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Biomedical subjects

M E Anderson

Publications and source records attributed to M E Anderson.

At least 73 records · Page 4Linked to original sources
PubMed1997

The detection of breast microcalcifications with medical ultrasound.

Microcalcifications are small crystals of calcium apatites which form in human tissue through a number of mechanisms. The size, morphology, and distribution of microcalcifications are important indicators in the mammographic screening for and diagnosis of various carcinomas in the breast. Although x-ray mammography is currently the only accepted method for detecting microcalcifications, its efficacy in this regard can be reduced in the presence of dense parenchyma. Current ultrasound scanners do not reliably detect microcalcifications in the size range of clinical interest. The results of theoretical, simulation, and experimental studies focused on the improvement of the ultrasonic visualization of microcalcifications are presented. Methods for estimating the changes in microcalcification detection performance which result from changes in aperture geometry or the presence of an aberrator are presented. An analysis of the relative efficacy of spatial compounding and synthetic receive aperture geometries in the detection of microcalcifications is described. The impact of log compression of the detected image on visualization is discussed. Registered high resolution ultrasound and digital spot mammography images of microcalcifications in excised breast carcinoma tissue and results from the imaging of suspected microcalcifications in vivo are presented.

Breast↗
PubMed1997

Reciprocal interference between the sequence-specific core and nonspecific C-terminal DNA binding domains of p53: implications for regulation.

The tumor suppressor p53 has two DNA binding domains: a central sequence-specific domain and a C-terminal sequence-independent domain. Here, we show that binding of large but not small DNAs by the C terminus of p53 negatively regulates sequence-specific DNA binding by the central domain. Four previously described mechanisms for activation of specific DNA binding operate by blocking negative regulation. Deletion of the C terminus of p53 activates specific DNA binding only in the presence of large DNA. Three activator molecules (a small nucleic acid, a monoclonal antibody against the p53 C terminus, and a C-terminal peptide of p53) stimulate sequence-specific DNA binding only in the presence of both large DNA and p53 with an intact C terminus. Our findings argue that interactions of the C terminus of p53 with genomic DNA in vivo would prevent p53 binding to specific promoters and that cellular mechanisms to block C-terminal DNA binding would be required.

Animals↗
PubMed1997

Pallidal discharge related to the kinematics of reaching movements in two dimensions.

Movement-related discharge of neurons in the internal and external segments of the globus pallidus (GPi and GPe, respectively) of two monkeys was studied during reaching movements in a two-dimensional work-space. Discharge was studied during movements to targets in eight directions and at three distances from the starting position under three behavioral conditions that manipulated target visibility and movement triggering. A total of 73 neurons (57 in GPe and 18 in GPi) with changes in discharge in concert with arm movements were included in a quantitative analysis. Of these, 83% also changed their discharge during manipulation of the contralateral arm outside of the task. Although 73% of changes in discharge began before the initiation of movement, they seldom preceded the initial activity of the antagonist muscles. Decreases in discharge were more common than reported previously, constituting 40% of the changes in discharge detected. In GPi neurons, decreases also tended to begin earlier than increases. Changes in discharge in GPe neurons were of larger magnitude than those in GPi, and increases in discharge were larger than decreases. Onsets of changes in discharge were temporally linked to movement onset in 69% of neurons. Time locking of neural onset to trigger presentation and movement termination was found in only 30 and 1% of neurons, respectively. Direction of movement influenced the magnitude of changes in discharge in 78% of cells. Directional modulations were broadly tuned and preferred directions were uniformly distributed across the range of directions. When directional modulations were large, preferred directions were consistent for different amplitudes of movement and for different behavioral conditions. Amplitude of movement influenced the magnitude of changes in discharge in 78% of cells, and in 80% of cases that relation had a significant linear component. Amplitude effects were not more common or stronger for movements in directions close to a cell's preferred direction. Linear relations to movement amplitude were more common and accounted for more of the trial-to-trial variance in discharge rate than relations to either average velocity or movement duration. The relation to movement amplitude was consistent for two behavioral conditions when the change in discharge was scaled strongly with movement amplitude. Movement-related changes in discharge of neurons in the skeletomotor portions of both pallidal segments reflect the kinematics of movement. This information, encoded in combination with sensory and contextual information, may play an on-line role in the selective facilitation and suppression of different frontal thalamocortical circuits.

