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Biomedical subjects

H N Kim

Publications and source records attributed to H N Kim.

50 records · Page 3Linked to original sources
PubMed1994

Synthesis and expression of a gene for the rat glucagon receptor. Replacement of an aspartic acid in the extracellular domain prevents glucagon binding.

In order to facilitate structure-function studies of the glucagon receptor by site-directed mutagenesis, we have designed and synthesized a gene for the rat glucagon receptor. The gene codes for the native 485-amino-acid protein but contains 91 unique restriction sites. To characterize gene expression, a highly specific, high affinity antipeptide antibody was prepared against the receptor. The synthetic gene was expressed in transiently transfected monkey kidney (COS-1) cells. COS cells expressing the synthetic receptor gene bound glucagon with affinity and specificity similar to that of hepatocytes containing native receptor. The transfected COS cells also showed increased intracellular cAMP levels in response to glucagon. The functional role of an aspartic acid residue in the NH2-terminal tail of the receptor was tested by site-directed mutagenesis. This site in the related growth hormone releasing factor receptor was shown to be responsible for the little mouse (lit) genetic defect that results in mice of small size with hypoplastic pituitary glands. Mutant glucagon receptors with amino acid replacements of Asp64 were expressed at normal levels in COS cells but failed to bind glucagon. These results indicate that amino acid Asp64 may play a key role in glucagon binding to receptor.

Adenylyl Cyclases↗
PubMed1994

Platelet activating factor treatment of spermatozoa enhances rabbit oocyte fertilization following subzonal sperm insertion.

PURPOSE: The objective of this study was to evaluate the effects of spermatozoal platelet activating factor (PAF) treatment on fertilization rates employing subzonal sperm insertion in the rabbit. STUDY DESIGN: Oocytes (n = 130) with distinct first polar bodies were injected with three to seven motile spermatozoa. Half (n = 65) of the oocytes were injected with PAF-treated sperm, whereas the other half (n = 65) served as controls and were injected with nontreated sperm. Fertilization rates were assessed by the formation of two pronuclei followed by cleavage to the two-cell stage. RESULTS: In the group of oocytes injected with PAF-treated sperm, we noted a significant (P < 0.001) improvement in fertilization rates, 61.5% (40/65), vs. control nontreated sperm, 20.0% (13/65). Subsequent cleavage to the two-cell stage was noted for 95% (38/40) in the treated vs 92.3% (12/13) in the nontreated fertilized zygotes. CONCLUSION: We conclude that PAF treatment of rabbit spermatozoa prior to subzonal insertion improves fertilization rates and may be of clinical significance in assisted reproductive programs.

Animals↗
PubMed1994

Embryo survival after pronuclear microinjection and trophectoderm biopsy.

OBJECTIVE: Our purpose was to compare murine embryo development after pronuclear microinjection of a gene construct, followed by trophectoderm biopsy at the blastocyst state, with development after a single micromanipulation, and with cultured controls. STUDY DESIGN: alpha-Myosin heavy-chain gene sequence was microinjected into the murine embryo pronucleus and cultured to blastocyst. After trophectoderm biopsy the embryos were allowed to re-expand. Re-expanded embryos were transferred to pseudopregnant females; implantation and live birth rates were recorded. In this study group the rates were compared with three control groups of embryos simultaneously cultured after (1) pronuclear microinjection only, (2) trophectoderm biopsy only, and (3) non-micromanipulated, culture only. RESULTS: A total of 1222 embryos were divided among the four groups. In the study group 472 embryos underwent pronuclear microinjection and trophectoderm biopsy. Of these, 203 (43%) reached the blastocyst stage and underwent biopsy; 183 (38.8%) re-expanded after biopsy. Of 275 pronuclear microinjected only (control 1) embryos, 113 (41.1%) reached the blastocyst stage. Of 336 embryos 148 (44.0%) reached the blastocyst stage and underwent trophectoderm biopsy only (control 2); 129 (39.2%) survived biopsy. The cultured only group (control 3) consisted of 139 pronuclear embryos; 67 (48.2%) developed to the blastocyst stage. CONCLUSIONS: Murine embryos can survive two micro-manipulations, pronuclear microinjection followed by trophectoderm micro-biopsy. Although there is minimal effect of these procedures on embryonic development in vitro, the live birth rate is tenuous.

Animals↗
PubMed1993

Embryonic platelet activating factor production in the rabbit increases during the preimplantation phase.

