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Biomedical subjects

S M Dunn

Publications and source records attributed to S M Dunn.

At least 145 records · Page 8Linked to original sources
PubMed1988

Multiple calcium channels in synaptosomes: voltage dependence of 1,4-dihydropyridine binding and effects on function.

The voltage dependence of binding of the calcium channel antagonist, (+)-[3H]PN200-110, to rat brain synaptosomes and the effects of dihydropyridines on 45Ca2+ uptake have been investigated. Under nondepolarizing conditions (+)-[3H]PN200-110 binds to a single class of sites with a Kd of 0.07 nM and a binding capacity of 182 fmol/mg of protein. When the synaptosomal membrane potential was dissipated either by osmotic lysis of the synaptosomes or by depolarization induced by raising the external K+ concentration, there was a decrease in affinity (approximately 7-fold) with no change in the number of sites. The effects of calcium channel ligands on 45Ca2+ uptake by synaptosomes have been measured as a function of external potassium concentration, i.e., membrane potential. Depolarization led to a rapid influx of 45Ca2+ whose magnitude was voltage-dependent. Verapamil (100 microM) almost completely inhibited calcium uptake at all potassium concentrations studied. In contrast, the effects of dihydropyridines (2 microM) appear to be voltage-sensitive. At relatively low levels of depolarization (10-25 mM K+) nitrendipine and PN200-110 completely inhibited 45Ca2+ influx, whereas the agonist Bay K8644 slightly potentiated the response. At higher K+ concentrations an additional dihydropyridine-insensitive component of calcium uptake was observed. These results provide evidence for the presence of dihydropyridine-sensitive calcium channels in synaptosomes which may be activated under conditions of partial depolarization.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1988

Treatment--education.

The educational model which proposed knowledge improvement as a necessary condition for behaviour change (or increased compliance!) is wrong. It ignores the reality that patients fail to comply for many reasons, the least of which is insufficient information. This is not to say that group programmes, or certain types of individual intervention, are not effective in producing change in variables other than factual knowledge, particularly psychosocial factors. There is increasing evidence that formal education programmes are associated with changes in attitude, which may be more a result of the interaction between participants than a response to educational content, and that it is these attitudinal changes which are the precursors to behavioural change. The initial enthusiasm of the medical community for diabetes education as the solution to the major problem of non-compliance has now been replaced by a healthy skepticism. Diabetes education, by itself, has little to offer the patient whose metabolic control is inadequate. The effectiveness of formal education programmes in patients with compromised metabolic control is limited to the few cases where specific information, or a general understanding of diabetes in a newly-diagnosed patient, is lacking. Information deficit is a specific diagnosis with a specific remedy and in many cases the most efficient treatment may be formal education. For the vast majority of patients, however, the information gained from attending traditional diabetes education programmes has very limited implications for behaviour change.

Attitude↗
PubMed1987

Behaviour therapy in the management of patients with anorexia nervosa. A lenient, flexible approach.

Many different treatment approaches have been advocated for anorexia nervosa, and most clinicians now incorporate some aspects of behaviour modification in refeeding an emaciated patient. Traditional operant programmes have required the patient to spend prolonged periods of time confined to a solitary existence in a bedroom devoid of her normal possessions. The present paper evaluated the rate of weight gain in 68 patients with anorexia nervosa (100 consecutive admissions to a specialised eating disorders unit) using a lenient, flexible approach to refeeding. Despite this more humane approach, similar results were achieved when compared to other more rigid behavioural programmes in that they gained 0.16 kg/day. This finding is discussed in the context of the rigid application of behavioural programmes which can be seen as punitive, undermine the patient's co-operation and destroy any therapeutic relationship which may develop.

Adolescent↗
PubMed1987

Complications of intrahospital transport in critically ill patients.