Action Potentials↗
PubMed1997

Bcl-6 and lymphoproliferative disorders.

We report a series of 37 cases of lymphoproliferative disorders with 3q27 structural chromosomal abnormalities. Breakpoints at 3q27, the site of the bcl-6 gene, appear in a broad range of B cell lymphoma histologies but are most frequently detected in follicular lymphomas lacking a t(14;18) and diffuse large cell lymphomas. The majority of 3q27 rearrangements result from translocations involving the immunoglobulin heavy or light chain genes, however, involvement of other partner chromosomes is also observed. Molecular rearrangement of bcl-6 is demonstrable in a subset of cases. Bcl-6 is a recently identified gene encoding a zinc-finger protein. It is normally expressed in germinal center B cells where it is believed to have a developmental or differentiation function. Transcriptional deregulation of bcl-6 through translocations, submicroscopic molecular rearrangements or point mutations may be responsible for this gene's putative lymphomagenic potential.

Adolescent↗
PubMed1996

Nodular lymphocyte-predominant Hodgkin's disease associated with large-cell lymphoma: analysis of Ig gene rearrangements by V-J polymerase chain reaction.

The clonality of nodular lymphocyte-predominant Hodgkin's disease (NLPHD) and the relationship to composite or sequential large-cell lymphomas (LCLs) is poorly understood. Clonal Ig heavy-chain gene rearrangements (lgHGR) have infrequently been observed in NLPHD by Southern hybridization. The goals of this study were (1) to determine if IgHGR could be identified by polymerase chain reaction (PCR) techniques in the LCL associated with NLPHD; (2) to determine if the lgHGR identified in the LCL could also be found in the associated NLPHD; and (3) to determine if Epstein-Barr virus (EBV) played a role a role in histologic progression to LCL. Using consensus primers to conserved regions in the lgH variable (V) and joining (J) region genes, we analyzed formalin-fixed paraffin-embedded sections from the biopsies of 25 patients referred to the National Cancer Institute (NCI) registry for NLPHD and LCL using both single-step and seminested V-J PCR. The histologically aggressive component was further subclassified as frank LCL or as L&H-cell-rich, but not fulfilling criteria for LCL. Matched samples representing both NLPHD and aggressive components were available in 13 cases. In 12 cases, only one component was available (aggressive, n = 8; NLPHD, n = 4). In addition, we also amplified, with 32P labeling, 12 cases of NLPHD without associated LCL. Two clonal IgHGR were identified in 29 cases (7%) of typical NLPHD, both of which were associated with LCL containing a similar sized band by PCR. The clonal identity of the bands in the NLPHD and associated LCL was confirmed by sequencing the products in these two cases. Eight of 10 cases (80%) of LCL associated with NLPHD contained a clonal band by this technique. By contrast, none of the cases classified as L&H-cell-rich contained an IgHGR. The single-step and seminested PCR methods produced identical results. All clonal LCLs were studied for EBV sequences by in situ hybridization using the EBER1 probe, and were negative. We conclude that the LCLs associated with NLPHD are clonal B-cell malignancies. However, by these methods, the same clone can be identified in only a minority of cases of NLPHD and LCL. EBV does not appear to play a role in histologic progression. Moreover, our results suggest that many cases suspected of being LCL may actually represent NLPHD with increased numbers of L&H cells. In histologically equivocal cases, the diagnosis of LCL should be reserved for those cases in which a clonal B-cell neoplasm can be demonstrated.

Adult↗
PubMed1996

Spectroscopic states of the CO oxidation/CO2 reduction active site of carbon monoxide dehydrogenase and mechanistic implications.

