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Biomedical subjects

Y Kira

Publications and source records attributed to Y Kira.

51 records · Page 3Linked to original sources
PubMed1984

Effects of noncarbohydrate substrates on protein synthesis in hearts from fed and fasted rats.

An overnight fast reduced RNA content and resulted in lower rates and efficiency of protein synthesis when rat hearts were perfused in vitro and supplied glucose as oxidizable substrate. Decreased efficiency of synthesis was associated with development of a block in peptide chain initiation in hearts of both fed and fasted rats. Provision of pyruvate increased the rate and efficiency of protein synthesis in fasted but not fed tissue, and partially overcame the initiation block in both groups. A mixture of glucose, pyruvate and insulin increased the efficiency of protein synthesis and decreased ribosomal subunit content to similar values in both groups of hearts. Noncarbohydrate substrates, including pyruvate, lactate, acetoacetate and beta-hydroxybutyrate, supported higher rates of protein synthesis than glucose in hearts of fasted, but not fed rats. However, mixtures of glucose and either pyruvate, acetoacetate or beta-hydroxybutyrate increased the synthetic rate in fed tissue. Provision of noncarbohydrate substrates increased energy availability, as indicated by higher creatine-P/creatine ratios in both groups of hearts, but the synthetic rate increased as a function of creatine-P/creatine ratio only in the fasted tissue. Octanoate and leucine accelerated protein synthesis and increased energy availability in the fed tissue. The mixtures of glucose and noncarbohydrate substrates or octanoate elevated glucose-6-P content. These studies indicate that an overnight fast decreased the capacity for protein synthesis and modified the regulation of synthesis by noncarbohydrate substrates.

3-Hydroxybutyric Acid↗
PubMed1984

Aortic pressure, substrate utilization and protein synthesis.

An increase in aortic pressure from 60 to 120 mmHg in Langendorff perfused hearts increased oxygen consumption, glucose utilization, pyruvate oxidation and protein synthesis. These changes were not prevented by insertion of a ventricular drain that prevented intraventricular pressure development. Arrest of the heart with tetrodotoxin markedly reduced oxygen consumption; under these conditions an elevation of aortic pressure did not increase oxygen consumption. Elevation of aortic pressure in arrested-drained preparations supplied either glucose or pyruvate as oxidizable substrate increased protein synthesis to a comparable extent. Energy availability, as assessed by measurements of the creatine-P/creatine ratio, increased as aortic pressure was raised in hearts provided glucose, but not pyruvate, suggesting that greater energy availability was not the factor linking higher aortic pressure to faster rates of synthesis. These results focus attention on stretch of the ventricular wall, as the mechanical factor responsible for the effects of aortic pressure on several metabolic activities of the heart.

Animals↗
PubMed1984

Aortic perfusion pressure as a determinant of cardiac protein synthesis.

Mechanical parameters and intracellular mediators that may control protein synthesis have been studied in isolated rat hearts subjected to increased aortic pressure or induced to perform cardiac work. Elevation of aortic pressure from 60 to 120 mmHg in Langendorff preparations with glucose, glucose plus insulin, or pyruvate raised the rate of protein synthesis during the 2nd h of perfusion. These effects involved faster rates of both peptide chain initiation and elongation. In working hearts supplied glucose or glucose plus insulin, higher rate of synthesis were observed in both the 1st and 2nd h of perfusion, compared with Langendorff preparations perfused at 60 mmHg. Intracellular levels of glucose 6-phosphate, ATP/ADP ratio, adenylate energy charge, or creatine phosphate/creatine did not correlate with the rate of protein synthesis in beating control hearts. When ventricular pressure development was prevented by ventricular draining and hearts were arrested with tetrodotoxin, protein synthesis still increased as a function of perfusion pressure. Oxygen consumption increased as aortic pressure was raised in beating-drained hearts but was unaffected in arrested-drained hearts. These results indicate that intraventricular pressure development, cardiac contraction, oxygen consumption, glucose 6-phosphate, energy availability, and coronary flow could be dissociated from the stimulatory effect of higher aortic pressures on protein synthesis and suggested that stretch of the ventricular wall, as a consequence of increased aortic pressure, could be the mechanical parameter most closely related to the increase in protein synthesis.

Animals↗
PubMed1984

A study of auditory middle latency responses in relation to electrode combinations and stimulus conditions.