To determine the frequency of hemodynamic and respiratory complications during movement within the hospital, we conducted a prospective study involving 36 critically ill, ventilator-dependent patients who needed procedures done outside the intensive care unit. During the first 20 transports, patients received ventilation through a manual resuscitation bag. Arterial blood gas measurements showed frequent changes from baseline with alterations in PCO2 (greater than 10 torr) or pH (greater than 0.05) occurring on 14 occasions. In a subsequent study, 16 patients received ventilation during transit with the aid of a portable mechanical ventilator. Although 6 patients showed changes in arterial blood gas values, mean changes in PCO2 and pH were significantly less than in the group that received manual ventilatory support. (p less than 0.01). Hemodynamic complications of hypotension and cardiac arrhythmia showed a significant correlation with disturbances in arterial blood gases (p less than 0.05). Although limited by the lack of a control period, this study shows that the transport of critically ill patients may result in severe hemodynamic complications; it also suggests that these complications might be prevented by more careful monitoring of ventilation.

Adult↗
PubMed1986

Acetylcholine receptor dimers are stabilized by extracellular disulfide bonding.

Torpedo acetylcholine receptor (AcChR) exists predominantly as dimers, formed by two monomers held together by a disulfide bridge(s). The dimers are easily cleaved to monomers by reducing agents. 2-mercaptoethanesulfonic acid is shown to be a membrane-impermeant reducing agent which cleaves receptor dimers when it is present only on the outside of intact membrane vesicles. There is no increase in the extent of cleavage when 2-mercaptoethanesulfonic acid is also loaded inside the vesicles. Therefore the disulfide bond(s) involved in the dimerization of the Torpedo acetylcholine receptor is (are) formed by cysteine residues which are exposed on the extracellular side of the membrane.

Animals↗
PubMed1985

Structural and functional aspects of the nicotinic acetylcholine receptor.

The molecular structure of nicotinic acetylcholine receptors (AcChR) from different peripheral tissues and from different brain areas has been studied. AcChRs from Torpedo and Electrophorus electric organ and from piscine, avian, and mammalian muscle have been shown to be highly conserved proteins composed of four types of homologous subunits (alpha, beta, gamma, and delta) which associate in a stoichiometry alpha 2 beta 1 gamma 1 delta 1 to form a pseudosymmetric pentameric complex molecule. Genealogical analysis suggests that all the subunits of these AcChR derive from a common ancestral gene and that the divergence occurred very early in the evolution of the receptor. This shared ancestry and the very early divergence of the four subunits, as well as their highly conserved structures along the animal evolution, suggests that each of the subunits evolved to perform specific crucial roles in the function of the AcChR complex. In Torpedo the two alpha-subunits present in the AcChR molecule are glycosylated to a different extent. This may be the reason why the binding sites for cholinergic ligands that are located on the alpha-subunits are non-equivalent. The pseudosymmetric pentameric complex has all the properties of a physiological receptor with respect to known parameters leading to postsynaptic depolarization, and therefore contains the molecular structure/structures that constitute a cation selective channel for transport across the membrane. The complex also contains recognition sites for acetylcholine, cholinergic antagonists, polypeptide neurotoxins, small molecule neurotoxins, and local anesthetics. Therefore a multiplicity of receptor-ligand associations are possible. This leads to more complex models of such interactions than previously considered.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1985

Brain and muscle nicotinic acetylcholine receptors are different but homologous proteins.

An alpha-bungarotoxin-binding protein was purified from chick optic lobe and brain by an improved method. Previous and present observations justify its designation as a brain nicotinic acetylcholine receptor (AcChoR). It contains subunits whose apparent molecular weights are somewhat larger than those of subunits of peripheral AcChoRs. The size of the optic lobe AcChoR complex is greater than that of the peripheral receptor when estimated from its sedimentation behavior. Brain AcChoR subunits can be specifically precipitated by a monoclonal antibody directed against chick muscle AcChoR. Amino-terminal amino acid sequence analysis was performed on AcChoR preparations and isolated subunits from the optic lobe and from the rest of the chick brain. The sequences obtained demonstrate that, at least for the lowest molecular weight component, the AcChoRs from different brain areas are identical and they are highly homologous to muscle AcChoR. It is concluded that the brain alpha-bungarotoxin-binding protein is indeed a nicotinic AcChoR and is encoded by a set of genes that is different from, but strongly related to, that for the muscle AcChoR.

Amino Acid Sequence↗
PubMed1985

Psychological and attitudinal profiles in donors for artificial insemination.

