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Biomedical subjects

Y Tsuda

Publications and source records attributed to Y Tsuda.

At least 307 records · Page 17Linked to original sources
PubMed1978

Nature of catecholamine-like actions of ATP and other energy rich nucleotides on the bullfrog atrial muscle.

The nature of the inotropic actions of exogeneously applied ATP and related compounds (AMP-PNP, GTP, GMP and guanosine) was studied in comparison with that of adrenaline on the bullfrog atrial muscle under voltage clamped and unclamped conditions with the double-gap method. ATP and GTP (10(-6-) - 10(-3) M) produced an immediate positive inotropic effect similar to that achieved with adrenaline. Dose-response curves of these drugs fitted the theoretical dose-response relations, but the curves of ATP and GTP were not significantly altered by propranolol. Under voltage clamped conditions, ATP, AMP-PNP (non-hydrolyzable analogue of ATP) and GTP augmentated the calcium inward current (ICa), ICa-dependent tension and the delayed outward current (Ix) as adrenaline. On the other hand, GMP and guanosine, which have a purine-ribose base but not a high energy phosphate bond, produced a negative inotropic effect, and depressed the Ix as adenosine. All these nucleotides and nucleosides inhibited the ICa-independent tonic tension. The facts that GTP and AMP-PNP showed the same effect as ATP indicated that neither the energy liberation from the phosphate bond nor the substrate for cyclic AMP formation is involved in their positive inotropic effects. It is proposed that the energy rich nucleotides modulate the adenylate cyclase activity, being mediated by some receptor located at the outer surface of the membrane other than beta-adrenergic receptor.

Adenosine Triphosphate↗
PubMed1978

Stabilizing effects of adenosine on the membrane currents and tension components of the bullfrog atrium.

The effects of exogenously applied adenosine on the membrane potentials, currents and tension components of the bullfrog double sucrose-gap method. Adenosine above 10(-3)M produced a prolongation of action potential accompanied by a slight augmentation of contraction which was followed by a sustained depression. The recovery was slow. Under voltage clamp conditions, adenosine merely produced a negative inotropic effect depressing Ica-dependent and -independent tensions. In the membrane currents, Inaf, Is(Ica), Ix and background current (Ib) were all depressed. In the presence of adrenaline, the increased Is, Ix and contraction were inhibited by adenosine in a lower dose (10(-5) -10 (-3) M), and the inhibition of Is and Ica-dependent tension were more prominent in the presence of than in the absence of adrenaline. Under the effect of ATP, which has a catecholamine-like action, similar selective inhibitions were observed. It was concluded that adenosine has a sustained stabilizing action on the myocardium to survive, especially in the presence of adrenaline, by depressing the augmented Ica and contraction.

Adenosine↗
PubMed1977

Stimulation, by two Escherichia coli supernatant proteins, of the initiation of polypeptide synthesis.

Two protein factors (A and B) have been partially purified from Escherichia coli supernatant which, in combination, are more effective than 0.5 M NH4Cl in stimulating ribosomes for AcPhe-tRNA and fMet-tRNA binding, for the puromycin reaction, and for incorporating acetylphenylalanine from AcPhe-tRNA into polypeptide. The factors appear to differ from the initiation factors, the elongation factor EF-T, and ribosomal proteins. Some uncertainty exists as to whether factor B is different from EF-G. To maximize the effect of the factors in initiator tRNA binding, we preincubated the ribosomes with the factors and carried out the binding assay for a short period at 15 degrees C. Maximal stimulation of binding occurred after about a 2-min preincubation at 37 degrees C. Longer preincubation times were required at 15 degrees C, and only slight stimulation was observed after preincubation at 0 degrees C. The extent of stimulation by the factors was not affected when the NH4Cl concentration was increased from 40 to 500 mM in the preincubation. The presence of both the 30S and 50S ribosomal subunits is required for the enhancement of AcPhe-tRNA binding. Polyphenylalanine synthesis carried out without AcPhe-tRNA is inhibited by the factors. It is suggested that the factors may act by inducing a structural rearrangement of the ribosomes.

Bacterial Proteins↗
PubMed1977

An analysis of the action of ATP and related compounds on membrane current and tension components in bullfrog atrial muscle.

The effect of adenosine compounds (ATP, ADP, AMP and adenosine) on membrane potential, current and contractile tension on the bullfrog atrium were studied under voltage clamped and unclamped conditions. The compounds produced immediate positive and late negative inotropic effects in unclamped conditions. The positive inotropic effect and the potency of drugs appeared less marked in the order of ATP, ADP, AMP, and adenosine. Under voltage clamped conditions, only the energy rich compounds, ATP and ADP, produced an enhancement of calcium inward current (Ica) and Ica-dependent phasic tension, while AMP and adenosine elicited a negative inotropic effect. The delayed outward current was initially depressed but later augmented epecially in case of ATP and ADP where Ica was enhanced. All adenosine compounds, however, inhibited the Ica-independent tonic tension. This effect, appearing nonspecific, was ascribable to the action of common structure of these compounds, purine-riboside moiety.

Adenine Nucleotides↗