Search PubMed⌕ Search

Biomedical subjects

R Yamazaki

Publications and source records attributed to R Yamazaki.

At least 91 records · Page 5Linked to original sources
PubMed1975

Multiple cyclic nucleotide phosphodiesterase activities from rat tissues and occurrence of a calcium-plus-magnesium-ion-dependent phosphodiesterase and its protein activator.

1. Supernatant fluids from rat cerebral cortex, cerebellum, kidney, heart and liver contained more phosphodiesterase activity hydrolysing cyclic GMP than that hydrolysing cyclic AMP when assayed with sub-saturating concentrations of substrate. 2. These activities were resolved into several fractions by Sephadex G-200 gel filtration; no two tissues had similar activity profiles. 3. With every tissue examined, a fraction (fraction II) with a molecular weight of about 150,000 was obtained which hydrolysed cyclic GMP preferentially at sub-saturating substrate concentrations in the presence of micromolar concentration of Ca2+, millimolar concentration of Mg2+ and a protein activator. 4. The activity of fraction II accounted for about 60 percent in liver, more than 80 percent in heart and cerebellum, and almost 100 percent in cerebral cortex of the total activity for cyclic GMP hydrolysis, calculated from the activity profiles. 5. Km values of fraction II samples from kidney, heart and liver for cyclic GMP were 1.3, 1.7 and 5 muM respectively. 6. 3-Isobutyl-1-methylxanthine inhibited hydrolysis of cyclic GMP by fraction II with an I50 value of 3muM for heart and liver and 50 muM for cerebrum. 7. The activator protein, with an estimated molecular weight of about 30,000 was isolated from all the tissues listed in 1.8. The concentrations of activator protein and of the isolated enzyme, fraction II, did not correspond exactly.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1975

Ca-2+/Mg-2+-dependent cyclic nucleotide phosphodiesterase and its activator protein.

(1) Ca-2+/Mg-2+-dependent cyclic nucleotide phosphodiesterase was found in the supernatant fluids of a variety of tissues, including cerebral cortex, cerebellum, kidney, liver, and heart. (2) this enzyme required Ca-2+, Mg-2+, and an activator protein (PAF) for the activity. In the presence of these ingredients the enzyme hydrolyzed cyclic GMP preferentially when incubated with a low concentration (0.4 muM) of substrate. (3) The enzyme devoid of PAF was eluted in fraction II with a molecular weight of approximately 150,000 after Sephadex G-200 gel filtration of the supernatant fluids using medium containing EGTA. PAF thus separated from the enzyme was eluted in a fraction corresponding to a molecular weight of approximately 28,000 by gel filtration. Stimulation of the activity of fraction II by Ca-2+ was completely dependent on the addition of PAF. (4) Formation of an active enzyme-PAF complex with an estimated molecular weight of 200,000 was demonstrated by gel filtration of a mixture of the enzyme and PAF in medium containing Ca-2+. It is likely that the activity of the Ca-2+/Mg-2+ in a concentration range of approximately 1 to 10 muM, as shown in the following equation: [Enzyme] inactive + PAF + Ca-2+ in equilibrium [enzyme - PAF - Ca-2+] active. More than one PAF protein may bind to one molecule of enzyme to form an active complex. Equilibrium of the above equation is probably determined mainly by the intracellular concentration of Ca-2+ in vivo. (5) The enzyme-PAF complex was more labile after heat treatment than the free form of enzyme. (6) PAF was isolated from all tissues listed in (1). The levels of PAF and of fraction II did not correspond exactly.

Animals↗
PubMed1973

Regulation of nucleoside cyclic 3':5'-monophosphate phosphodiesterase activity from rat brain by a modulator and Ca2+.

