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Biomedical subjects

C L Ho

Publications and source records attributed to C L Ho.

At least 91 records · Page 5Linked to original sources
PubMed1987

Beta-endorphin: peripheral opioid activity of homologues from six species.

The peripheral opioid activity of six homologous beta-endorphins (beta-EPs) were assayed on the guinea pig ileum and the vas deferens of the mouse, the rat and the rabbit. In the guinea pig ileum assay, human beta-EP (beta h-EP) was less potent than camel, turkey, and ostrich beta-EPs, of the same potency as equine beta-EP and more active than des-acetyl salmon beta-EP. In the rat vas deferens, mammalian beta-EPs showed higher activity than those from the bird and the fish, whereas in the mouse vas deferens assay, beta h-EP is more active than those from other species. In the rabbit vas deferens, however, all homologous beta-EPs show very weak activity. The relative potency of beta-EP homologues obtained from rat vas deferens assay is in good correlation with the analgesic potency, while the receptor binding activity does not correlate with any of the four bioassays, but appears to be related to the charge properties of the peptides.

Amino Acid Sequence↗
PubMed1986

Hornetin: the lethal protein of the hornet (Vespa flavitarsus) venom.

By gel permeation on a Fractogel TSK HW 50 column followed by ion-exchange chromatography on carboxymethylcellulose CM 52, a lethal protein, designated hornetin, was purified from the venom of Vespa flavitarsus. Hornetin is a highly basic protein (pI 10.2) with a molecular mass of about 32 kDa. Its amino acid composition is characterized by a high content of lysine, aspartic and glutamic acid, and is devoid of tryptophan and cysteine. The lack of cysteine in the molecule is distinct from other known vespid venom proteins of comparable size. The i.v. LD50 of the toxin is 0.42 microgram per g mouse. Assayed on the red blood cells of the mouse and guinea-pig as well as isolated nerve muscle preparations of the chick and mouse, hornetin showed direct hemolytic activity and presynaptic neurotoxicity at microgram level and displayed musculotropic effect at higher concentrations.

Acetylcholine↗
PubMed1986

The role of enzyme activity and charge properties on the presynaptic neurotoxicity and the contracture-inducing activity of snake venom phospholipases A2.

Two toxic phospholipases A2, caudoxin from Bitis caudalis venom and the basic phospholipase A2 from Naja nigricollis venom, were selected for a study of the contribution of enzyme activity and charge properties to the presynaptic neurotoxicity and the contracture-inducing activity of the enzyme. Reducing catalytic activity by lowering the incubation temperature or by substitution of Sr2+ for Ca2+ in the bathing medium causes a significant prolongation of the time to neuromuscular block by caudoxin, but does not change the contracture-inducing activity of Naja nigricollis basic phospholipase A2. In the chick muscle pretreated with heparin, the latter enzyme fails to evoke contracture, whereas the presynaptic neuromuscular blocking action of caudoxin remains little affected. Histidine-modified Naja nigricollis enzyme, which has lost 95% of its enzyme activity, retains considerable ability to induce contracture and to abolish indirectly evoked contraction, while lysine-methylated enzyme, which loses only 10% of its enzyme activity, almost completely loses its ability to evoke muscle contracture. It is concluded that enzyme activity is important for the presynaptic effects of caudoxin, but not for the contracture-inducing action of the Naja nigricollis enzyme. In the latter enzyme certain easily methylated lysine residues are critical for its ability to induce muscle contracture.

Animals↗
PubMed1986

Differences in pharmacological actions between beta-bungarotoxin and other neurotoxic phospholipases A2 purified from snake venoms.

