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W H Ko

Publications and source records attributed to W H Ko.

At least 55 records · Page 3Linked to original sources
PubMed1995

Sr2+ can become incorporated into an agonist-sensitive, cytoplasmic Ca2+ store in a cell line derived from the equine sweat gland epithelium.

We have explored the properties of a Ca(2+)-dependent cell-signalling pathway that becomes active when cultured equine sweat gland cells are stimulated with ATP. The ATP-regulated, Ca(2+)-influx pathway allowed Sr2+ to enter the cytoplasm but permitted only a minimal influx of Ba2+. Experiments in which cells were repeatedly stimulated with ATP suggested that Sr2+, but not Ba2+, could become incorporated into the agonist-sensitive, cytoplasmic Ca2+ store. Further evidence for this was provided by experiments using ionomycin, a Ca2+ ionophore which has no affinity for Sr2+.

Adenosine Triphosphate↗
PubMed1995

Different regulatory pathways involved in ATP-stimulated chloride secretion in rat epididymal epithelium.

The regulatory pathways involved in the ATP-stimulated Cl- secretion across rat epididymal epithelium were investigated by the short-circuit current (ISC) technique. Biphasic characteristic was observed in the ISC responded to ATP (0.01-10 microM). Inhibitor of P1 receptor, 8-phenyltheophylline (up to 100 microM), did not have any effect on both phases of the ATP-stimulated ISC. The order of potency for stimulation of the two phases in ISC was ATP > ADP >> AMP, adenosine, consistent with the presence of P2-purinoceptors. Cl- channel blocker, disulfonic acid stilbene (DIDS, 300 microM), only inhibited the first peak of the ATP-stimulated ISC while diphenylamine-dicarboxylic acid (DPC, 1 mM) reduced both, indicating the involvement of different conductance pathways. DIDS was found to have an inhibitory effect on Ca(2+)-activated ISC (induced by ionomycin, 10 microM) but not cAMP-activated ISC (induced by forskolin, 1 microM) which could only be blocked by DPC. Both peaks of the ATP-activated ISC could be significantly inhibited by pretreatment with a Ca(2+)-chelating agent, BAPTA-AM (50 microM). An increase in cellular cAMP content upon stimulation of ATP was measured by radioimmunoassay. No significant increase in cAMP production was observed in cells stimulated with adenosine. The ATP-induced cAMP increase was prevented by pretreatment with BAPTA-AM (100 microM) indicating that cAMP production upon ATP stimulation was secondary to an increase in intracellular Ca2+ concentration. These results indicate that the ATP-stimulated Cl- secretion could be mediated by Ca2+ and cAMP-dependent regulatory pathways giving rise to the biphasic nature of the ATP-induced ISC.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1995

Calcium-dependent regulation of membrane ion permeability in a cell line derived from the equine sweat gland epithelium.

We measured the rates of 125I- and 86Rb+ efflux from preloaded, cultured equine sweat gland cells. The calcium ionophore ionomycin increased the efflux of both isotopes. Anion efflux was unaffected by Ba2+, but this cation inhibited 86Rb(+)-efflux, suggesting that [Ca2+]i-activated potassium channels were present. Activation of these channels was not, however, important for the efflux of anions. We measured 125I- efflux from valinomycin-depolarised cells in which anion cotransport was inhibited. Changes in 125I- efflux reflect changes in anion permeability under these conditions, and ionomycin caused a clear permeability increase that was abolished by the anion channel blocker diphenylamine-2-carboxylate. ATP and UTP increased the efflux of both isotopes, suggesting that type P2U purine receptors allow these nucleotides to regulate membrane permeability.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1995

Contactless semi-implantable electromagnetic middle ear device for the treatment of sensorineural hearing loss. Short-term and long-term animal experiments.

