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M H Davis

Publications and source records attributed to M H Davis.

At least 73 records · Page 4Linked to original sources

The effects of private self-consciousness and perspective taking on satisfaction in close relationships.

We extended the scope of recent studies in which self-awareness and perspective taking have been used as predictors of social competence or adjustment: We analyzed their influence on the satisfaction experienced in monogamous, heterosexual relationships. Members of 131 couples answered questions concerning themselves and their relationships. We predicted that individual differences in private self-consciousness would be positively related to relationship satisfaction because of the greater self-disclosure resulting from that heightened self-attention. Second, we predicted that individual differences in perspective taking would foster relationship satisfaction, independent of any influence of self-disclosure. Both expectations were confirmed. Scores on the private self-consciousness scale were predictive of reported self-disclosure, and self-disclosure was predictive of satisfaction in the relationship. Furthermore, once the influence of self-disclosure was removed, no effect of self-consciousness on satisfaction remained. In contrast, after disclosure was controlled, perspective-taking scores were significantly related to satisfaction and were in fact unrelated to disclosure at all. These findings indicate that two personality characteristics having to do with habitual attention to behavioral tendencies, to emotions, and to motivations significantly enhance the quality of close heterosexual relationships in different ways. Results are discussed in terms of current theory in the related fields.

Adolescent↗

Increased membrane permeability to chloride in Duchenne muscular dystrophy fibroblasts and its relationship to muscle function.

Previous studies have suggested an abnormality in Cl- metabolism in Duchenne muscular dystrophy (DMD) fibroblasts. In order to further characterize this abnormality, we have studied 36Cl- distribution and permeability in 11 DMD and 12 normal fibroblast lines. Under steady-state conditions Cl- efflux in fibroblasts is observed to be biphasic, revealing the presence of two major subcellular compartments. Each compartment contains approximately half of the cellular Cl-. The faster of the two observed efflux components is significantly higher in DMD than in control fibroblasts (P less than 0.001). To determine the results of a similar increase in Cl- permeability on skeletal muscle action potentials, we have simulated the effects of increased Cl- conductance on muscle by using a computer model. Effects on the simulated action potential include lower rates of membrane depolarization, lower overpotential, longer duration, and lower input resistance. These effects are similar to those actually observed in DMD muscle.

Action Potentials↗

Analysis of neurotoxin and mitogen-stimulated sodium transport in human fibroblasts.

Human fibroblasts contain two classes of ouabain-insensitive Na+ channels. One channel is activated by alkaloid neurotoxins in combination with scorpion venom, a response which is similar to that of the voltage-sensitive Na+ ionophore of nerve. The other channel is activated by fetal calf serum, several other mitogenic agents, or low extracellular Ca2+. The nervelike Na+ channel is inhibited by tetrodotoxin but not by amiloride, while the mitogen-stimulated channel is blocked by amiloride but not by tetrodotoxin. The combined effects of neurotoxins and low Ca2+ on Na+ uptake are additive, consistent with the conclusion that these Na+ pathways are different and independent. Studies of Na+ efflux show the presence of two intracellular Na+ compartments. When Na+ flux through the (Na+ + K+)-ATPase pump is inhibited by ouabain, compartment A has a high rate constant of efflux (K1 = 0.30 mn-1) and constitutes 60% of the total cellular Na+. Compartment B, with a markedly smaller efflux constant (k2 = -0.07), contains the remaining 40% of cell Na+. Stimulation of flux through the nervelike channel has a pronounced effect on the rate constants and Na+ content of both compartments (K1 = 0.56, k2 = 0.10), but activation of the mitogenic channel has a pronounced effect only on the rate of efflux from compartment A and on the size of compartment B. A cytoplasmic-nuclear model for the Na+ compartments is presented.

Batrachotoxins↗

Creatine kinase activity in normal and Duchenne muscular dystrophy fibroblasts.