CO dehydrogenases catalyze the reversible oxidation of CO to CO2, at an active site (called the C-cluster) composed of an Fe4S4 cube with what appears to be a 5-coordinate Fe (called FCII), linked to a Ni (Hu, Z., Spangler, N. J., Anderson, M. E., Xia, J., Ludden, P. W., Lindahl, P. A., & Münck, E. (1996) J. Am. Chem. Soc. 118, 830-845). During catalysis, electrons are transferred from the C-cluster to an [Fe4S4]2+/1+ electron-transfer cluster called the B-cluster. An S = 1/2 form of the C-cluster (called Cred1) converts to another S = 1/2 form (called Cred2) upon reduction with CO, at a rate well within the turnover frequency of the enzyme (Kumar, M., Lu, W.-P., Liu, L., & Ragsdale, S. W. (1993) J. Am. Chem. Soc. 115, 11646-11647). This suggests that the conversion is part of the catalytic mechanism. Dithionite is reported in this paper to effect this conversion as well, but at a much slower rate (kso = 5.3 x 10(-2) M-1 s-1 for dithionite vs 4.4 x 10(6) M-1 s-1 for CO). By contrast, dithionite reduces the oxidized B-cluster much faster, possibly within the turnover frequency of the enzyme. Dithionite apparently effects the Cred1/Cred2 conversion directly, rather than through an intermediate. The conversion rate varies with dithionite concentration. The Cred1/Cred2 conversion occurs at least 10(2) times faster in the presence of CO2 than in its absence. CO2 alters the g values of the gav = 1.82 signal, indicating that CO2 binds to a C-cluster-sensitive site at mild potentials. CN- inhibits CO oxidation by binding to FCII (Hu et al., 1996), and CO, CO2 in the presence of dithionite, or CS2 in dithionite accelerate CN- dissociation from this site (Anderson, M. E., & Lindahl, P. A. (1994) Biochemistry 33, 8702-8711). The effect of CO, CO2, and CS2 on CN- dissociation suggested that these molecules bind at a site (called the modulator) other than that to which CN- binds. The effects of CO2, CS2, CO, and dithionite on the Cred1/Cred2 conversion rate followed a similar pattern, suggesting that this rate is also influenced by modulator binding. Some batches of enzyme cannot convert to the Cred2 form using dithionite, but pretreatment with CO or CO2/dithionite effectively "cures" such batches of this disability. The results presented suggest that the Ni of the C-cluster is the modulator and the substrate binding site for CO/CO2. The inhibitor CS2 in the presence of dithionite also accelerates the decline of Cred1, leading first to an EPR-silent state of the C-cluster, and eventually to a state yielding an EPR signal with gav = 1.66. CS2 binding thus shares some resemblance to CO2 binding. Approximately 90% of the absorbance changes at 420 nm that occur when oxidized CODHCt is reduced by dithionite occur within 2 min at 10 degrees C. This absorbance change occurs in concert with the gav = 1.94 signal development. The remaining 10% of the A420 changes occur over the course of approximately 50 min, apparently coincident with the Cred1/Cred2 conversion. One possibility is that the conversion involves reduction of an (unidentified) Fe-S cluster. A three-state model of catalysis is proposed in which Cred1 binds and oxidizes CO, Cred2 is two electrons more reduced than Cred1 and is the state that binds and reduces CO2, and Cint is a one-electron-reduced state that is proposed to exist because of constraints imposed by the nature of the CO/CO2 reaction and the properties of the clusters involved in catalysis.

Aldehyde Oxidoreductases↗
PubMed1996

Non-invasive assessment of vascular reactivity in forearm skin of patients with primary Raynaud's phenomenon and systemic sclerosis.

We have non-invasively assessed neurovascular control mechanisms in forearm skin of 10 healthy control subjects, eight patients with primary Raynaud's phenomenon (PRP) and 10 patients with systemic sclerosis (SSc) by iontophoresing acetylcholine (endothelial dependent), sodium nitroprusside (endothelial independent) and adrenaline, and measuring subsequent blood flow responses by dual-channel laser Doppler. Because basal forearm blood flow is low, adrenaline response was assessed by attenuation of reperfusion hyperaemia following 60 s of upper arm occlusion. Reperfusion hyperaemia prior to adrenaline iontophoresis differed significantly between groups (F2.21 = 4.3, P = 0.03), being lowest in the SSc and highest in the PRP group. However, the degree of attenuation of this hyperaemia by adrenaline did not differ between groups and all groups demonstrated similar vasodilatory responses to acetylcholine and to sodium nitroprusside. These findings may reflect that abnormalities in vascular tone in patients with Raynaud's phenomenon are local to the digits, or that vasoactive agents not examined in this study play a key role.