A contactless electromagnetic hearing device has been designed following basic science experiments, improvement of electronics, and precision micromechanics. Different prototypes have been developed and tested in the laboratory, fresh human temporal bones, and acute and chronic animal experimentation. A conductive hearing loss model was first developed in the cat using samarium cobalt as the target magnet. Later, a highly efficient electromagnetic air-core coil was selected to vibrate a neodymium iron boron magnet cemented to the body of the incus and tested in acute and chronic experiments using the cat as the model. In this group of animals, the ossicular chain was left intact. There was no failure of the target magnet, driving coil, or implanted electronics. The only problem encountered in this evaluation was a malfunction of the receiving antenna that had to be redesigned and retrofitted into the implanted units. This system would be suitable for the treatment of moderate to severe sensorineural hearing loss. Planning to begin human clinical trials is ongoing.

Animals↗
PubMed1995

Engineering principles of mechanical stimulation of the middle ear.

This article presents the transducer principles of possible middle ear hearing devices with their characteristics and selection considerations summarized. The frequency response and the needed force and displacement at the ossicular chain sites were measured to determine approximately the system requirements and design considerations. The power required to vibrate the ossicular chain is estimated to be of the order of 0.1 watt, which is three orders of magnitude smaller than the power consumption of devices being developed in various laboratories. Careful engineering design and evaluation is needed. A design example of the transducer used with a partially implantable, noncontact electromagnetic hearing device is presented in this article with laboratory evaluation results.

Biomedical Engineering↗
PubMed1994

The regulation of membrane 125I- and 86Rb+ permeability in a virally transformed cell line (NCL-SG3) derived from the human sweat gland epithelium.

We have explored the factors that may regulate membrane permeability in a cell line (NCL-SG3) derived from the human sweat gland epithelium. Ionomycin increased the rate of 125I-efflux from preloaded cells and this action appeared to be due to an increase in intracellular free calcium ([Ca2+]i). The ionomycin-evoked increase in 125I- efflux was reduced in cells that were exposed either to barium or to valinomycin in the presence of a high concentration of external potassium. It thus appears that a fraction of the ionomycin-evoked increase in 125I- efflux is due to the activation of potassium channels and experiments using 86Rb+ also suggested that ionomycin increased the rate of potassium efflux, an effect which was totally abolished by barium. Blockade of Na(+)-K(+)-2Cl- cotransport and of Cl- -HCO3- exchange reduced the basal rate of 125I- efflux and the ionomycin-evoked increase in 125I-efflux from control cells and from cells depolarized by valinomycin. These transport systems thus contribute to anion efflux, although [Ca2+]i-dependent chloride channels also appear to be present. Acetylcholine increases [Ca2+]i in the secretory cells of human sweat glands, but this neurotransmitter did not increase [Ca2+]i in NCL-SG3 cells and so membrane permeability was not under cholinergic control. Adrenaline did not increase [Ca2+]i, but this hormone did evoke cyclic-3',5'-adenosine monophosphate (cyclic AMP) production. However, membrane permeability was not under adrenergic control, as the cells did not appear to express functional, cyclic AMP-dependent anion channels. This may be because they were not fully differentiated under the culture conditions. ATP consistently evoked a dose-dependent increase in anion efflux that appeared to be mediated by [Ca2+]i. The increase in [Ca2+]i was initiated by the release of calcium from a limited internal store and was subsequently sustained by calcium influx. UTP and ADP also increased [Ca2+]i, whereas adenosine, AMP and alpha,beta-methylene ATP were without effect. These data thus suggest that a subclass of type 2 purine receptor, which is functionally coupled to phosphoinositidase C, is present in these cells.

Calcium↗
PubMed1994

The effect of [Arg8]vasopressin on electrogenic chloride secretion in cultured rat epididymal epithelia.