Auditory middle latency responses were recorded from healthy right-handed subjects. Acoustic clicks at a rate of 10/s were presented to the subjects via headphones. Using the electrode combination unilateral mastoid-nose tip, responses characterized by two early negative waves (about 11.5 and 18 ms peak latencies), followed by a late positive one (about 30 ms peak latency), were elicited by binaural stimulation (50-dB SL clicks). The waveform of responses from the unilateral mastoid-nose tip combination was similar to that recorded from a combination of the same side mastoid and a balanced noncephalic reference electrode, although the phase was opposite to that recorded from the Cz-unilateral mastoid combination. Auditory middle latency responses were recorded simultaneously from right mastoid and left mastoid and referenced to the nose tip; interaural differences in amplitude were found in most subjects. The amplitudes of the early components for binaural stimulation were larger than those for monaural stimulation.

Acoustic Stimulation↗
PubMed1983

Aortic perfusion pressure and protein synthesis.

The effect of increased pressure load on cardiac protein synthesis has been studied in Langendorff preparations and working hearts supplied glucose as substrate. During the second hour of perfusion, elevation of perfusion pressure from 60 to 120 mmHg in Langendorff preparations accelerated protein synthesis by approximately 40% while induction of cardiac work and development of a systolic pressure of 145 mmHg increased synthesis by 22%, as compared to a Langendorff preparation perfused at 60 mmHg. In Langendorff preparations, increased perfusion pressure still accelerated protein synthesis when a drain was placed in the ventricle and intraventricular pressure development was prevented or when the heart was arrested with tetrodotoxin and the ventricle drained. These results suggest that the enhancement of protein synthesis with a pressure load may be induced by passive stretch of the cardiac muscle cell secondary to increased perfusion pressure.

Animals↗
PubMed1983

The rate of cardiac structural protein synthesis in perfused heart.

Synthesis of cardiac structural protein was studied in perfused rabbit hearts using [3H]lysine and perfluorochemical blood substitute. Relative synthesis rate was estimated in adult rabbit heart when both ventricles worked against zero pressure. The decreasing order was troponin complex, actinin complex, myosin, tropomyosin, and actin and was almost the same as that found in an in vivo study. The synthesis rates of myosin B in left and right ventricles were almost equal in hearts without left and right ventricular pressure load. In young rabbit heart with a right ventricular pressure load, an increase in the synthesis rate of right ventricular myosin B was observed along with the concomitant increase in that of left ventricle. As those increases were blocked by neither propranolol nor verapamil, it was suggested that these increases were not mediated by Ca2+ influx or beta-adrenergic receptors.

Actins↗
PubMed1983

Insulin effects on protein synthesis are independent of glucose and energy metabolism.

Protein synthesis was accelerated in rat hearts that were provided insulin compared with provision of glucose or pyruvate alone or a mixture of glucose and pyruvate. The faster synthetic rates were accompanied by a reduction in numbers of ribosomal subunits, indicating that peptide chain initiation was accelerated relative to elongation/termination. In hearts supplied glucose, 65% of the maximal effect on protein synthesis was achieved by addition of 1.7 X 10(-10) M insulin, but significant effects on glucose uptake as well as on tissue contents of glucose 6-phosphate and creatine phosphate were obtained only with 7 X 10(-10) M insulin. Addition of glucose to perfusates containing pyruvate did not accelerate protein synthesis, although the glucose 6-phosphate content was raised. Similarly, the stimulatory effects of insulin on protein synthesis in hearts supplied pyruvate did not depend on changes in glucose 6-phosphate content, creatine phosphate/creatine, ATP/ADP, or adenylate energy charge. These studies indicate that insulin accelerated peptide-chain initiation and protein synthesis in rat heart by mechanisms independent of the hormone's effect on glucose or energy metabolism.

Adenine Nucleotides↗
PubMed1982

Metabolism of cardiac structural proteins in normal and hypertrophied rabbit heart.

In an attempt to elucidate the characteristics of the metabolic response of the hypertrophying heart, the rates of amino acid incorporation into cardiac structural proteins were studied in female rabbit hearts in vivo by use of a pulse-label isotope (3H-lysine) method. Hypertrophy of the left ventricle was produced by applying mild aortic constriction. Structural proteins were separated from the heart excised 24 h after the pulse, and the rate of 3H incorporation was calculated as cpm. 3H/mg lysine of the protein. In the control (without aortic constriction), left ventricular structural proteins exhibited the following relative incorporation rate (the rate in actin being taken as 1.0): native tropomyosin, 2.79 +/- 0.38 (mean +/- SE, n = 5); 10S-actinin and alpha-actinin complex, 2.52 +/- 0.29; heavy chain of myosin, 2.09 +/- 0.25; light chain of myosin, 1.82 +/- 0.28; soluble protein, 1.79 +/- 0.30; and actin, 1.0. In the rabbits with aortic stenosis the rates of amino acid incorporation showed a striking increase up to 7 days after surgery, and declined to the control level by 1 month. Among the protein fractions, native tropomyosin and the light chain of myosin showed a much higher rate of isotopic incorporation during the earlier phase of the response. These results seem to indicate the presence of a unique pattern of metabolic response in cardiac muscle confronted with a workload.