Acetylcholine↗
PubMed1996

Differential interaction of temperature-sensitive simian virus 40 T antigens with tumor suppressors pRb and p53.

Previous studies have shown that simian virus 40 large T antigen transforms cells by binding and inactivating suppressors of cell cycle progression and tumor formation. Here, we characterize the interactions of five temperature-sensitive T antigens with the tumor suppressor proteins pRb and p53. All five mutant T antigens bind pRb at the nonpermissive temperature with efficiencies similar to that of wild-type T antigen. A single transformation-competent mutant, with a substitution of amino acid 186, binds p53 at the nonpermissive temperature. Four transformation-defective mutants, with a substitution at T antigen position 357, 422, 427, or 438, are temperature sensitive for the binding and inactivation of p53. Our findings provide a basis for understanding the behavior of cells transformed by temperature-sensitive T antigens.

Animals↗
PubMed1996

Changes in the control of arm position, movement, and thalamic discharge during local inactivation in the globus pallidus of the monkey.

1. To examine the effect of disruption of basal ganglia output on limb stability and movement, muscimol was injected into the internal globus pallidus (GPi) of monkeys trained to make arm movements to visible or remembered targets in a two-dimensional workspace. 2. Injections of as little as 0.25 micrograms muscimol at GPi sites at which pallidal neurons with arm movement activity had been recorded were followed by drift of the contralateral arm within < 10 min. Drift was usually in the flexor direction. Injections at a few sites in or near the external pallidal segment sometimes were followed by extensor drift. 3. Drift was active (accompanied by activation of agonist muscles), but could be overcome by the animal, resulting in an oscillating movement off and on the required position. 4. The pallidal-receiving (PR) area of the thalamus was identified by recording the response of thalamic neurons to stimulation in the globus pallidus. The activity of 15 neurons identified as PR cells (n = 6) or within the PR region was recorded both before and after injection of muscimol into GPi. After the injection, the tonic discharge increased during the hold period in 47% of the cells studied. When postural drift also occurred, there was a close temporal correlation between the postinjection time at which drift occurred and the time at which the tonic discharge rate increased in thalamic neurons that were clearly related to arm movement. 5. The peak velocity of arm movements to visible or remembered visual target locations was decreased after injection of muscimol into GPi, sometimes with an increase in movement time. 6. The firing rate of PR thalamic neurons after injection of muscimol was also increased during the perimovement period. Because of the increase in the tonic discharge rate, however, the phasic movement-related change in activity could stay the same or even decrease. Postinjection changes in this movement-related phasic activity, however, were not necessarily coincident with changes in peak movement velocity. 7. Changes in reaction time were variable after injection of muscimol. In some cases it was increased, and in others decreased. The time of onset of phasic movement-related changes in the activity of PR neurons studied was not altered by the injection. 8. Our data indicate that the tonic inhibitory output of GPi, in particular to the cortical motor areas, is especially important in the maintenance of postural stability. In the absence of normal pallidal output, desired limb position can be achieved on the basis of either current or prior visual cues, but targeted movements are slowed.

Animals↗
PubMed1996

Contrasting locations of pallidal-receiving neurons and microexcitable zones in primate thalamus.