Primary cultured rat efferent ductal epithelia and cauda epididymal epithelial were mounted in Ussing chambers to study the effect of arginine vasopressin (AVP) on chloride secretion in the male excurrent duct. The regional differences in the signal transduction pathways involved were also investigated. In both the efferent duct and the cauda epididymidis, basolateral addition of AVP resulted in a dose-dependent increase in the short-circuit current (Isc), which was mediated via V1 receptor. Replacement of ambient Cl- with gluconate or pretreatment of a Cl- channel blocker, diphenylamine-2-carboxylate (apical, 1 mM), completely abolished the response, whereas addition of amiloride had no effect on the Isc. Pretreating the epithelia of the efferent duct with indomethacin (apical, 5 microM) or forskolin (basolateral, 1 microM), but not thapsigargin (apical, 1 microM) or trifluoperazine (apical, 20 microM), significantly inhibited the AVP response (P < 0.001). By comparison, pretreating the epithelia of the cauda epididymidis with any of the four agents significantly reduced the AVP-evoked response. These results suggested that the stimulation of chloride secretion by AVP in the efferent duct and the cauda epididymidis is mediated by prostaglandin synthesis and involves adenosine 3',5'-cyclic monophosphate (cAMP) as a second messenger. In the cauda epididymidis, calcium, in addition to cAMP, may play a role in mediating the AVP-induced response.

Animals↗
PubMed1994

Extracellular ATP can activate autonomic signal transduction pathways in cultured equine sweat gland epithelial cells.

Changes in intracellular free calcium concentration ([Ca2+]i) were monitored in a cell line that was derived from the equine sweat gland epithelium. ATP and closely related compounds could increase [Ca2+]i with a rank order of potency of UTP > or = ATP > ADP >> AMP = adenosine = alpha,beta-methylene-ATP. The responses to ATP and to UTP were initiated by the release of calcium from an internal store and subsequently sustained by calcium influx. The rise in [Ca2+]i thus seems to be mediated by P2U receptors that are coupled to phosphoinositidase C. Some desensitisation of this response developed during repeated stimulation with ATP and this was blocked by staurosporine, an inhibitor of protein kinase C, and augmented by a phorbol ester which acts as an exogenous activator of this enzyme. A protein-kinase-C-dependent inhibitory pathway thus seems to become active during repeated stimulation with ATP. ATP and related compounds could also raise cellular cyclic AMP content. The order of potency was ATP > ADP = AMP = adenosine >> UTP, suggesting that this response is mediated via a separate subclass of P2 receptor. The present results demonstrate that ATP can activate autonomic signal-transduction pathways in cultured equine sweat gland cells and suggest that there may be a purinergic component to the control of secretory activity in the equine sweat gland.

Adenosine Triphosphate↗
PubMed1994

Renal reabsorption of trichosanthin and the effect on GFR.

Trichosanthin (TCS) is a ribosome-inactivating protein that has a wide range of biological and pharmacological activities. Due to its small molecular size, TCS is filtered by the glomerulus and can be recovered from urine. A previous experiment showed that the kidney is an important organ for its elimination. However, urine TCS recovery was unexpectedly small, suggesting renal reabsorption of this compound. To substantiate renal TCS reabsorption, different doses of TCS were injected intravenously into rats. Increasing the dose from 0.375 mg/kg to 12 mg/kg enhanced the percentage urine recovery from less than 0.29 +/- 0.06% to 39.07 +/- 2.46%. This demonstrated that TCS is reabsorbed by a saturable mechanism. Reabsorption of most small molecular weight filterable proteins shares a common endocytotic process. It is very likely that TCS utilizes the same process for reabsorption. When a filterable protein such as hemoglobin was infused with TCS, it competed with TCS for reabsorption and therefore increased the percentage urine TCS recovery to 35 +/- 2%. Infusion of another filterable protein, lysozyme, increased recovery to 3.2 +/- 0.8%. This supports the proposal that renal TCS uptake utilizes the common endocytotic mechanism. It was also found in this study that injection of TCS depressed the glomerular filtration rate (GFR), implying renal toxicity. This effect can be attributed to ribosome inactivation which takes place inside the cells. Should reabsorption of TCS be reduced, renal toxicity will disappear. For this purpose, dextran-trichosanthin (DXTCS) conjugate was synthesized to increase its effective molecular size.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

A contactless electromagnetic implantable middle ear device for sensorineural hearing loss.

