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Biomedical subjects

A S Harris

Publications and source records attributed to A S Harris.

12 recordsLinked to original sources
PubMed1992

Amino acids and serotonin in Limax maximum after a tryptophan devoid diet.

1. Animals avoid diets lacking an essential amino acid, such as tryptophan (TRP), the precursor for serotonin (5-HT). 5-HT is important in the control of feeding. 2. To study the effects of TRP deprivation, slugs were fed TRP-devoid (DEV) or control (COR) diets. 3. Food intake was depressed in DEV, as expected, but after 2 weeks, the serontonergic metacerebral giant cell in DEV was still functional. 4. Neither brain 5-HT nor plasma TRP concentration was affected. 5. Compared with food-restricted animals that had reductions in most amino acids, the DEV group sustained a marked plasma amino acid imbalance.

Amino Acids↗
PubMed1990

Intranasal desmopressin (DDAVP) by spray in mild hemophilia A and von Willebrand's disease type I.

Desmopressin acetate (1-desamino-8-D-arginine vasopressin, DDAVP) has mostly been given by the parenteral route for the treatment of mild hemophilia A and von Willebrand's disease type I. In the present study the hemostatic effects of desmopressin acetate administered intranasally by spray in a dose of 300 micrograms and intravenously 0.3-0.4 micrograms/kg were assessed and compared in 8 patients with hemophilia A and 22 patients with von Willebrand's disease type I. A bioequivalent response to intravenous and intranasal desmopressin acetate was found in Factor VIII coagulant activity (VIII:C) in the hemophilia patients. In the von Willebrand patients, an equivalent shortening of the bleeding time was seen after the two modes of administration, even though intravenous injection gave a higher increase in plasma levels of VIII:C and vWF:Ag. In five patients with von Willebrand's disease the duration of the spray effect on VIII:C and vWF:Ag was followed for 24 h. After 12 h the mean level of VIII:C was 1.4, and of vWF:Ag 1.5, times the basal level. The findings suggest that the spray can be recommended for home or prophylactic treatment of patients with mild hemophilia A and von Willebrand's disease.

Administration, Intranasal↗
PubMed1990

Calmodulin and calcium-dependent protease I coordinately regulate the interaction of fodrin with actin.

The calcium-dependent proteolysis of fodrin has been implicated in the regulation of secretion, neutrophil and platelet activation, and long-term potentiation in neurons. In vitro studies indicate that calcium-dependent protease I (calpain I) cleaves fodrin in the middle of the alpha subunit and in the COOH-terminal third of the beta subunit. Cleavage at the beta site requires calmodulin, which binds with high affinity to a single site in the alpha subunit. In vitro binding assays, nondenaturing gel electrophoresis, and velocity sedimentation identify a linkage between calcium-dependent protease I proteolysis of fodrin and the ability of calmodulin to regulate the self-association of fodrin and its interaction with actin. Three functional states appear to exist: (i) intact fodrin, which constitutively forms tetramers and binds F-actin; (ii) alpha-cleaved fodrin, which loses its ability to self-associate and bind F-actin in the presence of calmodulin; and (iii) alpha,beta-cleaved fodrin, a form that is incompetent to establish tetramers or bind actin. Because actin binding and fodrin self-association occur at opposite ends of the molecule, whereas calmodulin binds at its center, these results indicate that long-range interactions exist within fodrin. They also offer an example of how two calcium-dependent regulatory processes may act synergistically to reversibly regulate a linkage between the membrane and the cytoskeleton.

Actins↗
PubMed1986

Mechanisms of cytoskeletal regulation: functional and antigenic diversity in human erythrocyte and brain beta spectrin.

A study of human erythrocyte and brain spectrin with particular emphasis on the beta subunits revealed a structural homology but functional dissimilarity between these two molecules. Six monoclonal antibodies raised to human erythrocyte beta spectrin identify three of the four proteolytically defined domains of erythrocyte beta spectrin. Five of these monoclonal antibodies cross-react with human brain spectrin. None of a previously identified set of alpha erythrocyte spectrin monoclonal antibodies [Yurchenco et al: J Biol Chem 257:9102, 1982] reacted with brain spectrin. A domain map generated by limited tryptic digestion shows that brain spectrin is composed of proteolytically resistant domains analogous to erythrocyte spectrin, but the brain protein is more basic. The binding of brain spectrin to erythrocyte ankyrin, both in solution and on erythrocyte IOVs, yielded an association constant approximately 100 time weaker than for erythrocyte spectrin. The binding of azido-calmodulin under native conditions was specific for the erythrocyte beta subunit but was not calcium dependent. In contrast, azido-calmodulin bound only to the alpha subunit of brain spectrin in a calcium-dependent manner. The similarity of structure but modified functional characteristics of the brain and erythrocyte beta spectrins suggest that these proteins serve different cellular roles.

Amino Acids↗
PubMed1985

Mechanism of cytoskeletal regulation (I): functional differences correlate with antigenic dissimilarity in human brain and erythrocyte spectrin.

Human erythrocyte and brain spectrin (fodrin, calspectin) have been compared quantitatively with respect to the extent and sites of antigenic and functional similarity. Brain spectrin cross-reacts strongly with approx. 1% of the epitopes in erythrocyte spectrin, but weakly with at least 50%. The distribution of shared determinants is not uniform. Brain spectrin is most deficient in epitopes characteristic of the 80 kDa and 52 kDa domains of the alpha-subunit (alpha-I and alpha-III) and of terminal portions of the 28 kDa and 74 kDa domains of the beta-subunit (beta-I and beta-IV). The functions associated with these domains also differ between the two proteins. Brain spectrin does not undergo extensive polymerization and binds calmodulin at a different site. The unique ability of erythrocyte spectrin to oligomerize beyond the tetramer reflects its role in the membrane skeleton. Non-erythroid spectrins probably function as specific linkers between membrane receptors and the filamentous cytoskeleton. In this sense, they may act as regulated transducers of information flow between the membrane and the cytoplasmic matrix.

Brain Chemistry↗
PubMed1975

Role of sympathetic excitation in generating arrhythmias in early and late phases of ectopic responses after coronary arterial occlusion in dog heart.

The three phases of arrhythmias that develop within specific durations of occlusion of a coronary artery of the dog have been reviewed and characterized. The intravenous administration of practolol as described has virtually prevented the occurrence of arrhythmic activity during the first 7-8 hr after occlusion and kept the frequency at a much reduced level as compared with controls through 10 or 11 hr, but not appreciably longer. This means that first and second phase arrhythmias were almost abolished, and development of third phase ventricular tachycardia was significantly retarded, but not prevented. It is concluded that sympathetic stimulation is an important component in the effective excitation of ectopic activity during the first and second phases, but contributed no more than a minor component to the fully developed third phase activity.

Animals↗