1. In two awake, juvenile male Macaca fascicularis monkeys, microstimulation was applied in ventralis anterior (VA), ventralis lateralis (VL), or ventralis posterior lateralis (VPL) of the thalamus. Thalamic recording was used to identify the region that contained pallidal-receiving (PR) thalamic neurons, cells that responded orthodromically to stimulation in the internal pallidal segment (GPi). Thalamic stimulation was used to elicit motor responses. Penetrations in the thalamus and the pallidum focused on areas with activity related to contralateral arm movement. Fifty-one PR cells were identified electrophysiologically in VL oralis (VLo), VL caudalis (VLc) and VA pars parvocellularis (VApc). 2. With a subject at rest, trains of stimuli were applied through the thalamic microelectrode. Palpable or visible muscle twitches or joint movements were evoked by short trains (12 pulses) of stimuli applied in VLc and VPL oralis (VPLo); thresholds there ranged from 5 to 75 microA. In VA and VLo, areas where PR neurons were located, even longer trains (24 pulses) of stimuli with currents up to 200 microA usually failed to evoke movement. In the caudal portions of VLo, near VPLo, there were some microexcitable sites found near PR cells where stimuli at approximately 50 microA elicited movement. 3. From microstimulation studies combined with histological reconstruction, Ashe and co-workers hypothesized that microexcitable zones were cerebellar receiving areas (CR) and nonexcitable zones were PR areas. Our data support theirs and add electrophysiological identification of PR areas. Further, we injected wheat germ agglutinin-horseradish peroxidase (WGA-HRP) into the thalamus at one of the more rostral microexcitable sites, just caudal and lateral to identified PR cells. The tetra-methyl benzidine-reacted HRP label was found in the contralateral deep cerebellar nuclei (DCN) but not in ipsilateral GPi, showing that even this rostral microexcitable zone was a CR area. 4. Together with evidence from the literature, the data are consistent with the hypothesis that PR cells have relatively weak access to spinal-destined motor outputs, whereas thalamocortical neurons from VPLo and VLc have more secure access. In addition to characteristics of cell discharge and responses to somatosensory stimulation, microexcitability may be a further aid in tentative electro-physiological identification of PR versus CR areas of the motor thalamus without necessarily recording thalamic neuronal responses to stimulation in GPi or the DCN.

Animals↗
PubMed1995

The C-terminal domain of p53 recognizes DNA damaged by ionizing radiation.

p53 accumulates after DNA damage and arrests cellular growth. These findings suggest a possible role for p53 in the cellular response to DNA damage. We have previously shown that the C terminus of p53 binds DNA nonspecifically and assembles stable tetramers. In this study, we have utilized purified segments of human and murine p53s to determine which p53 domains may participate in a DNA damage response pathway. We find that the C-terminal 75 amino acids of human or murine p53 are necessary and sufficient for the DNA annealing and strand-transfer activities of p53. In addition, both full-length wild-type p53 and the C-terminal 75 amino acids display an increased binding affinity for DNA damaged by restriction digestion, DNase I treatment, or ionizing radiation. In contrast, the central site-specific DNA-binding domain together with the tetramerization domain does not have these activities. We propose that interactions of the C terminus of p53 with damaged DNA may play a role in the activation of p53 in response to DNA damage.

Animals↗
PubMed1995

Involvement of Ser-451 and Ser-452 in the catalysis of human gamma-glutamyl transpeptidase.

The serine residue required for catalysis of gamma-glutamyl transpeptidase was identified by site-specific mutagenesis of the conserved serine residues on the basis of sequence alignment of the light subunit of human, rat, pig and two bacterial enzymes. Recombinant human gamma-glutamyl transpeptidases with replacements of these serine residues by Ala were expressed using a baculovirus-insect cell system. Substitutions of Ala at Ser-385, -413 or -425 yielded almost fully active enzymes. However, substitutions of Ala at Ser-451 or -452 yielded enzymes that were only about 1% as active as the wild-type enzyme. Further, their double mutant is only 0.002% as active as the wild type. Kinetic analysis of transpeptidation using glycylglycine as acceptor indicates that the Vmax values of Ser-451 and -452 mutants are substantially decreased (to about 3% of the wild type); however, their Km values for L-gamma-glutamyl-p-nitroanilide as donor were only increased about 5 fold compared to that of the wild type. The double mutation of Ser-451 and -452 further decreased the Vmax value to only about 0.005% of the wild type, while this mutation produced only a minor effect (2-fold increase) on the Km value for the donor. The kinetic values for the hydrolysis reaction of L-gamma-glutamyl-p-nitroanilide in the mutants followed similar trends to those for transpeptidation. The rates of inactivation of Ser-451, -452 and their double mutant enzymes by acivicin, a potent inhibitor, were less than 1% that of the wild-type enzyme. The Ki value of the double mutant for L-serine as a competitive inhibitor of the gamma-glutamyl group is only 9 fold increased over that of the wild type, whereas the Ki for the serine-borate complex, which acts as an inhibitory transition-state analog, was more than 1,000 times higher than for the wild-type enzyme. These results suggest that both Ser-451 and -452 are located at the position able to interact with the gamma-glutamyl group and participate in catalysis, probably as nucleophiles or through stabilization of the transition state.