Following basic science experiments, improvement of precision micromechanics and electronics design, and development of different prototypes, a contactless electromagnetic hearing device has been successfully implanted in cats (acute experiments). Chronic animal experiments using the cat as well as the rabbit are ongoing to test the components of the device. A highly efficient air core coil is used to vibrate a neodymium-iron-boron magnet cemented to the body of the incus. The parts of the system, including implanted electronics (hybrid circuit, solid state), are laser welded and hermetically sealed. The system allows for the generation of enough force which vibrates the magnet implanted on the incus. It would be suitable for the treatment of moderate to severe sensorineural hearing loss.

Animals↗
PubMed1993

The biological activities of trichosanthin after coupling to dextran.

1. The major biological and pharmacological activities of trichosanthin (TCS) were retained after its covalent coupling to dextran T40. The potency and toxicity was generally reduced. 2. A dose of TCS as low as 0.02 mg/25 g induced 100% mid-term abortion whereas 20 times as much dextran-trichosanthin (DX-TCS) is required to produce the same effect. 3. A third of the mice died at a TCS dose of 0.1 mg/25 g but 4 times as much DX-TCS did not cause any death. 4. DX-TCS suppressed Con A or PHA induced lymphocyte transformation in a dose dependent manner. The potency was decreased as compared to TCS. 5. Both TCS and DX-TCS exhibited a cytostatic effect on cultured tumour cells (PU5 and hepatoma), the former being more potent.

Abortifacient Agents↗
PubMed1993

Two widely accessible media for growth and reproduction of phytophthora and pythium species.

Tomato agar and soybean agar were found to be comparable to or in some cases better than the popular V8 vegetable juice agar in supporting linear growth of Phytophthora cactorum, Phytophthora capsici, Phytophthora parasitica, Pythium aphanidermatum, and Pythium splendens; sporangium production of P. capsici, P. palmivora, and Pythium splendens; and oospore formation of P. cactorum, P. parasitica, Pythium aphanidermatum and Pythium splendens. These two media with readily accessible ingredients can be used to substitute for V8 juice agar in pathological and physiological studies of these two important groups of fungi in countries where V8 vegetable juice is not available or difficult to obtain.

Journal Article↗
PubMed1993

Investigation of stimulus-secretion coupling in equine sweat gland epithelia using cell culture techniques.

When sweat glands isolated from samples of horse skin were explanted and cultured under favourable conditions, they could exhibit cellular outgrowth. This growth could be maintained for 2-4 weeks and these primary cultures were then disaggregated and the resultant cell suspensions used to initiate epithelial cell lines. Secretion from intact equine sweat glands is regulated by beta 2-adrenoceptors and appears to be mediated by cyclic AMP, but there is evidence that calcium may also play a role. Adrenaline could increase the cyclic AMP content of the cultured cells and this response was mediated by beta 2-adrenoceptors. Adrenaline was also able to evoke a small increase in intracellular free calcium ([Ca2+]i) but the pharmacology of this response remains obscure. Adrenaline thus activates at least two potentially important second-messenger signalling pathways which have the capacity to interact, because adrenaline-evoked cyclic AMP formation was inhibited if [Ca2+]i was raised with ionomycin. The chloride permeability of mammalian epithelial cells characteristically rises during secretion, and adrenaline could increase chloride permeability in the cultured epithelia but the cells did not contain cyclic-AMP-dependent chloride channels and so this response was mediated by [Ca2+]i.

Animals↗
PubMed1992

Modulation of trichosanthin antigenicity by coupling to dextran.

Trichosanthin (TCS) is a plant-derived type I ribosome-inactivating protein with a wide spectrum of biological and pharmacological activities. Recently, it was covalently coupled to dextran in order to prolong its half-life in plasma. The major biological activities were generally retained but at lower potency. The immunogenicity of the dextran-trichosanthin (DX-TCS) was compared to that of TCS itself in this study. The results showed that mice immunized with TCS produced 8 times as much TCS-reactive IgE than those immunized with DX-TCS. However, both TCS and DX-TCS immunization produced similar titers of TCS-reactive IgG. A trace of dextran-reactive IgG was detected in mice immunized with DX-TCS. Thus, coupling of TCS to dextran reduced its antigenicity but slightly enhanced that of dextran, and the conjugate elicited less IgE than TCS.

