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Biomedical subjects

W K Ho

Publications and source records attributed to W K Ho.

At least 109 records · Page 6Linked to original sources
PubMed1991

Cloning of trichosanthin cDNA and its expression in Escherichia coli.

Several cDNA clones coding for trichosanthin (TCS) have been isolated from a cDNA library prepared from the poly(A)+RNA of the root tuber of Trichosanthes kirilowii Maximowicz. The nucleotide sequence codes for a protein of 289 amino acids (aa) including a putative signal peptide of 23 aa and an extra 19 aa at the C terminus; the latter two have not been found in TCS obtained from the natural product [Collins et al., J. Biol. Chem. 265 (1990) 8665-8669]. Recombinant TCS (reTCS) was synthesized in Escherichia coli, in which the cDNA without the signal sequence was expressed under the control of the trc promoter; reTCS was detected by a rabbit anti-TCS antiserum.

Amino Acid Sequence↗
PubMed1990

Inward current generated by Na-Ca exchange during the action potential in single atrial cells of the rabbit.

To investigate the underlying ionic mechanism of the late plateau phase of the action potential in rabbit atrium the whole-cell patch-clamp technique with intracellular perfusion was used. We recorded the inward current during repolarizations following a brief 2 ms depolarizing pulse to +40 mV from a holding potential of between -70 and -80 mV. The development of this current coincides with the onset of the late plateau phase of the action potential. Peak activation of the current occurs about 10 ms from the beginning of the depolarizing pulse, and it decays spontaneously with a slow timecourse. Its voltage dependency from -40 mV to +40 mV shows very steep activation (-40 to -20 mV) and shows almost the same maximum magnitude between -10 mV and +40 mV. This behaviour is quite different from that of the calcium current. The inward current and the late plateau phase of the action potential were both abolished by the application of 5 mM EGTA, 1 microM ryanodine and by reducing the Na+ gradient. The fully activated current-voltage relation of the inward current was plotted as the difference current before and after treatment with Ryanodine, Diltiazem, 20 mM Na+ inside or 30% Na+ outside and shows an exponential voltage dependence with the largest magnitude of the current occurring at negative potentials. The current-voltage (I-V) curve was well fitted by the Na-Ca exchange equation, i = A exp (-(1 - r)EF/RT). The results suggest that the inward current contributes to the generation of the late plateau phase of the rabbit atrial action potential, and is activated by intracellular calcium released from the sarcoplasmic reticulum. Sarcoplasmic reticulum calcium release appears to be triggered both by the membrane voltage and by the calcium current. It is concluded that the inward current is generated by Na-Ca exchange.

Action Potentials↗
PubMed1989

Cloning of the grass carp growth hormone cDNA.

We have constructed a cDNA library in lamda gt11 using mRNA isolated from the pituitary glands of the grass carp (Ctenopharyngodon idellus). Based on the published sequence of the rainbow trout growth hormone cDNA, we synthesized two oligonucleotide probes. One of these hybridized strongly with a specific mRNA fragment from the grass carp pituitary. Using this probe, we have isolated six positive clones carrying an insert of approximately 1.2 Kb. By restriction enzyme digestion, all the clones were determined to be identical. Sequence determination on one of them indicated that it has an open reading frame coding for 210 amino acids. Both the nucleotide and translated amino acid sequence are highly homologous to those of the salmon growth hormone and the common carp. A putative signal peptide consisting of hydrophobic amino acids can be identified at the 5' end of the sequence. A polyadenylation signal, ATTAAA, was also present 12 base upstream from the poly A tail.

Amino Acid Sequence↗
PubMed1989

Opioid-like activity in the cerebrospinal fluid of pain patients treated by electroacupuncture.

Thirteen patients with pain from various causes were treated by electroacupuncture for 30 min. Cerebrospinal fluid (CSF) was obtained before and after treatment. Opioid-like substances in the CSF were fractionated by high pressure liquid chromatography and assayed by competitive receptor binding using a mu-specific radioligand, [D-ala2, MePhe4, gly-ol5]-enkephalin (DAGO). Opioid activity, associated with a fraction, eluted at 18-20% acetonitrile, consistently showed an increase in level after acupuncture. Two other fractions eluted at larger concentrations of acetonitrile also increased significantly after acupuncture; however the increase was not consistently observed in every patient. Measurements of beta-endorphin and dynorphin by radioimmunoassay indicated that 80 and 60% of the patients, respectively, had a higher level of these peptides after acupuncture. The nature of the opioid activity, eluted at 18-20% acetonitrile is unknown; however a small amount of it could be found in various parts of the brain of rat.

