Biomedical subjects

M Horiuchi

Publications and source records attributed to M Horiuchi.

352 records · Page 20Linked to original sources

PubMedDate not supplied

Characterization of human wild-type and mutant argininosuccinate synthetase proteins expressed in bacterial cells.

Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric structure composed of identical subunits. Citrullinemia is an autosomal recessive disease caused by a deficiency of ASS. We have previously identified 20 mutations in ASS mRNA of human classical citrullinemia. However, it is difficult to evaluate the effects of each mutation on the enzyme structure and function, since most of the patients are compound heterozygotes. In the present study, wild-type ASS and 12 mutant ASSs were expressed with a bacterial expression system and analyzed enzymologically and immunochemically. The properties of the purified recombinant protein with wild-type human ASS showed good agreement with native enzyme purified from human liver. Mutant ASS proteins with an expected molecular mass, except for delta 7b/Ex16, were highly expressed in the bacterial cells. It was difficult to extract ASS proteins with some mutations (A118T, delta Ex7, R157H, R363W, R363L, G390R and ins37b/Ex15&16) from cells by freezing and thawing. Extractable mutant proteins were as follows: G280R mutant was extracted with an amount of ASS protein similar to wild-type but with no ASS activity, and A192V, R272C and R304W mutants detected various amounts of ASS protein (13, 110 and 33% of wild-type, respectively) with a low ASS activity and abnormal kinetics. Higher Km values for citrulline were obtained in mutant ASSs with A192V (15 mmol/1), R272C (4.2 mmol/l) and R304W. (190 mmol/l) than in wild-type ASS (0.056 mmol/l). The results confirm that these mutations are responsible for ASS deficiency and also indicate that these amino acid residues are important for the function and structure of ASS protein.

Amino Acid Sequence↗

PubMedDate not supplied

Cricothyroid muscle in respiration.

Although the phonatory activity of cricothyroid muscle is well-known, its respiratory role often remains unrecognized. Recent data suggest this muscle plays a major role in the overall regulation of breathing by its control of expiratory resistance and flow. Cricothyroid contraction in expiration results in vocal elongation increasing glottic size. Such a mechanical effect reduces airway resistance and shortens expiratory duration. By such a mechanism, the rate of respiration may ultimately be modified using the larynx as the principal effector of this control. In this regard, cricothyroid expiratory activity is a pressure-sensitive evoked response influenced by afferent vagal stimuli. Its activity is triggered by a critical threshold of pressure-increase with respect to time, and its duration is directly dependent on the duration of positive subglottic pressure. The threshold of cricothyroid activation is reduced in hypercapnia and elevated in hypocapnic states.

Animals↗

PubMedDate not supplied

Vocal cord positioning by selective denervation. Old territory revisited.

Vocal cord positioning produced by selective laryngeal denervation remains a controversial issue in clinical laryngology. Previous studies fail to arrive at uniform conclusions for two important reasons: 1) failure to mark a reference sagittal plane from which to assess the degree of vocal cord lateralization, and 2) failure to recognize the influence of tracheostomy and respiratory positioning of the vocal cords. The present study makes use of photographic and electromyographic documentation in the assessment of the paralyzed cord. Physiologic inactivation of the cricothyroid muscle by tracheostomy is a key determinant of the lateralized cord observed in acute low vagal and recurrent nerve paralysis. Tracheostomy-related cricothyroid inactivation cannot be ignored as a major determinant of cord positioning in paralysis and should not be overlooked in determining the neuroanatomic site of injury.

Animals↗

PubMedDate not supplied

Application of a drug delivery system to a steroidal ophthalmic preparation with lipid microspheres.

The applicability of a drug delivery system to an ophthalmic preparation was examined using lipid microspheres containing hydrocortisone 17-butyrate 21-propionate (HBP). A 3H-labelled HBP ophthalmic suspension and 3H-labelled HBP lipid microspheres were applied to rabbit eyes, which were then enucleated at fixed intervals to determine the level of 3H-labelled HBP in ocular tissues. The lipid microspheres were shown to deliver the drug to the anterior ocular tissues more effectively than the ophthalmic suspension. It is suggested that a lipid microsphere ophthalmic preparation of various lipophilic drugs including steroids may be useful as a drug delivery system for ophthalmic therapy.

Administration, Topical↗

PubMedDate not supplied

Molecular and cellular mechanism of angiotensin II-mediated apoptosis.

It is well known that angiotensin II exerts growth promoting effects via the angiotensin II type 1 (AT1) receptor. We have cloned a second type of angiotensin II receptor (AT2 receptor) and demonstrated that this receptor acts as an antagonistic receptor against the AT1 receptor. Moreover, we have demonstrated that the AT2 receptor exerts growth inhibitory and proapoptotic effects by antagonizing the effects of the AT1 receptor and growth factors in several cell lines including vascular smooth muscle cells, cardiomyocytes, neuronal cell (PC12W) and fibroblasts (R3T3). We observed that the AT2 receptor activates tyrosine phosphatase(s) such as mitogen-activated protein (MAP) kinase-phosphatase-1 (MKP-1) and inactivates MAP kinase (extracellular signal-regulated kinase (ERK1 and ERK2)), resulting in Bcl-2 dephosphorylation and up-regulation of Bax. This inactivation of ERK is mediated via Gi protein coupling through its unique intracellular third loop. Moreover, we have demonstrated that interferon regulatory factor (IRF)-1 also up-regulates the AT2 receptor in apoptotic cells, suggesting that the cytokines may play an important role in angiotensin-regulated apoptosis.