Amino Acids↗
PubMed1980

Actomyosin extracted from bovine aortic intima.

Actomyosin extracted from bovine aortic intima with a KCl-ATP medium of low ionic strength, but not with a KCl medium of high ionic strength, exhibited Ca2+ sensitivity. Aortic medial actomyosin extracted with a medium of high ionic strength retained the Ca2+ sensitivity. These differences in extractability suggest that actomyosin of the aortic intima is different from that of the aortic media.

Actomyosin↗
PubMed1980

Turnover rates and synthesis of cardiac structural proteins in normal and hypertrophied heart.

Turnover rates and synthesis of cardiac structural proteins were studied in normal and hypertrophied rabbit heart. The order of incorporation rates of radioactive lysine in normal heart was: left ventricular greater than right ventricular greater than atrial greater than skeletal myosin B. In left ventricular muscle, the order of relative turnover rates of structural proteins was: native tropomyosin greater than the complex of 10 S-actinin and alpha-actinin greater than myosin heavy chain greater than myosin light chain greater than (soluble protein) greater than actin. After aortic constriction (to three-fourths of its original circumference), the rates of incorporation of radioactive lysine into each structural protein fraction increased, reaching a peak on the 7th day. The values returned to the levels of the normal group after 1 month. It was noted that the increase of incorporation into native tropomyosin was greater than the other structural proteins 7 days after constriction.

Actinin↗
PubMedDate not supplied

Factors determining the utilization of glucose in isolated rat hearts.

Glucose utilization by the isolated rat heart is restricted by flux through the membrane transport, phosphofructokinase and glyceraldehyde-3-P dehydrogenase reactions. These reactions can be accelerated by hormones, such as insulin, by mechanical factors, such as the "garden-hose effect", heart rate, and perhaps ventricular pressure development, and by oxygen deprivation. Glucose utilization is restricted by provision of exogenous non-carbohydrate substrates and by utilization of endogenous substrate stores. Isolated hearts perfused as Langendorff preparations with or without a ventricular drain, working hearts, and ischemic preparations are useful in defining rate-limiting steps and mechanisms of regulation. However, when glucose is supplied as the sole exogenous substrate, its rates of utilization do not reflect the more complex in vivo situation where competing substrates such as fatty acids are preferentially utilized.

Adenosine Triphosphate↗
PubMedDate not supplied

A study of the normal values and habituation phenomenon of sympathetic skin response.

Sympathetic skin response (SSR) has been developed recently as a method of capturing the autonomic nerve response as a parameter of the sweat gland function. In this study, our aim was to obtain the normal values with regard to both amplitude and latency of SSR from 50 healthy subjects and to find out the habituation mode, which is one of the most characteristic phenomena of SSR. The measurements were recorded from the hand and foot by rectangular waveform electric stimulation. The correlation coefficient regarding hand and foot leads, amplitude, and latency were studied at normal values. The result was that no significant difference could be observed between the left and right leads with regard to amplitude and latency recorded from the hand and foot leads. However, between hand and foot leads, a significant difference was observed for both latency and amplitude. As for the habituation, electric stimulations were also applied to 20 healthy subjects (age range, 21-62 yr) in the same manner as that used in taking the normal values. For the latency and amplitude of the response in association with the stimulation trials (Rn), the mean values of the hand as well as the foot were determined by averaging the values recorded from both hands and both feet of the 20 subjects. These values were designated as the latency and the amplitude of the hand and foot from R1 to R15. The changes observed in response to the transition in the number of stimulations were statistically evaluated as a gradual decrease in the amplitude. This phenomenon is thought to be a result of learning. On the basis of the 15 consecutive stimulations, a decrease in amplitude to the 7th and 8th stimulations and constancy in the results thereafter was observed, although minor differences in the results were apparent between the hand and foot leads.

Adult↗