Chromatography, High Pressure Liquid↗
PubMed1989

Tetramethylpyrazine for treatment of experimentally induced stroke in Mongolian gerbils.

Tetramethylpyrazine, a drug originally isolated from the rhizome of Ligusticum walliichi, has been used routinely in China for the treatment of stroke and angina pectoris. We evaluated this drug by testing its effectiveness in increasing the survival rate in a stroke model using Mongolian gerbils. Our results indicate that tetramethylpyrazine can increase survival rate only if it is administered before the induction of cerebral ischemia. Since we administered the drug intraperitoneally, it is possible that pretreatment was necessary to increase its effective concentration in the blood. Receptor binding studies indicated that tetramethylpyrazine was inactive against a variety of pharmacologically active receptors.

Animals↗
PubMed1986

Suppression of immunological functions in morphine addicted mice.

Lymphocytes isolated from morphine addicted mice show a number of impaired immunological functions. They include Con A stimulated mitogenesis, NK cell activity, plaque forming cell activity and delayed-type of hypersensitivity. In addition, the met-enkephalin and beta-endorphin level in the lymph nodes of addicted mice were also depressed.

Animals↗
PubMed1984

Comparison of the effectiveness of different opioid peptides in suppressing heroin withdrawal.

The effectiveness of beta-endorphin, dynorphin-(1-13), dynorphin-(1-10) amide, alpha-neoendorphin and [D-Ala2,D-Leu5]enkephalin in suppressing withdrawal in heroin addicts was compared in this study. Groups of six patients were stabilized overnight in the hospital and were treated with either saline or peptide when withdrawal symptoms began to appear the following morning. Withdrawal was scored before and after treatment by the patient himself and an independent observer. Peptides were administered in a bolus dose of 60 micrograms/kg body weight. The patient, the observer and the physician who administered the injection were all blind to the nature of the compound given. All treatments, including those with saline, produced an overall reduction of withdrawal score. However, by statistical analysis, only treatments with beta-endorphin, [D-Ala2,D-Leu5]enkephalin and dynorphin-(1-13) were effective in producing a significant decrease of withdrawal symptoms. The length of relief brought about by the different peptides varied from less than an hour to a maximum of 5 h in one case. The average period of relief brought about by beta-endorphin, dynorphin-(1-13) and [D-Ala2,D-Leu5]enkephalin was 44, 46 and 60 min, respectively. Of the five peptides administered [D-Ala2,D-Leu5]enkephalin produced the largest number of side-effects.

Adult↗
PubMed1984

Brain and pituitary beta-endorphin levels at different developmental stages of the rat.

beta-Endorphin-like immunoreactivity in whole brains of Sprague-Dawley rat fetuses of different gestational ages was measured by radioimmunoassay and found to increase throughout the gestational period studied. The immunoreactivity in various brain parts (forebrain, midbrain, hindbrain, hypothalamus and pituitary) of late prenatal, early postnatal, young mature and retired breeder rats was also determined. In all the brain parts studied, a maximum in the content and concentration of beta-endorphin-like immunoreactivity was attained when the rats were about 3-4 months old.

Aging↗
PubMed1983

Cerebrospinal fluid [Met5]enkephalin level in schizophrenics during treatment with naloxone.

The effect of naloxone on CSF [Met5]enkephalin level and on the suppression of psychotic symptoms associated with schizophrenia was studied. Seven patients were treated with naloxone at a dose of 0.4 mg/day for seven days and six were treated with saline for the same period. Of the seven patients receiving naloxone, three showed signs of improvement. In the saline group, only one case of obvious improvement was observed. The mean CSF [Met5]enkephalin level before and after treatment in both the naloxone and saline group did not change significantly. However, there was a highly significant correlation (r = -0.73, P less than 0.01) between the increase of [Met5]enkephalin level and the decrease in psychotic symptoms.

Adult↗
PubMed1983

Met-enkephalin level in the cerebrospinal fluid of schizophrenic patients.

The level of met-enkephalin in the cerebrospinal fluid of 18 schizophrenic and 18 non-mental patients were determined by radioimmunoassay. The concentration of this peptide in the schizophrenic patients ranged from 12 to 39 ng/l with a mean of 22.2 ng/l. The mean and range of the non-mental patients were 28 ng/l and 16 to 41 ng/l, respectively. The difference between the mean enkephalin level of the two groups was statistically significant by the t-test. However, this difference must be interpreted with caution since the data obtained from the non-mental patients cannot be regarded as normal. No significant correlation was observed between the severity of schizophrenic symptoms and cerebrospinal fluid met-enkephalin level.

