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Biomedical subjects

P Dunham

Publications and source records attributed to P Dunham.

At least 19 recordsLinked to original sources
PubMed1991

The nonreciprocating robot: effects on verbal discourse, social play, and social referencing at two years of age.

2-year-old children interacted with a robot in a large playroom while their mother sat quietly in the corner. Identical vocalizations from the robot had very different effects on 3 dimensions of the children's behavior when the vocalizations were embedded in reciprocating and nonreciprocating social structures. The reciprocating robot produced (1) more topic-maintaining verbal dialogue, (2) less physical and more linguistically mediated social play, and (3) gender-specific effects on the children's tendency to visually reference their mother during the play session. The data are discussed with reference to the frequently encountered assumption that reciprocal social structures have an impact on children's behavior when the quantity and other qualitative dimensions of social stimulation are held constant, and with reference to the children's attributions about the robot as a social partner.

Child, Preschool↗
PubMed1990

Effects of mother-infant social interactions on infants' subsequent contingency task performance.

20 3-month-old infants participated in a nonsocial contingency task immediately following a social interaction with their mothers. A measure of the time the dyads spent in a state of vocal turn-taking predicted individual differences in the infants' subsequent performance on the contingency task. These results parallel the social transfer effects we reported earlier in which the turn-taking dimension of social structure was experimentally manipulated to assess its effect on a subsequent nonsocial contingency task.

Affect↗
PubMed1989

Coincidence-anticipation performance of adolescent baseball players and nonplayers.

10 adolescent baseball players and 10 nonplayers made estimates of baseballs' arrival at the front edge of a home plate. Balls were projected 45 ft. by a pitching machine at speeds of 35, 40, 45, and 50 mph. Subjects made estimates with the dominant and nondominant eye closest to the oncoming ball. Analysis indicated that players were no more accurate than nonplayers but did respond significantly earlier and with consistency. Eye dominance had no effect on performance.

Acceleration↗
PubMed1989

Social contingency effects on subsequent perceptual-cognitive tasks in young infants.

3 experiments with 3-month-old infants compared the effects of contingent and noncontingent adult-infant social interactions on subsequent infant-controlled habituation and choice tasks. Infants who experienced a prior noncontingent social interaction tended to adopt response strategies that reduced the density of stimulation during these subsequent nonsocial tasks. The results are discussed in terms of their generality and the types of mechanisms that might mediate these transfer effects from social to nonsocial procedures.

Arousal↗
PubMed1988

Effect of practice procedure on skill acquisition.

49 children in Grade 1 in an isolated community were assessed on their form and skill in making a basket for a one-step basketball lay-up following practice using a pseudoshaping, specific, or schema procedure. Analysis gave a significant form effect but no difference in success of making baskets.

Basketball↗
PubMed1987

On the mechanism of stimulation of the Na/K pump of LK sheep erythrocytes by anti-L antibody.

Studies were undertaken to explore the mechanism of stimulation of the Na/K pump in LK sheep erythrocytes by anti-L antibody. First, the numbers of functioning pump sites were determined by correlating [3H]ouabain binding with levels of inhibition of the pump. Untreated (control) cells had approximately 41 pumps per cell, and anti-L treatment caused an increase in the number of functioning pumps to approximately 85 per cell. Reducing the intracellular K concentration, [K]c, to near zero caused an increase in the number of pumps in control cells, but not in anti-L cells, such that the numbers of pumps per cell were about the same in the two cell types. These results led to the prediction that Kc is a noncompetitive inhibitor of the pump in control cells, and that anti-L stimulates the pump and increases number of functioning pumps by reducing noncompetitive inhibition by Kc. Kinetic studies were undertaken to test this prediction: activation of the pump by increasing [Na]c was measured at three fixed levels of [K]c. In control cells, the apparent maximum velocity of the pump (J'max) was reduced approximately threefold by raising [K]c from 0.2 to 9 mmol/liter cells, demonstrating noncompetitive inhibition by Kc. In anti-L cells, J'max did not vary with [K]c, which shows that, as predicted, anti-L abolishes the noncompetitive inhibition by Kc. The modification of the kinetic properties of the pumps by the antibody is highly specific in that affinities for Nac and Ko as substrates are unaffected. However, the effect of the antibody on noncompetitive inhibition by Kc does not explain the stimulation of the pump fully since there is significant stimulation at near-zero [K]c.

Adenosine Triphosphate↗
PubMed1986

Aggregation of marine sponge cells induced by Ca pulses, Ca ionophores, and phorbol esters proceeds in the absence of external Ca.