OBJECTIVE: This study measured platelet activating factor (PAF) production by rabbit embryos in vitro and ascertained if there is increased PAF production associated with advancing embryonic development. STUDY DESIGN: Two-cell rabbit embryos were recovered from superovulated New Zealand White does and cultured in vitro for 96 hr. Every 24 hr embryos were scored for developmental stage and PAF activity from the corresponding culture medium was measured by platelet aggregation and organic phosphate analyses. RESULTS: PAF was detected in culture medium at all stages from two cells to blastocysts and rose significantly (P < 0.001) at each 24-hr interval, reaching maximal levels at the expanded blastocyst stage. CONCLUSION: Maximal PAF production by expanded blastocysts may be an embryonic paracrine signal that facilitates implantation.

Animals↗
PubMed1992

Expression of heat shock protein, HSP72, in the guinea pig and rat cochlea after hyperthermia: immunochemical and in situ hybridization analysis.

The induction of the heat shock protein, HSP72, was studied in the cochlea of guinea pigs and rats subjected to a hyperthermic stress. Analyses were done by immunoblotting and immunocytochemistry at 6 and 12 h after heat shock, using a commercially available monoclonal antibody (Amersham), and by in situ hybridization 1 h after heat shock using an oligonucleotide probe. In guinea pig immunoblots of the cochlea, HSP72 was present in both unstressed and heat stressed animals and immunocytochemistry did not reveal any difference of staining between them. As opposed to guinea pig, HSP72 was not found in unstressed rat cochlea. Heat shock induced HSP72 expression in most inner ear tissues of the rat examined by immunoblotting. Immunocytochemistry and in situ hybridization localized HSP72 synthesis in ganglion neurons, Schwann cells, spiral limbus, spiral ligament and stria vascularis. The strongest immunoreactivity and highest density of silver grains were seen in the stria vascularis. All blood vessels were strongly immunoreactive and were outlined with silver grains. These results show that HSP72 synthesis can be induced by hyperthermia in rat cochlea and suggest that this protein could be a useful marker for assessment of the effects of specific stresses in this organ.

Animals↗
PubMed1992

Corrosive esophageal stricture: safety and effectiveness of balloon dilation.

The safety and long-term effectiveness of fluoroscopically guided balloon dilation for corrosive esophageal stricture was evaluated in 22 patients with a follow-up period of more than 1 year (range, 13-52 months). The average interval between corrosive agent ingestion and initial balloon dilation was 18 years (range, 2 months to 51 years). Balloons with a diameter of 5-8 mm were used in the initial attempt. The caliber of the balloon catheter was increased gradually over subsequent dilations, up to a diameter that allowed patients to swallow solid foods. Dilation of more than 17 mm in diameter was performed in five patients. Patients underwent one to five sessions. Esophageal rupture occurred in seven patients and was treated nonoperatively in five and surgically in two. With exclusion of these latter two, 11 of 20 could tolerate swallowing all kinds of food and nine could tolerate swallowing most foods. Balloon dilation in corrosive esophageal strictures is effective, but the high rupture rate indicates the need for extra caution.

Acetates↗
PubMed1992

Comparison of speech recognition ability with different speech processing strategies by Korean cochlear implantees.

Many variables affect the audiologic performance of cochlear implantees. With current methods of evaluation, it is difficult to directly compare auditory function with different speech coding strategies. We compared the audiologic performance directly with F0F1F2 and multipeak speech coding strategies in the same implanted ear of eight Korean cochlear implantees. We tested word and phoneme recognition abilities using Korean word lists for speech audiometry and two-syllable nonsense words, respectively. With the multipeak coding strategy, a significant difference in discrimination ability was found in the initial fricative consonant phonemes (/s/,/ss/,/h/). Our results suggest that the improvement of speech recognition ability with the multipeak coding strategy comes primarily from the better understanding of the initial fricative consonants.

Adult↗
PubMed1991

Identification and ultrastructural localization of a calretinin-like calcium-binding protein (protein 10) in the guinea pig and rat inner ear.