Five highly toxic phospholipases A2 (PLAs) (beta-bungarotoxin, caudoxin, Mojave toxin, notexin and a basic PLA from Naja nigricollis venom) were compared for their pharmacological actions. In the chick biventer cervicis nerve-muscle preparation, all PLA toxins except beta-bungarotoxin (beta-BuTX) inhibited the postsynaptic acetylcholine response and induced contracture of the muscle at a high concentration. Indirect hemolytic activity was found in all PLA toxins and some of the toxins (Naja nigricollis basic PLA and Mojave toxin) even showed a potent direct hemolytic action, while beta-BuTX was devoid of both direct and indirect hemolytic activities on the guinea-pig erythrocytes. All PLA toxins except beta-BuTX caused an increase in muscle tone in the guinea-pig ileum at a concentration as low as 0.05 microgram/ml, and an increase in the contractile force in the guinea-pig atrium at a concentration of 1.0 microgram/ml. In contrast, beta-BuTX had no stimulant effect at concentrations up to 10 micrograms/ml. On the cultured cells, beta-BuTX suppressed the proliferation of neuroblastoma cells, but did not cause lysis of non-neuronal cells of the rat brain. However, beta-BuTX uniquely maintained a high population of viable cells in the neuroblastoma cell cultures. From these results it was concluded that beta-BuTX is the most specific presynaptic neurotoxin among the PLA toxins so far tested.

Animals↗
PubMed1985

Opiate receptor binding profile in the rabbit cerebellum and brain membranes.

The equilibrium dissociation constants (Kd) and maximal binding capacities of tritiated dihydromorphine (DHM), [D-Ala2,D-Leu5]enkephalin (DADLE), ethylketocyclazocine (EKC) and human beta-endorphin (beta-EP) in rabbit cerebellum and brain membranes have been investigated. Binding of tritiated DHM and DADLE was adequately described by a single affinity class of binding sites, while that of EKC required two affinity sites. Binding of tritiated beta-EP was also consistent with a single affinity class of binding sites by Scatchard analysis, but inhibition of the binding with type selective opiate receptor ligands revealed multiple sites. Sequential displacement of a broad spectrum opiate ligand, diprenorphine (DIP), by type selective ligands showed that cerebellum membranes are relatively rich in mu (40%) and deficient in K (12%) binding sites, while brain membranes are relatively rich in K (32%) and deficient in mu (12%) binding sites. beta-EP displaces 88 and 73% of tritiated DIP from cerebellum and brain membranes, respectively, suggesting multiple sites of beta-EP binding.

Animals↗
PubMed1985

Beta-endorphin. Biological activity of synthetic analogs with analgesia inhibiting property in rat vas deferens and guinea pig ileum assays.

Three synthetic analogs of human beta-endorphin (beta h-EP) (I, [Gln8, Gly31]-beta h-EP-Gly-Gly-NH2; II, [Arg9,12,24,28,29]-beta h-EP and III, [Cys11,26, Phe27, Gly31]-beta h-EP), which have been shown to possess potent inhibiting activity to beta h-EP-induced analgesia, were assayed in rat vas deferens and guinea pig ileum bioassay systems. In the rat vas deferens assay, relative potencies of these analogs were beta h-EP, 100; I, 30; II, 40; III, 1, whereas in the guinea pig ileum assay: beta h-EP, 100; I, 184; II, 81; III, 163. From previous studies on their analgesia potency in mice and opiate receptor-binding activity in rat brain membranes, their activity in rat vas deferens correlates well with the analgesic potency and the activity from guinea pig ileum assay shows good correlations with that from the opiate receptor-binding assay.

Analgesia↗
PubMed1984

Presynaptic and musculotropic effects of a basic phospholipase A2 from the Formosan habu (Trimeresurus mucrosquamatus) venom.

A basic phospholipase A2 purified from the venom of a crotalid snake (Trimeresurus mucrosquamatus) was applied to chick and mouse neuromuscular preparations. The enzyme at lower concentrations (1-3 micrograms/ml) blocks neuromuscular transmission at a presynaptic site, while at higher concentrations (10-30 micrograms/ml) it causes contracture and depolarization of the muscle as well. It is concluded that the mode of action of the enzyme on vertebrate nerve-muscle transmission is similar to that of notexin and ceruleotoxin from elapid snake venoms.

Animals↗
PubMed1984

One-stage reconstruction of the penis with free skin flap: report of three cases.