Gel filtration of the 40,000 rpm supernatant fraction of a homogenate of rat cerebral cortex on a Sepharose 6B column yielded two fractions: fraction II with the "Ca(2+) plus Mg(2+)-dependent" phosphodiesterase activity and fraction III containing its modulator. The activity of fraction II was stimulated by micromolar concentrations of Ca(2+) and the modulator when present together; the modulator stimulated the activity of fraction II only when the Ca(2+) concentration was above a threshold value (about 2 muM with 0.4-1 muM substrate), and the stimulatory effect of Ca(2+) was dependent upon the presence of the modulator. A possibility is discussed that the modulator may reversibly bind to the enzyme, which by itself is inactive, to form an active enzyme-modulator complex and that Ca(2+) stimulates the activity of phosphodiesterase by shifting the equilibrium between these three species towards the formation of the active enzyme-modulator complex. Although fraction II hydrolyzed both cyclic AMP and cyclic GMP, hydrolysis of the latter was more significantly influenced by Ca(2+) and the modulator than that of the former, and the "Ca(2+) plus Mg(2+)-dependent" phosphodiesterase is likely to be a cyclic GMP enzyme. This conclusion is based on the following evidence: (a) Ca(2+) stimulated hydrolysis of cyclic GMP by fraction II more than that of cyclic AMP. (b) In the presence of Ca(2+) and the modulator, fraction II hydrolyzed cyclic GMP about 8 times faster than cyclic AMP when incubated with 0.4 muM substrate. (c) Half-maximal stimulation of hydrolysis of cyclic GMP was attained at a lower concentration of Ca(2+) (4 muM) than that of cAMP (8 muM). (d) Increase in the concentration of Ca(2+) from 0.06 muM to 12 muM in the presence of the modulator caused a decrease in the K(m) value of cyclic GMP hydrolysis by fraction II from 20 muM to 2 muM accompanied by 4-fold increase in the V(max) value. Under similar conditions, there was only a slight decrease in the K(m) value of cylic AMP hydrolysis (90 muM --> 50 muM), although the V(max) value increased 7-fold. The anomalous shape of the kinetic plot of cyclic GMP hydrolysis became linear when the Ca(2+) concentration was increased in the presence of the modulator. The modulator seems to be a protein, but it is heat stable. It is probably identical to the protein activator of phosphodiesterase first described by Cheung.

Animals↗
PubMedDate not supplied

Muscle histopathology in spastic cerebral palsy.

We studied the histopathology of spastic muscles in patients with spastic cerebral palsy using specimens obtained from the gastrocnemius muscles during orthopedic operations. Though there was no disease-specific abnormality, we found changes in fiber type distribution, i.e., type-1 fiber predominance and type-2B fiber deficiency. These changes were not found in the patient with brain infarction at age 1 year 5 months. Variation in fiber size, especially in type-1 fibers, was also detected in older patients and at the more severely affected sides. We speculated that the influence on the spinal motor unit from upper motor cortex might be applicable to the muscle histological findings and the time of the onset of the brain damage might be important.

Adenosine Triphosphatases↗
PubMedDate not supplied

Retinal cell death by light damage.

PURPOSE: To determine the relationship between apoptotic photoreceptor cell death and the duration of light exposure. METHODS: Ten-week-old male albino rats (Wistar strain) were dark-adapted for 2 days and then exposed to intense light for 12 hours, and 1, 2, 3, 7, 14, 21, and 28 days. The presence of apoptosis was confirmed by electron microscopy and the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) method. Differences in the apoptotic processes of the photoreceptor cells in the superior, posterior pole, and inferior portions of the retina were determined. RESULTS: Photoreceptor cells showed TUNEL-positive staining, whereas the cells in the inner nuclear layer, ganglion cell layer and retinal pigment epithelia exhibited weak positive or negative TUNEL staining. By electron microscopy, photoreceptor cells showed typical apoptotic nuclear changes and formation of apoptotic bodies. CONCLUSIONS: The sensitivity to light damage and style of death differed among retinal cells by location and cell type.

Animals↗
PubMedDate not supplied

Effects of alpha-adrenoceptor agonists on cardiac output and blood pressure in spinally anesthetized ganglion-blocked dogs.

The alpha-adrenoceptor agonist ST-1059 (2-amino-1-(2,5-dimethoxyphenyl) ethanol), the alpha 1-adrenoceptor agonist methoxamine, the alpha 2-adrenoceptor agonist clonidine and a nonselective alpha-adrenoceptor agonist norepinephrine, all increase cardiac output and dose-dependently increase arterial blood pressure in spinally anesthetized ganglion-blocked dogs. The increase in cardiac output may be the result of an increased venous return via the contraction of capacitance vessels, and the vasopressor responses are attributed to an increase in total peripheral resistance. The increases in cardiac output and pressor responses induced by ST-1059 and methoxamine were antagonized by the alpha 1-adrenoceptor antagonist prazosin (0.3 mg/kg i.v.), but those induced by clonidine were not inhibited. In contrast, the alpha 2-adrenoceptor antagonist yohimbine (0.3 mg/kg i.v.) had little or no effects on the increase in cardiac output or the pressor responses induced by ST-1059 and methoxamine, but strongly attenuated those of clonidine. Prazosin and yohimbine inhibited the norepinephrine-induced increase in cardiac output and pressor responses. These results suggest that the increases in cardiac output and blood pressure induced by ST-1059 were mediated by postjunctional alpha 1-adrenoceptor stimulation, such as by methoxamine, but that those induced by clonidine were mediated by postjunctional alpha 2-adrenoceptor stimulation in dogs. Not only the postjunctional alpha 1-adrenoceptors but also the postjunctional alpha 2-adrenoceptors may play an important role in the constriction of venous beds, as well as of the arterioles in spinally anesthetized ganglion-blocked dogs.

Adrenergic alpha-Agonists↗