Few objective data are available concerning the psychological profiles and attitudes of sperm donors in artificial insemination programs. We studied 30 consecutive new volunteers and 45 established sperm donors using the Cattell 16PF personality profile and an attitudinal survey concerning motives for donation, attitudes toward uses of sperm, desire for knowledge of outcomes, and attitudes toward disclosures of identifying and nonidentifying information between the parties to artificial insemination. Donors differed from the population norms in 7 of 16 first-order and 1 of 4 second-order personality factors, and this difference appeared to reflect their self-selection as donors. The predominant motive for donation was altruism, but secondary motives were also common. Financial motivation was very low in this population with few students. Donors approved of all current and most hypothetical uses of sperm but were not in favor of disclosures of information to other participants in the program. Restriction of disclosures to nonidentifying details was more acceptable. Unmarried donors were more often motivated for nonaltruistic reasons and were more in favor of disclosures. Attitudes of sperm donors were mostly stable over at least 3 years, but an increasing minority with time envisaged circumstances that might lead to their withdrawal from the program.

Attitude↗
PubMed1984

The compliance of diabetic patients: relationship between subjective assessment by physicians and objective measurement of patient performance.

During a survey period of 9 months, diabetic patients attending an outpatient clinic were asked routinely by the nursing staff to produce their home urine/glucose monitoring charts and diet charts. If they could not do so, the importance of bringing these charts was explained and they were instructed to bring their charts at subsequent visits. In addition, the individual responses of 109 consecutive patients were monitored as index cases. The physicians of these 109 patients were asked to grade each patient according to their estimate of the patient's compliance. This subjective rating was correlated with the actual performance of the patients in bringing charts. During the survey the overall number of patients attending the clinic who brought urine/blood charts increased from 31% to 59%. The corresponding figures for diet charts were 6% and 21%. Before intervention, the group rated "high compliance" was more likely than the "low compliance" rated group to bring urine/glucose charts. However, after adjustment for this baseline difference the subsequent performances of the high and low rated groups were comparable. These two groups of patients also performed similarly with respect to diet charts. It is concluded that patients judged subjectively to have poor compliance were able to modify their behaviour similarly to those assessed as having good compliance.

Adult↗
PubMed1983

Separate sites of low and high affinity for agonists on Torpedo californica acetylcholine receptor.

We have studied alkylation of the membrane-bound acetylcholine receptor (AcChR) from Torpedo californica electric organ by the cholinergic agonist bromo-acetylcholine (BrAcCh). Following reduction of the AcChR with dithiothreitol (DTT) under strictly controlled conditions, a single class of binding sites was covalently labeled by BrAcCh. The extent of alkylation was dependent on the concentration of both DTT and BrAcCh and reached a maximum when a number of sites equivalent to the number of alpha-bungarotoxin (alpha-BTx) binding sites were labeled. The reaction with BrAcCh was completely inhibited by saturating concentrations of alpha-BTx. On the contrary, complete alkylation of the AcChR with [3H]BrAcCh consistently inhibited only approximately 50% of alpha-BTx binding. The effects of DTT reduction and subsequent BrAcCh alkylation on the cation-gating properties of the AcChR were investigated in rapid kinetic experiments. DTT reduction resulted in a slight decrease in the maximum cation flux and a small shift in the effective dissociation constant to higher acetylcholine (AcCh) concentration. The flux response was completely inhibited by maximal alkylation of the membrane vesicles by BrAcCh. A low-affinity binding site for AcCh, which is likely to be important in AcChR activation, has been revealed for T. californica AcChR by studying the effects of cholinergic ligands on the fluorescence of a probe, 4-[(iodoacetoxy)ethylmethylamino]-7-nitro-2,1,3-benzoxadiazole (IANBD), covalently bound to the AcChR protein. Maximal labeling by BrAcCh did not affect the binding of AcCh to the low-affinity binding site, as monitored by changes in the fluorescence of this probe. This low-affinity binding site must therefore be distinct from the site labeled by BrAcCh. The results strongly support the notion that the nicotinic AcChR contains multiple binding sites for cholinergic ligands.

Acetylcholine↗
PubMed1982

Effects of reduction and alkylation on ligand binding and cation transport by Torpedo californica acetylcholine receptor.