Three cases of penile defect of varying extent were reconstructed with free skin flaps from the forearm based on the radial artery. In two cases, part of the forearm flap was used to reconstruct the urethra, and the rest of the flap to reconstruct the corpus penis. A piece of autogenous cartilage was then inserted between the two layers. All procedures were completed in a one-stage operation. In the third case, a free skin graft was used for urethral reconstruction. Surgery in all three cases was successful, providing a penis of acceptable appearance as well as excellent urinary function.

Adult↗
PubMed1984

Adrenocorticotropin. 57. Synthesis and biological activity of ostrich and turkey hormones.

Synthesis of ostrich and turkey corticotropin (ACTH) has been accomplished by the solid-phase method. Each was identical to the natural hormone in high performance liquid chromatography. Relative potencies in a lipolytic assay in isolated rabbit fat cells were: human ACTH, 100; ostrich ACTH, 53; turkey ACTH, 28. In isolated rat fat cells relative lipolytic potencies were: human ACTH, 100; ostrich ACTH, 2; turkey ACTH, 13. It was concluded that lipolytic potency is sensitive to alterations in structure throughout the entire length of the ACTH sequence in the rat fat cell assay.

Adipose Tissue↗
PubMed1983

beta-endorphin: characteristics of binding sites in the rabbit cerebellar and brain membranes.

Specific binding of human beta-endorphin to rabbit cerebellar and brain membranes was measured using [3H2-Tyr27]-beta h-endorphin as the primary ligand. In both tissues binding was time dependent and saturable, with apparent equilibrium dissociation constants of 0.275 nM and 0.449 nM in the cerebellum and brain, respectively. The binding capacity of cerebellum is greater than that of brain. Kinetic studies showed that the association rate constants were 2.7 X 10(7) M-1min-1 for cerebellum and 2.4 X 10(7) M-1min-1 for brain. Dissociation of tritiated beta h-endorphin from both cerebellum and brain is not consistent with a first order decay from a single site. In the cerebellum there is a time-dependent increase in slowly dissociating complex. The potency of several opioid peptides and opiates to inhibit the binding of tritiated beta h-endorphin was determined. Ligands with preference for mu, delta, and kappa opiate receptor (morphine, Metenkephalin and ethylketocyclazocine) all have similar affinities toward beta h-endorphin sites in both brain and cerebellar membranes.

Animals↗
PubMed1983

Reversible neuromuscular blocking action of carboxymethylated alpha-bungarotoxin.

Carbamidomethylation of the reduced Cys29-Cys33 bridge of alpha-bungarotoxin (Bungarus multicinctus postsynaptic neurotoxin) did not alter the LD50 or irreversibility of the toxin, while carboxymethylated alpha-bungarotoxin was less potent and its neuromuscular blocking action in mouse diaphragm was reversible. The circular dichroic spectra of both modified toxins were similar but slightly different from that of native toxin. Neuromuscular transmission in the chick biventer cervicis nerve-muscle preparation could be blocked by the carboxymethylated toxin, and reactivated by washing, whereas the response of the muscle to extrinsic acetylcholine could also be blocked but was hardly restored by washing. These results suggest that carboxymethylated toxin can differentiate between junctional and extrajunctional acetylcholine receptors in chick skeletal muscle.

Amino Acid Sequence↗
PubMed1983

Mode of neuromuscular blocking action of ceruleotoxin.

Ceruleotoxin is an acidic toxin protein from a Bungarus venom which has recently been clarified as B. fasciatus venom. The toxin at a low concentration (10(-6) g/ml) abolished the twitch response of the indirectly stimulated biventer cervicis muscle of the chick, without affecting the response of acetylcholine or carbamylcholine. At a higher concentration (10(-5) g/ml), the toxin, in addition to inhibition of the twitch response, caused contracture in the chick biventer cervicis muscle and reduced the response to acetylcholine or carbamylcholine in both the innervated chick cervical and denervated rat diaphragm muscles. Electrophysiological studies on the rat phrenic nerve--diaphragm preparation showed that ceruleotoxin at a low concentration caused an initial inhibition followed by recovery of the quantal content of endplate potentials and then a second phase of inhibition leading to complete failure. At a higher concentration, the toxin gradually reduced the resting membrane potential of the diaphragm muscle to a level lower than 50 mV within 2 hr. In addition, enzyme assay showed that the toxin possessed phospholipase A activity comparable to that of other basic phospholipases A2 of snake venom origin. It is concluded that ceruleotoxin is a phospholipase A2 with presynaptic and myotropic actions on vertebrate nerve--muscle system similar to those of notexin from Notechis scutatus scutatus venom.