Amino Acid Sequence↗
PubMed1995

Amino acid sequence of rat kidney glutathione synthetase.

Glutathione (GSH) synthetase [gamma-L-glutamyl-L-cysteine:glycine ligase (ADP-forming), EC 6.3.2.3], an enzyme present in almost all cells, catalyzes the ATP-dependent synthesis of GSH from gamma-L-glutamyl-L-cysteine and glycine. Highly purified preparations of the enzyme have been obtained from rat kidney and several lower forms. The rat kidney enzyme (M(r), 118,000), which contains approximately 2% carbohydrate, is composed of two apparently identical subunits. The cDNA encoding rat kidney GSH synthetase was isolated from a rat kidney lambda gt11 cDNA library by immunoscreening with an antibody prepared against the isolated enzyme. The cDNA contains 1905 nucleotides and an open reading frame of 1422 nucleotides coding for 474 amino acids. The cDNA has a 3' untranslated region of 439 nucleotides, which includes a poly(A) tail. The deduced amino acid sequence (M(r), 52,344) contains all five of the peptide sequences that were independently determined by Edman degradation. The cDNA was expressed in Escherichia coli. The amino acid sequence of the rat kidney enzyme has no significant similarity to that of the enzyme from E. coli and shows some similarity to those deduced for the yeast and frog enzymes. Knowledge of this amino acid sequence is expected to facilitate elucidation of the sequence of the corresponding human enzyme and to lead to studies on the biochemical mechanisms involved in human GSH synthetase deficiency as well as to development of improved methods for prenatal diagnosis of these inborn diseases.

Amino Acid Sequence↗
PubMed1995

Giant leap for p53, small step for drug design.

We review the findings of Cho et al. on the crystal structure of a p53 tumor suppressor-DNA complex. The core DNA binding domain of p53 folds into a structure termed a beta-sandwich, which organizes two loops and a loop-sheet-helix structure on one surface of p53 to interact with the consensus DNA recognition sequence of p53. These structures help to explain the functions of wild-type p53 and the effects of tumor-associated mutations on p53 DNA binding, transactivation and suppression of cellular proliferation.

Animals↗
PubMed1995

Role of cysteine residues in regulation of p53 function.

Previous studies of p53 have implicated cysteine residues in site-specific DNA binding via zinc coordination and redox regulation (P. Hainaut and J. Milner, Cancer Res. 53:4469-4473, 1993; T. R. Hupp, D. W. Meek, C. A. Midgley, and D. P. Lane, Nucleic Acids Res. 21:3167-3174, 1993). We show here that zinc binding and redox regulation are, at least in part, distinct determinants of the binding of p53 to DNA. Moreover, by substituting serine for each cysteine in murine p53, we have investigated the roles of individual cysteines in the regulation of p53 function. Substitution of serine for cysteine at position 40, 179, 274, 293, or 308 had little or no effect on p53 function. In contrast, replacement of cysteine at position 173, 235, or 239 markedly reduced in vitro DNA binding, completely blocked transcriptional activation, and led to a striking enhancement rather than a suppression of transformation by p53. These three cysteines have been implicated in zinc binding by X-ray diffraction studies (Y. Cho, S. Gorina, P.D. Jeffrey, and N.P. Pavletich, Science 265:346-355, 1994); our studies demonstrate the functional consequences of the inability of the central DNA-binding domain of p53 to studies demonstrate the functional consequences of the inability of the central DNA-binding domain of p53 to bind zinc. Lastly, substitutions for cysteines at position 121, 132, 138, or 272 partially blocked both transactivation and the suppression of transformation by p53. These four cysteines are located in the loop-sheet-helix region of the site-specific DNA-binding domain of p53. Like the cysteines in the zinc-binding region, therefore, these cysteines may cooperate to modulate the structure of the DNA-binding domain. Our findings argue that p53 is subject to more than one level of conformational modulation through oxidation-reduction of cysteines at or near the p53-DNA interface.