Cells of the sponge Microciona prolifera dissociated in Ca,Mg-free sea water reaggregate upon addition of Ca, an observation classically attributed to the requirement for Ca of a species-specific aggregation factor. We now report that, unexpectedly, extracellular Ca is not required during aggregation; brief Ca pulses (1-3 sec) terminated by excess EDTA suffice to prepare the cells for aggregation by Ca ionophores (e.g. A23187). We also show that phorbol myristate acetate (PMA) promotes aggregation of pulse-prepared cells. Since PMA and A23187 act synergistically in Microciona, the "twin signal" hypothesis, signalling by Ca and protein kinase C in parallel, is validated in this primitive animal.

Animals↗
PubMed1986

Synergy between phorbol esters, 1-oleyl-2-acetylglycerol, urushiol, and calcium ionophore in eliciting aggregation of marine sponge cells.

Aggregation of marine sponge cells (Microciona prolifera) resembles stimulus-response coupling of higher organisms in which activation of protein kinase C and movements of intracellular Ca provide twin signals. We now report that activators of protein kinase C (phorbol esters) and ionomycin act synergistically to aggregate sponge cells. Surprisingly--since extracellular Ca is required for integrity of the species-specific aggregation factor--synergistic aggregation proceeded in the complete absence of added extracellular Ca (2.5-20 mM EDTA). The order of activity of phorbol esters and related compounds was that of their effect on protein kinase C (phorbol myristate acetate, phorbol dibutyrate greater than phorbol diacetate much greater than phorbol, 4 alpha-phorbol). 1-Oleyl, 2-acetylglycerol a synthetic activator of protein kinase C, also showed synergy with ionomycin. Phorbol esters and 1-oleyl, 2-acetylglycerol acted in synergy with ionomycin to liberate membrane Ca as detected by decreased fluorescence of chlortetracycline in prelabeled cells. Moreover, urushiol, the toxic principle of poison ivy, but not pentadecanylcatechol, its inert analogue, showed synergy with ionomycin. Synergistic aggregation was inhibited by calmidazolium (10 microM), piroxicam (20-100 microM), and pertussis toxin (20 micrograms/ml). The data not only confirm that marine sponge cell aggregation follows the general sequence of stimulus-response coupling in the cells of higher organisms but also support, in this most ancient of multicellular creatures, the hypothesis that mobilization of intracellular Ca and activation of protein kinase C provide the twin signals for cell activation in the absence of added extracellular Ca.

Animals↗
PubMed1986

The number of chloride-cation cotransport sites on Ehrlich ascites cells measured with [3H]bumetanide.

Simultaneous measurements were made of net Cl influxes and [3H]bumetanide binding to Ehrlich ascites tumor cells in which the chloride-cation cotransport pathway had been activated by hypertonic challenge. There was a good linear correlation between inhibition of Cl influx during regulatory volume increase and numbers of bumetanide molecules bound per cell, consistent with high specificity of bumetanide binding to cotransport sites. The extrapolation to the number of bumetanide binding sites per cell at maximal inhibition of Cl transport thus gives the number of cotransport sites per cell as 2.0 X 10(6). From this, and the fluxes measured (not necessarily maximum fluxes), the turnover number is calculated at 50 Cl ions per site per second. Unstimulated cells in isotonic medium, with negligible bumetanide-inhibitable fluxes, have the same number of bumetanide binding sites as the activated cells undergoing volume regulation.

Animals↗
PubMed1979

Inhibitors of membrane transport reduce lysosomal enzyme secretion from dogfish phagocytes and their killing of sea urchin eggs.

Blood phagocytes of the dogfish Mustelus canis attack oocytes of the sea urchin Arbacia punctulata, first provoking a surrogate fertilization response and then killing the eggs. To test the hypothesis that secretion of lysosomal contents is critical in this model of phagocyte-mediated cell injury, we studied effects of agents that modify lysosomal enzyme secretion. Inhibitors of membrane transport (>0.1 mM) inhibited postphagocytic secretion of lysosomal beta-glucuronidase from dogfish phagocytes: phloretin > ethacrynate > furosemide > 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid >> pyridoxal phosphate > ouabain. The same order of activity was found for inhibition by these agents of killing of Arbacia eggs by phagocytes. Cell activation (fertilization response) and cytotoxicity were quantitated both morphologically and by measurements of enzyme (beta-glucuronidase, catalase) release. The agents neither inhibited fertilization responses of eggs to calcium ionophore A23187 nor impaired their viability. Vital staining demonstrated that ethacrynate prevented phagocytes from degranulating upon contact with zymosan particles. The data not only suggest that agents primarily known for their capacity to inhibit membrane transport systems can inhibit lysosomal enzyme secretion from phagocytes but also support the hypothesis that secretion of lysosomal contents mediates activation and killing of target cells in phagocyte-mediated tissue injury.