Action Potentials↗
PubMed1982

Site of action of caudoxin, a neurotoxic phospholipase A2 from the horned puff adder (Bitis caudalis) venom.

Caudoxin, a single-chain phospholipase A2 isolated from the venom of Bitis caudalis is a toxic polypeptide with a formula weight of 13,332 dalton. The LD50 in mice (i.p.) was 0.18 (0.15-0.22) mg/kg. In the chick biventer cervicis muscle preparation the toxin (1-10 micrograms per ml) caused complete neuromuscular blockade without affecting the response of the muscle to acetylcholine. In the mouse phrenic nerve-diaphragm preparation, the toxin abolished the indirectly elicited contraction without inhibiting that evoked directly. When this preparation was bathed in a low calcium (0.6 mM) medium, the toxin induced a triphasic change in the indirectly evoked contractions: an immediate initial inhibition followed by augmentation and then a second phase of inhibition leading to irreversible neuromuscular blockade. Electrophysiological studies in the same preparation showed a similar triphasic change in the quantal content of endplate potentials. The frequency of miniature endplate potentials first increased and then decreased, while the resting membrane potential was not significantly decreased by the toxin. Histological study showed that the toxin caused local myonecrosis only at a higher dose (2 mg/kg mouse). It is concluded that caudoxin produced a neuromuscular block by acting selectively on a presynaptic site. However, the site of binding appears to be different from that of beta-bungarotoxin since combination of the toxin with beta-bungarotoxin caused potentiation of its neuromuscular blocking action rather than addition.

Animals↗
PubMed1982

Purification and pharmacological characterization of a cardiotoxin-like protein from Formosan banded krait (Bungarus multicinctus) venom.

By ion exchange chromatography followed by gel filtration, a polypeptide toxin was purified from Formosan banded krait (Bungarus multicinctus) venom. The toxin had a molecular weight of 7000 +/- 300 and showed an amino acid composition characteristic of cardiotoxin from cobra venom. The i.p. LD50 value of the toxin was 2.5 (1.9-3.2) mg per kg mouse. Pharmacological studies showed that the toxin (10 micrograms/ml) induced contracture in chick and mouse skeletal muscles, depolarized the cell membrane of the mouse diaphragm, arrested the contraction of spontaneously beating atria and the electrically driven ventricle strip of the rat, and caused direct hemolysis of guinea-pig erythrocytes. From these chemical and pharmacological characterizations it was concluded that this toxin has characteristics similar to those of cobra venom cardiotoxins.

Amino Acids↗
PubMed1978

Synthesis of a fully active snake venom cardiotoxin by fragment condensation on solid polymer.

A polypeptide cardiotoxin containing 60 amino acids with 4 disulfide bonds has been synthesized by the "fragment solid-phase" method. The identity of the synthetic product with native cardiotoxin was established by chromatography on Sephadex G-50, carboxymethyl-cellulose column chromatography, thin layer chromatography, disc gel electrophoresis, amino acid analysis, end group analysis, peptide mapping, circular dichroism spectra, and four biological tests.

Amino Acid Sequence↗
PubMed1978

Purfication of synthetic cardiotoxin by affinity chromatography.

A polypeptide containing 60 amino acids with 4 disulphide bonds, synthesized by the solid-phase method, was highly purifed by anticardiotoxin-Sepharose affinity chromatography following gel filtration and CM-cellulose chromatography. The identification of the final product as cardiotoxin was confirmed by thin-layer chromatography on silica gel, polyacrylamide gel electrophoresis, amino acid analysis, circular dichroism spectra, N-terminal analysis and four biological tests.

Animals↗