The effects of sulfhydryl group modification on ligand binding and functional properties of the membrane-bound acetylcholine receptor from Torpedo californica have been investigated. Agonist binding kinetics were monitored by changes in fluorescence of the probe 5-(iodoacetamido)-salicylic acid which was covalently bound to the receptor after reduction of a reactive disulfide bond(s) by low concentrations of dithiothreitol. These labeling procedures did not affect either the equilibrium binding constant for [3H]acetylcholine or the number of high-affinity binding sites measured in centrifugation experiments. Further reduction of these labeled receptor preparations by higher concentrations of dithiothreitol and subsequent alkylation by excess iodoacetamide resulted in a more than 10-fold decrease in the affinity of the receptor for [3H]acetylcholine. This reduction and alkylation did not, however, radically alter the observed kinetics of acetylcholine binding. The fluorescence signal change on binding consisted of at least three phases similar to those observed for the control preparations, and the ligand concentration dependencies of the measured rate constants could be described by the same kinetic mechanism involving sequential binding of two ligand molecules and three conformational changes. Variation in the values of some of the kinetic parameters describing the formation of the monoliganded complex adequately accounted for the measured decrease in affinity for [3H]acetylcholine. Stopped-flow fluorescence experiments showed that extensive reduction and alkylation resulted in an apparent loss of the ability of the acetylcholine receptor to mediate agonist-induced cation flux. These results show that reduction of disulfide bonds by high concentrations of dithiothreitol followed by alkylation with iodoacetamide seriously perturbs receptor function although the receptor can still undergo its characteristic conformational changes on the binding of acetylcholine but with altered concentration dependence accounting for the reduced affinity for agonist.

Acetylcholine↗
PubMed1982

Multiple binding sites for agonists on Torpedo californica acetylcholine receptor.

The equilibrium and kinetic properties of agonist binding to the membrane-bound acetylcholine receptor from Torpedo californica have been measured by the fluorescence changes of a probe, 4-[[(iodoacetoxy)ethyl]methylamino]-7-nitro-2,1,3-benzoxadiazole, which was covalently bound to the receptor protein. Dissociation constants for the binding of several agonists have been measured in fluorescence titration experiments, and these are in good agreement with apparent equilibrium constants obtained from the concentration dependence of the cation flux response measured in quantitative in vitro kinetic experiments. These results provide evidence for the existence of a low-affinity binding site for agonists which is likely to be a functionally important site for channel activation. The kinetics of carbamylcholine and acetylcholine binding to this site have been measured in stopped-flow fluorescence experiments. Kinetic traces were recorded over a wide range of agonist concentrations, and all could be fit by a single exponential process whose rate and amplitude increased hyperbolically with the concentration of ligand. The observed signal change has been ascribed to a conformational transition of the receptor-ligand complex, and this occurs on a millisecond time scale at saturating ligand concentrations which is sufficiently fast to suggest a role for this binding site in the process of channel activation. These results indicate that in the Torpedo AcChR activation and desensitization may be parallel processes which are mediated by agonist association with different receptor binding sites.

Acetylcholine↗
PubMed1982

Functional stability of Torpedo acetylcholine receptor. Effects of protease treatment.

The effect of tryptic degradation on structural and functional properties of the membrane-bound acetylcholine receptor from Torpedo californica has been investigated. Under conditions of proteolysis which resulted in extensive degradation of receptor subunits, the membrane preparations retained their full capability of mediating agonist-induced cation flux as measured in rapid kinetic experiments. Low concentrations on trypsin also cleaved receptor dimers to monomers, and this effect was paralleled by degradation of the Mr 65 000 subunits which are known to contain sulfhydryl group(s) involved in receptor dimerization through an interchain disulfide bond(s). This conversion to monomers occurred at lower trypsin concentrations when the enzyme was added to the outside of the vesicles compared with the effects observed when the enzyme was present inside the vesicles. Similarly Mr 43 000 protein consistently found in preparations of the membrane-bound acetylcholine receptor, which can readily be removed without apparent effect on receptor function, displayed greater susceptibility to proteolysis when trypsin was added to the exterior medium rather than inside the vesicles. The results emphasize the full functionality of the monomeric form of the acetylcholine receptor comprised of four polypeptides.

Animals↗