3T3 Cells↗

PubMedDate not supplied

The signaling pathway of cardiotrophin-1 is not activated in hypertrophied ventricles of carnitine-deficient juvenile visceral steatosis (JVS) mice.

Cardiotrophin-1 (CT-1) is a novel cytokine which is involved in the growth and survival of cardiac cells. We examined whether CT-1 plays a role in the development of cardiac hypertrophy in carnitine-deficient juvenile visceral steatosis (JVS) mice. The CT-1 mRNA level was quantitatively measured by the competitive RT-PCR method. In contrast to other models including spontaneously hypertensive rats, CT-1 mRNA in the ventricles of JVS mice was comparable to the control at 5 days and was less than half the control value at 2 and 8 weeks when the ventricles of the JVS mice were highly hypertrophied. There were no significant differences in CT-1 mRNA levels in the lung, liver, kidney, small intestine and skeletal muscle between the JVS and control mice at 2 weeks. We did not find any difference between JVS and control mice at 2 weeks in the mRNA level of ventricular leukemia inhibitory factor (LIF) which binds to the same receptor as CT-1. Furthermore, almost no phosphorylated STAT3 (signal transducer and activator of transcription 3), downstream of the LIF receptor and the gp130 signaling subunit, was observed in the ventricles of JVS and control mice. These data show that the CT-1 signaling pathway does not play a significant role in the development of cardiac hypertrophy in JVS mice. Furthermore, we could not detect any differences in insulin-like growth factor I and II mRNA levels. All these data suggest distinct differences in the mechanisms of cardiac hypertrophy between JVS mice and other model animals.

Animals↗

PubMedDate not supplied

Effects of dilevalol and propranolol on hemodynamics in patients with essential hypertension.

Eighteen patients with essential hypertension received 50 to 200 mg of dilevalol or 60 to 90 mg of propranolol daily for six weeks. Mean arterial blood pressure and venous pressure were significantly reduced in the dilevalol-treated patients at six weeks but were unchanged in the propranolol-treated patients. The cardiac index and systemic vascular resistance remained unchanged in the dilevalol group, but were significantly reduced (cardiac index) or increased (systemic vascular resistance) in the propranolol group. No changes in heart rate were noted in either treatment group. It is concluded that dilevalol has some ideal features for the treatment of hypertension, but further research is needed to determine the causes of fatal hepatotoxicity reported in a few cases.

Blood Pressure↗

PubMedDate not supplied

Increase of brain ammonia after microwave irradiation and its mechanism.

Microwave irradiation at 4kW for 0.4 sec applied to the heads of mice produced an increase in brain ammonia. This increase resulted from stimulated breakdown of glutamine initiated by microwave irradiation and proceeded until freezing of the brain. Two glutamine-related enzymes, in the brain, phosphate-dependent glutaminase (assayed in the presence of 200mM phosphate) and glutamine synthetase, were inactivated by microwave irradiation in a similar fashion. On the other hand, glutaminase activity in the presence of 10mM phosphate increased. This is considered to be a probable cause of the increase in brain ammonia. The increased 10mM-phosphate glutaminase activity remained stable in the precipitate fraction even after 5% Triton X-100 treatment.

Adenine Nucleotides↗

PubMedDate not supplied

Radiographic analysis of a two-piece apatite implant: Part II. Preliminary report of 2-year observation.

Marginal bone height and bone density were evaluated for 2 years after two-piece dense hydroxyapatite implant (Apaceram) placement using standardized radiography and digital image processing. The chronological changes in marginal bone height were divided into three groups: Group I-level was constant or became higher with time; Group II-bone decreased gradually after superstructure placement; and Group III-bone decreased in height rapidly after abutment placement. Bone density around the successful Apaceram implant, especially in the crestal region, increased clearly. The results suggest that bone resorption/formation around the implant is related to occlusal stress, and that adequate occlusal stress should be exerted on the implant at each phase after the implant placement.

Adult↗

PubMedDate not supplied

In vitro study of mandibular implant-retained overdentures: the influence of stud attachments on load transfer to the implant and soft tissue.

This study investigated the occlusal stress distribution to the implant and soft tissue for the implant-retained overdenture. The stress at the molar residual ridge and the strain around the implant were measured on an experimental resin cast using static and dynamic loading. The influence of connecting structures of stud attachments on stress distribution was discussed. The occlusal stress had a tendency to concentrate on the implant, especially in the areas distal to the implant. The modified magnetic attachment system, using a silicone-covered magnet, provided the optimal stress distribution.

Bite Force↗