Cultured human skin fibroblasts from 9 patients with Duchenne muscular dystrophy (DMD) and 8 normal age- and sex-matched controls were examined for creatine kinase (CK) activity. Both the normal and the DMD fibroblasts were found to have significant levels of CK activity (approximately 10 x 10(-3) IU per milligram of fibroblast protein). The control cells had slightly higher CK activity than the DMD lines, but this difference was not significant (0.2 less than P less than 0.1). The MM (muscle) isozyme, the BB (brain) isozyme, and the MB (hybrid) isozyme, of CK were found to be present in fibroblasts. The isozymes were separated by electrophoresis and the relative amount of each was determined for both normal and DMD cells. In normal fibroblasts, approximately 48% of the total CK activity was of the MM type, 40% was of the BB type, and 12% was of the MB type with no significant differences apparent between normal and DMD groups. The presence in human fibroblasts of significant levels of CK activity with a characteristic isozyme profile is an important consideration for studies of this "marker" enzyme in the pseudohypertrophic muscle of DMD.

Adolescent↗

Decreased structure-linked latency of lysosomal dipeptidyl aminopeptidase-I activity in Duchenne muscular dystrophy fibroblasts.

Crude lysosomal pellets were prepared from skin fibroblasts grown from patients having Duchenne muscular dystrophy, and from normal controls. Disruption of the lysosomes by nonionic detergents resulted in the expression of latent activity of the enzyme dipeptidyl aminopeptidase-I(DAP-I). Duchenne lysosomes showed less structure-linked latency than those from normal controls, and sedimentation studies demonstrated that the difference was not caused by increased leakage of the enzyme from lysosomes. Permeability properties of the lysosomes for an artificial substrate revealed no difference of the apparent Km. However, in intact lysosomes the apparent K, for Cl- of this chloride-requiring enzyme was found to be lower in DMD lysosomes. The apparent increase in entry for Cl- was closely related with the decreased amount of the DAP-I latency. High concentrations of extra-lysosomal Cl- corrected the abnormality.

Cathepsins↗

Identification of a biochemical difference between male and female human fibroblasts: implications for the expression of Duchenne muscular dystrophy.

The lysosomal enzyme dipeptidyl aminopeptidase-I (DAP-I) was reduced in Duchenne muscular dystrophy (DMD) fibroblasts to 30% of the level found in age- and sex-matched controls (p less than 0.005). Structure-linked latency, defined as the increase in DAP-I activity caused by disruption of the lysosomal membrane, was also reduced in Duchenne fibroblasts to 70% of normal levels (p less than 0.001). Duchenne carriers and age- and sex-matched control fibroblasts had similar DAP-I activities and latency. However, the similarity of normal and carrier female DAP-I activities was not due to elevation of the carrier female activities to levels similar to normal males, but rather to reduction of all female DAP-I activities to 30% of normal male levels (p less than 0.001). This gave them comparable activities to those of the male DMD cells. One explanation for these unexpected results would require a modification of the genetics of DMD to that of a Y-influenced X-linked model.

Cathepsins↗

Structural changes in lysosomes from cultured human fibroblasts in Duchenne's muscular dystrophy.

We have previously reported a decreased activity of the lysosomal enzyme dipeptidyl aminopeptidase-I (DAP-I) in cultured fibroblasts from patients with Duchenne's muscular dystrophy (DMD). Here we report that electron microscope examination of these cells reveals the presence of abundant lamellar bodies, a morphologic abnormalities commonly associated with impaired lysosomal function. Morphometric analysis of these cytoplasmic figures in dystrophic cells shows a sevenfold increase relative to normal controls (P less than 0.01). Analysis of lysosomal density profiles by density gradient centrifugation reveals similar patterns in normal and DMD cells. Treatment of lysosomes wit the nonionic detergent Triton X-100 causes an activation of DAP-I. This activation, attributable to structure-linked latency, is markedly diminished in DMD cells which show an optimal activation of only 180% compared to 255% for control fibroblasts (P less than 0.01). These data suggest an alteration in the properties of the lysosomal membrane in DMD fibroblasts. This suggestion is also supported by studies on the release of DAP-I from lysosomes by osmotic shock which show it to be a membrane-associated enzyme with membrane-binding characteristics intermediate between those of tightly bound beta-glucosidase and those of unbound N-acetylgalactosaminidase. The latency characteristics of these other lysosomal enzymes are not altered in the DMD cells, indicating that the effect is specific for DAP-I.

