading to phagocytosis by neighboring mesangial cells was obtained in self-limited mesangial proliferation induced in rats by Thy1.1 antibody, apoptosis occurring approximately 10-fold more frequently than in the healthy rat glomerulus. Indeed, changes in glomerular cell number in Thy1.1 nephritis strongly suggested that apoptosis is the major cell clearance mechanism counterbalancing cell division, thereby mediating resolution of glomerular hypercellularity in experimental mesangial proliferation.

Animals↗
PubMed1993

Hypervariable-control-region sequences reveal global population structuring in a long-distance migrant shorebird, the Dunlin (Calidris alpina).

Hypervariable segments of the control region of mtDNA as well as part of the cytochrome b gene of Dunlins were amplified with PCR and sequenced directly. The 910 base pairs (bp) obtained for each of 73 individuals complete another of the few sequencing studies that examine the global range of a vertebrate species. A total of 35 types of mtDNA were detected, 33 of which were defined by the hypervariable-control-region segments. Thirty of the latter were specific to populations of different geographic origin in the circumpolar breeding range of the species. The remaining three types indicate dispersal between populations in southern Norway and Siberia, but female-mediated flow of mtDNA apparently is too low to overcome the effects of high mutation rates of the control-region sequences, as well as population subdivision associated with historical range disjunctions. A genealogical tree relating the types grouped them into five populations: Alaska, West Coast of North America, Gulf of Mexico, western Europe, and the Taymyr Peninsula. The Dunlin is thus highly structured geographically, with measures of mutational divergence approaching 1.0 for fixation of alternative types in different populations. High diversity of types within populations as well as moderate long-term effective population sizes argue against severe population bottlenecks in promoting this differentiation. Instead, population fragmentation in Pleistocene refuges is the most plausible mechanism of mtDNA differentiation but at a much earlier time scale than suggested previously with morphometric data.

Animals↗
PubMed1993

Isoprenaline inhibits thromboxane B2 release from U937 cells.

The U937 monocytic cell line and its differentiated macrophage-like form have been well characterized, illustrating many similarities with their analogous in vivo cells. We examined the release of thromboxane B2 (TXB2) from undifferentiated and differentiated cells after stimulation with opsonized zymosan and investigated whether the release of this mediator could be modified by isoprenaline. After stimulation, the U937 cells released TXB2 in a dose-dependent manner, with the release greater from the differentiated cells. The TXB2 released was inhibited by flurbiprofen (> 10(-8) M; P < .01) and isoprenaline (> 10(-6) M; P < .01), and the inhibition was reversed by propranolol (10(-6) M; P < .02). Thus, it is clear that undifferentiated and differentiated U937 cells release TXB2, which can be inhibited by beta 2-adrenoceptor stimulation. These findings illustrate an important functional difference between the in vivo macrophages and differentiated U937 cells because beta 2-adrenoceptor stimulation does not inhibit mediator release from macrophages.

Cell Transformation, Neoplastic↗
PubMed1993

Influence of polymer concentration and molecular weight and of enzymic glycocalyx modification on erythrocyte interaction in dextran solutions.

Erythrocytes adhere to each other when suspended in supra-threshold concentrations of dextran of molecular mass of 40 kD or greater. The plasma membranes are parallel to each other over the entire length of the contact seam at the lower effective polymer concentrations. When cells are pretreated with the proteolytic enzyme pronase or the sialidase neuraminidase the membranes are not parallel but make contact at spatially periodic locations along the membrane surface. Pronase induced reduction of cell electrophoretic mobility rapidly reaches a limiting value. Nevertheless, prolonged pre-exposure to enzyme leads to a continuing reduction in contact separations. This result taken with the observation that, for equal loss of electrophoretic mobility, a shorter contact separation results from pronase rather than neuraminidase pre-treatment implies that a non-electrostatic consequence of pronase pre-treatment dominates membrane interaction in the experimental regimes examined here. The average lateral contact separation for different enzyme regimes lay in the range 3.3 microns to a limiting lower value of about 0.7 micron. There was a good correlation between the logarithm of a contact separation index (the approach of separation distance to its limiting value) against the logarithm of a derived index related to net attractive interaction for a wide range of experimental conditions. Treatments which increased attraction or decreased repulsion (e.g. increased dextrans concentration or enzyme pre-treatment) lead to shorter lateral contact separation. This result is qualitatively consistent with the predicted behaviour for the dominant wavelength arising from interfacial instability of a thin aqueous film between adjacent membranes.

Cell Adhesion↗
PubMed1993

Quantitation of cytosolic [Ca2+] in whole perfused rat hearts using Indo-1 fluorometry.

Fluorometric determination of cytosolic calcium, [Ca2+]c, using Indo-1 in intact tissue, is limited by problems in obtaining calibration parameters for Indo-1 in vivo. Therefore, the goal of this study was to calibrate Indo-1 using in vitro constants, obtained from protein-containing reference solutions designed to produce similar Indo-1 spectral properties to those in vivo. Due to wavelength-dependent tissue light absorbance, the in vitro constants had to be absorbance-corrected using a novel method. The correction factor was calculated from the relationship between the Indo-1 fluorescence intensities at the two detection wavelengths. A mixture of proteins at approximately 28 mg/ml had a similar Indo-1 isosbestic wavelength (430 nm) to that found in vivo (427 nm), and a similar fluorescence ratio maximum with saturating Ca2+ to that found in vivo (after absorbance correction). Using calibration constants from this protein mixture, calculated [Ca2+]c in a Langendorf perfused rat heart was 187 nM during diastole, and 464 nM in systole. This new calibration method circumvented the considerable experimental problems of previous methods which required measurements with the cytosol fully depleted and fully saturated with Ca2+.

Animals↗