Animals↗
PubMed1978

Retention of bilateral performance as a function of practice order.

The purpose of this study was to investigate the effect of practice order and initial performance hand on the bilateral retention of a simple tracking skill for 44 undergraduate volunteers. The apparatus was a Lafayette Model 30014 photoelectric rotary pursuit. The circle template was employed with rotation speed set at 20 rpm. Subjects were given 20-sec. trials and required to reach a criterion of 70% time on target twice in succession with both hands. For original practice, subjects were randomly assigned to one of four practice groups: preferred serial, non-preferred serial, preferred sequence and non-preferred sequence. Subjects' performance was recorded as the number of trials required to achieve criterion for both hands. One month later subjects were retested and scored in the same manner. A 2 X 2 X 2 analysis of variance with repeated measures on the last factor was used to determine the effects of initial hand, order of practice, testing periods, and the appropriate interactions. The results indicated that subjects' performance for the two testing periods differed significantly; retest was superior. Order of practice was significant and the sequential order more efficient during both learning and retest.

Adolescent↗
PubMed1977

Membrane fusion: studies with a calcium-sensitive dye, arsenazo III, in liposomes.

Fusion between vesicles, cells, or organelles may be defined as confluence of two membrane-bound compartments without access of their solutes to external milieu. To study fusion by this criterion, we have trapped the metallochromic calcium-sensitive dye, arsenazo III (AIII), partially calcium-saturated (AIII-Ca) in one population of liposomes (phoshatidylcholine 90:dicetylphosphate 10), and ethylene glycol-bis(beta-aminoethyl ether)-N,N'-tetraacetate (EGTA) in a second. In such mixtures, interaction of EGTA with AIII-Ca was measured by a large color shift from blue leads to red (decreased absorbance at 660 nm). Fusion of liposomes (but also lysis and diffusion across the membranes) was proportional to these decrements. The exogenous "fusogens," lysolecithin and retinol, were added to liposomes for 5-24 hr at 37 degrees; after rechromatography, measurements were made of total dye, fraction of dye converted from AIII-Ca to AIII, and total lipid. After correction for lysis and diffusion, lysolecithin (200 microng/ml) induced 23% fusion (volume of AIII liposomes confluent with EGTA liposomes) and retinol (300 microng/ml) induced 15%. With one molar percent cortisol (a membrane stabilizer) in the liposome membranes, fusion induced by fusogens was reduced 2-fold. Neither multi-nor unilamellar liposomes fused with each other in the absence of exogenous fusogens, despite wide variations in molar lipid ratios. Results suggest that liposome-liposome fusion is a slow process requiring exogenous fusogens, which may depend upon contributions of other membrane constituents to mimic closely the fusion of natural membranes.

Arsenicals↗
PubMed1976

Membrane perturbation: studies employing a calcium-sensitive dye, arsenazo III, in liposomes.

A metallochromic dye, arsenazo III [2,7-bis-(2-arsonophenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid], has been incorporated into the aquenous interspaces of multilamellar liposomes. multilamellar liposomes. Addition of Ca produced no shift in the absorbance spectrum of dye captured by liposomes, whereas disruption of liposomes by Triton X-100, followed by Ca, produced the spectrum chracteristic of the dye-Ca complex: evidence of latency. Addition of excess ethyleneglycol-bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA) reversed the spectal shift. Differences between spectra obtained in this sequence yielded dye efflus. To measure Ca efflux, difference spectra (+/-EGTA) were obtained from cationic liposomes containing Ca after detergent lysis (sensitivity less than 10 mmol/ml). Since liposomes were impermeable either to dye or Ca until perturbed, it was possible to test a variety of membrane-active steroids (diethylstilbesterol, deoxycorticosterone, etiocholanolone) for their capacity to provoke dye efflux from liposomes; preincorporation of cortisol stablized liposomes against dye leak. Immunoglobulin-coated liposomes containing dye were taken up by phagocytes of Mustelus canis, and phagocytic vacuoles stained red-purple after ingestions. Liposomes containing the calcium-sensitive dye constitute a simple, accurate means for determining membrane perturbation and Ca fluxes; their uptake by cells or organelles remains to be exploited further.

Animals↗