Cathepsins↗

Baroreceptor reflex in the rat after converting enzyme inhibition or angiotensin receptor blockade.

1. One component of baroreflex responsiveness was quantitated in conscious rats using the heart rate response to a pressor injection of phenylephrine. 2. Endogenous angiotensin and its effectiveness were manipulated by sodium deprivation, converting enzyme inhibition and infusion of an angiotensin analogue. None of these manoeuvres changed the observed reflex responsiveness. 3. We conclude that endogenous angiotensin has no influence on the component of baroreceptor function that is described by the slope of the arterial pressure-heart rate relationship.

Angiotensin-Converting Enzyme Inhibitors↗

The effects of cognitive and behavioral control on post-stress performance.

A study was designed to investigate the effects of behavioral and cognitive control on post-stress performance. Half of the subjects exposed to loud unpredictable noise bursts were given "behavioral" control (a button which would terminate the noise), while the other half had no behavioral control. In addition, subjects were provided with one of three levels of feedback (success, failure, or no feedback) regarding their performance during the noise. It was expected that information about performance would provide subjects with an increased sense of "cognitive" control which would affect their appraisal of stressful events and their later performance. The results indicated that subjected that subjects given feedback performed better on subsequent tasks than those given no feedback. Perceived behavioral control had little effect on performance. The causal attributions made by subjects were used to interpret these effects. These findings were viewed as supportive of Averill's notion than various types of control are related to stress in a complex fashion. The data may also support Abramson, Seligman, and Teasdale's reformulation of learned helplessness theory.

Adult↗

Decreased lysosomal dipeptidyl aminopeptidase I activity in cultured human skin fibroblasts in Duchenne's muscular dystrophy.

Several lysosomal enzymes were assayed in cultured human skin fibroblasts from patients with Duchenne's muscular dystrophy (DMD) and age- and sex-matched control patients (N). The activity of four glycosidases, cathepsin B(1), and total autoproteolysis at pH 4.0 were unchanged between the groups, but dipeptidyl aminopeptidase I (DAP-I, or cathepsin C) in the DMD cells was found to be only 30% as active as in the control cells (P < 0.003). This difference is not the result of a redistribution or loss of enzyme during homogenization because the difference occurs in all homogenate fractions. DAP-I activity existing in N and DMD fibroblasts behaves identically with respect to activation by chloride ion, activation by the sulfhydryl reducing agent dithiothreitol, changes in hydrogen ion concentration (pH), changes in substrate concentration (i.e., apparent K(m) values), and changes in temperature (i.e., apparent activation energies). Mixtures of N and DMD cell sonicates display an additivity in DAP-I activity. These results support the conclusion that the catalytic function of the DAP-I molecule is equivalent between N and DMD fibroblasts, and that the decrease in tissue-specific DAP-I activity probably results from the fact that fewer enzyme molecules are present in the DMD cells. These results are also an indication that these nonmuscle cells are expressing some of the phenotypic aspects of the genetic defect in DMD. Cultured human skin fibroblasts may therefore be a useful cellular model in DMD research.

Cathepsins↗

Precordial auscultatory findings in pneumoperitoneum.

A case is reported of a patient in whom a loud precordial click developed postoperatively. The new sound was attributed to pneumoperitoneum. A series of 17 patients is presented who underwent elective surgical procedures that produce pneumoperitoneum. Postoperative precordial auscultation revealed abnormalities in nine which included sounds mimicking clicks or gallops and changes in intensity of previously normal heart sounds. Thus, pneumoperitoneum can produce abnormal precordial auscultatory findings.

Adolescent↗

A restraining cage for instrumented rats.

A rectangular restraining cage for chronically instrumented rats was constructed of acrylic plastic. The cage allowed connections between implanted instrumentation and external recorders through a slot in the top cover. The cage was easy to load and unload through a removable cover plate, and the sidewall was adjustable to accommodate rats of diverse sizes. The cage was easy to dissemble for cleaning, and it was inexpensive.

Animals↗