Adenovirus E1A Proteins↗
PubMed1995

An NMR study of cellular phosphates and membrane transport in renal proximal tubules.

Technical limitations in the measurement of cellular phosphates have hindered studies of interrelationships between cellular Pi, its transport, and its metabolism in renal proximal tubule (PT) cells. We have developed a noninvasive 31P-nuclear magnetic resonance (NMR) probe-perifusion system to measure cellular Pi and have utilized this system to investigate relationships in canine PT cells between the membrane transport and the cellular content of Pi. With 1.2 mM Pi in the extracellular medium, the cellular Pi content of PT averaged 4.94 +/- 0.55 nmol/mg protein. Inhibition of Pi uptake by removal of extracellular Pi rapidly decreased all cellular phosphate compounds to values that were between 55 and 85% of control. Partial replacement of extracellular Pi (0.4 mM) increased cellular phosphates up to 84-100% of control values. Inhibition of Na(+)-K(+)-adenosinetriphosphatase uptake by the addition of ouabain failed to change either cellular Pi or organic phosphates. Reducing the basolateral membrane potential with the addition of barium chloride increased cellular Pi content by nearly 30%. Maximal contents of cellular Pi and ATP were achieved at 0.4 mM Pi in the presence of an inwardly directed Na+ gradient and at 0.8 mM Pi in its absence. These data indicate that cellular Pi content in canine PT is regulated by Na(+)-dependent and -independent transport mechanisms and by the membrane potential across the basolateral membrane. Lastly, cellular ATP content was found to be directly proportional to the cellular Pi content over a physiological range.

Adenosine Triphosphate↗
PubMed1995

Directional variation of spatial and temporal characteristics of limb movements made by monkeys in a two-dimensional work space.

1. The directional variation of kinematic and electromyographic (EMG) characteristics of two-joint arm movements made to targets in a two-dimensional work space was studied in monkeys trained to make targeted arm movements under different behavioral conditions. 2. In each animal, kinematic measures of movement (movement amplitude, movement time, peak velocity, and trajectory curvature) and endpoint spatial position within the target zone varied as a function of the direction of the target from the starting position. Movements made toward the body into the ipsilateral hemispace generally had the smallest amplitude, lowest peak velocity, and longest movement time. 3. Although the directional variation in peak velocity could partially be accounted for by predicted anisotropies in the inertial load imposed by the arm, deviations from these predictions suggest that movement amplitude is controlled more rigorously by the CNS. Adjustments in movement time may be used to compensate for inertial anisotropies. 4. The spatial characteristics of movements (amplitude, trajectory curvature, or endpoint error) were influenced little by the visibility of the target during movement, the advanced knowledge of target location, or the presence or absence of an external trigger cue. However, temporal characteristics (movement time, peak velocity, and for some animals, reaction time) varied more as sensory cues were changed. 5. The time of initial EMG activity in muscles acting around the shoulder varied systematically as a function of target direction. A cosine model accounted for a large fraction of the variability in initial onset time, as determined in a trial-by-trial analysis. The amplitude of the EMG activity was more narrowly tuned, however. Muscles acting at the elbow showed less activity and more variable directional tuning. 6. We conclude that directional variations in the kinematic characteristics of movement, and thus, the dynamic force requirements of the task, must be taken into consideration as contributors to the apparent directional coding described for neuronal populations in different portions of the CNS.

Animals↗