Calretinin has been identified as a brain specific calcium-binding protein which appears as a prominent protein in the cochlear nucleus. We identified and localized calretinin in the guinea pig and rat inner ear using polyclonal antibodies. Immunoblot analyses of guinea pig and rat auditory nerve homogenates revealed an immunoreactive band migrating with the same molecular weight as the purified protein, at Mr = 29 k. Immunocytochemistry was carried out at the light and electron microscope levels. In the guinea pig cochlea, inner hair cells, Deiters' cells, Hensen's cells and interdental cells of the spiral limbus were stained. Most of the cochlear ganglion cells were immunostained. In the guinea pig vestibular organs, the staining was exclusively neuronal and localized in large nerve fibers and nerve calices of the apex of the cristae. Only some vestibular ganglion cells were stained. In the rat cochlea, inner hair cells and most of the ganglion neurons were immunoreactive. In the rat vestibule, large nerve fibers and calices were stained as were some type II hairs cells. Only some vestibular ganglion cells were reactive. Electron microscopic observations of immunostained guinea pig cochlea and vestibule showed that the staining was cytosolic. In addition, specific sub-localization was also found in the apical portion of the nerve calices in association with microvesicles. These results describe the discrete localization of calretinin in the cochlea and in the vestibular receptors and suggest a function associated with biochemical regulations at the level of microvesicles in vestibular afferent neurons.

Animals↗
PubMed1990

Variability of the surgical anatomy of the neurovascular complex of the cerebellopontine angle.

The variability of the anatomic relationship of the anterior inferior cerebellar artery (AICA) to the facial (seventh) and vestibulocochlear (eighth) nerves was studied in 52 cerebellopontine angles (CPAs) from 26 adult cadavers. The AICA originated from the basilar artery (98.1%) or from the vertebral artery (1.9%) as a single (92.3% of CPAs) or duplicate (7.7%) artery. Each of the 52 CPAs had one or more arterial trunks that coursed in close proximity to the seventh and eighth cranial nerves and thus were said to be nerve-related. The nerve-related arterial trunks were divided into three segments based on their relationship to the nerves and meatus: the premeatal, meatal, and postmeatal segments. The nerve-related branches of the AICA gave rise to the internal auditory artery in 92.3% of the CPAs, the recurrent perforating artery in 78.8%, and the subarcuate artery in 30.8%. The importance of understanding the surgical anatomy of the neurovascular complex of the CPA when performing a vestibular neurectomy is reviewed.

Adult↗
PubMed1989

Hazard from weapons impulses: histological and electrophysiological evidence.

Current methods of rating the hazard of weapons impulses for the ear have recently been challenged by electrophysiological data from experiments with animal ears which indicate that the hazard from low-frequency impulses is much lower than the hazard from higher frequency impulses (Dancer et al., 1981; Price, 1986b). To supplement these data, histological data are reported here for 51 cats that were exposed on one occasion to either rifle or howitzer impulses at peak pressures from 145 to 155 dB or 153 to 166 dB, respectively. Histological procedures (scanning electron and light microscopy) were carried out over 2 months after the exposure and after electrophysiological measures had been made. For both types of impulse the losses tended to be in the middle of the cochlea in focused lesions, even though the spectral peaks of the acoustic stimuli had been at about 80 Hz (howitzer) and 1000 Hz (rifle). Outer hair cells were more susceptible than the inner hair cells and interindividual differences in effects were large. Furthermore, the two impulse sources were equally hazardous when the peak pressure of the rifle impulse was lower than the peak pressure of the howitzer impulse by about 9 dB. In terms of A-weighted energy, the exposures were equally hazardous when the rifle exposure contained about 35 times less energy than the howitzer exposure. The histological data are thus consistent with the electrophysiological data, which indicate that present standards for impulse noise exposure may overrate the hazard of low-frequency impulses relative to impulses in the midrange.

Animals↗
PubMedDate not supplied

Platelet-activating factor production from in vitro and in vivo fertilized murine embryos is similar.

PROBLEM: This study measured platelet-activating factor (PAF) production of in vitro and in vivo fertilized murine embryos to ascertain whether site of fertilization impacted subsequent embryonic PAF production. METHOD: Oocytes and embryo were collected from stimulated B6D2F1 mice. PAF production throughout the preimplantation phase from the two-celled stage through expanded blastocysts was measured and compared among normally developing embryos with the only difference being site of fertilization. RESULTS: A striking increase in PAF production was noted for both in vivo and in vitro fertilized embryos over the four days of culture. Significantly higher (P < .001) levels of PAF production were noted with development from the two-celled stage (47.22 +/- 4.13; 44.30 +/- 2.43) to expanded blastocysts (254.31 +/- 24.01; 255.11 +/- 5.35 ng/embryo/24 h) for both in vitro and in vivo fertilized embryos, respectively. There was no significant difference (P > .05) in PAF production between the two groups of embryos. CONCLUSIONS: Embryonic PAF production in the mouse increases in a stage-specific manner, and specifically the site of fertilization in vitro versus in vivo does not affect PAF production in normally developing embryos.

Animals↗