Enkephalin, Methionine↗
PubMed1983

Activation of low density lipoprotein receptor synthesis by treatment with partially delipidated low density lipoprotein.

The role of apo-low density lipoprotein in the regulation of low density lipoprotein receptor synthesis was studied. Fibroblasts preincubated in the presence of a cholesterol-free low density lipoprotein preparation showed an increase of 50% in receptor activity. In contrast, when cells were preincubated with a similar amount of normal low density lipoproteins a 2- to 3-fold decrease of receptor activity was observed. The increase of receptor activity induced by delipidated LDL was probably due to an increase of synthesis rather than an unmasking effect since treatment with puromycin essentially abrogated the activation. The ability of the partially delipidated low density lipoproteins to elicit receptor synthesis could not be accounted for by a depletion of cellular cholesterol because a similar preparation of delipidated high density lipoproteins was unable to induce receptor synthesis but was able to reduce cellular cholesterol to the same extent. Treatment with chloroquine, a lyzosome inhibitor, blocked the ability of the delipidated low density lipoprotein to activate receptor synthesis. This suggests that degraded fragments rather than the intact delipidated lipoprotein are necessary to trigger the cell to synthesize more receptors.

Cells, Cultured↗
PubMed1982

Suppression of withdrawal symptoms by dynorphin in heroin addicts.

The effectiveness of dynorphin-(1-13) in suppressing heroin withdrawal was studied. At a dose of 60 micrograms/kg body weight, dynorphin-(1-13) was effective in suppressing withdrawal symptoms. When saline was administered a strong placebo effect was noticed that, however, did not influence the outcome of the results. Only three out of the twelve patients receiving dynorphin-(1-13) experienced some mild side-effects such as feeling warm, dizziness and precordial formication.

Adult↗
PubMed1982

Reduction of opioid binding in neuroblastoma x glioma cells grown in medium containing unsaturated fatty acids.

Neuroblastoma x glioma cells NG108-15 were cultured in lipid-free medium supplemented with fatty acids of various chain length and unsaturation. Binding of 3H-labelled [DAla2]-[DLeu5]-enkephalin by membranes of cells grown in saturation fatty acids of different chain length was not significantly different from that of the control On the other hand, a proportional decrease of binding capacity with no change in residual receptor affinity was noticed when cells were cultured in medium containing fatty acids of increasing unsaturation. This decrease was time dependent and reached a maximum at about 48 h. Binding of [3H]dihydromorphine and [3H]naloxone was similarly affected. In contrast, when membranes of cells grown in normal medium were preincubated up to 3 h with unsaturated fatty acid and tested for opioid binding, no significant reduction was observed. Examination of the fatty acid composition of phospholipid from cells grown in linolenate indicated that a significant alteration of the acyl composition has occurred. To evaluate the underlying cause of this type of inhibition, the effect of linolenic acid on cell growth and protein synthesis was examined. When cells were cultured in 100 microM of this fatty acid, both growth and protein synthesis were retarded by 28% and 19%, respectively. Since opiate receptors are proteineous in nature, a reduction of protein synthesis may partially account for the loss of opioid binding activity. On the other hand, an increase of membrane fluidity is known to affect a number of cellular functions, including ligand-receptor recognition. Whether this can offer a satisfactory explanation for our observations remains to be established.

Animals↗
PubMed1982

Ontogenesis of opiate binding sites and radioimmunoassayable beta-endorphin and enkephalin in regions of rat brain.

The postnatal changes in the levels of radioimmunoassayable enkephalin and beta-endorphin, as well as the densities of [3H]methionine-enkephalin and [3H]naloxone binding sites in rat cerebellum, brainstem and whole forebrain were determined. The opiate peptides and the opiate binding sites reached their highest levels at the first week postpartum in the cerebellum, at the second week in the brainstem and at the third week in the whole forebrain. This finding is in line with the developmental profiles of other well-established neuronal pathways which also showed a caudal-to-rostral sequence of development. Moreover, there was a close relationship between the elevation and decline in the amounts of opiate binding sites and in the levels of opiate peptides in each brain region. These observations are consistent with other evidence which suggests that enkephalin and beta-endorphin are functioning as neurotransmitters or neuromodulators in the central nervous system.

Aging↗