Adjuvants, Immunologic↗
PubMed1992

Effect of lysine on hemolysis-induced kidney damage.

The mechanism of kidney damage commonly seen in patients with intravascular hemolysis is not entirely clear. Injection of distilled water (4 ml within 5 seconds) into the carotid arteries of rats resulted in intravascular hemolysis leading to hemoglobinemia, hemoglobinuria, reduction in inulin clearance, and elevation of urine N-acetyl-beta-D-glucosaminidase (NAG) excretion. When the same experiment was repeated with simultaneous infusion of the positively charged amino acid lysine (30 mmol/L at 3.4 ml/hour), the inulin clearance was unchanged. Urinary NAG excretion was elevated but significantly lower than that in similar rats without lysine infusion. This suggested that lysine protected the kidney from the deleterious effect of hemolysis. Such protection was not observed when the neutral amino acid glycine was infused. Because positively charged but not neutral amino acids are known to inhibit renal protein reabsorption, the protective effect of lysine could be due to inhibition of hemoglobin reabsorption, which might be an important step in the pathogenesis of kidney damage.

Acetylglucosaminidase↗
PubMed1991

Increasing the plasma half-life of trichosanthin by coupling to dextran.

Trichosanthin (TCS) is a plant protein which has a wide spectrum of pharmacological activities. It was demonstrated recently that this compound suppressed the replication of human immunodeficiency virus (HIV-1) in vitro. The mechanism of action is believed to be inhibition of protein synthesis. Trichosanthin is a low molecular weight protein which is expected to be easily filtered and eliminated through the kidney. To minimize renal loss, the molecular size of trichosanthin can be increased by coupling to dextran. The larger complex will not undergo glomerular filtration and therefore renal loss can be prevented. This study investigates the kidney's role in trichosanthin elimination and the beneficial effect afforded by coupling to dextran in prolonging plasma half-life. For this purpose, a radioimmunoassay has been developed to determine the concentration of TCS in plasma and urine. The sensitivity of this assay is in the nanogram range. Trichosanthin was coupled to dextran T40 by a dialdehyde method and successful coupling was confirmed by gel filtration chromatography. The complex retained specific binding to trichosanthin antibodies with decreased affinity which can be partially reversed after incubation with dextranase; an enzyme that digested dextran. The pharmacokinetics of intravenously administered trichosanthin (0.75 mg/kg) was compared between two groups of rats with normal and impaired renal function (bilateral renal arterial ligation). Rats with ligation showed a decrease in plasma clearance from 4780 +/- 570 to 220 +/- 20 microL/min and an increase in the mean residence time from 9 +/- 1 to 145 +/- 16 min. Despite the several-fold difference in these parameters, recovery of trichosanthin from normal rat urine was only 0.38 +/- 0.05%. This value can be increased by using higher injection doses. The data indicate that the kidney is an important organ for the elimination of trichosanthin. When the dextran-trichosanthin complex was injected into normal rats trichosanthin activity was not detected in the urine. All the pharmacokinetic parameters suggest that the dextran-trichosanthin complex stayed longer in the body and maintained a much higher plasma concentration than trichosanthin.

Animals↗
PubMed1988

Ventricular volume regulation: a mathematical model and computer simulation.

A mathematical model of ventricular volume regulation based on fluid mechanical principles has been constructed using a systems engineering approach. The parameters used in the model are based on clinical observation, laboratory investigation, and presumptions that will be tested later. The model was constructed to be the basis of a computer simulation. Using the computer simulation, information obtained from the literature and laboratory hypotheses regarding pathophysiology, several enigmatic conditions were tested. The model predicted that over-production of cerebrospinal fluid, as in the case of choroid plexus papilloma, could by itself lead to distention of the ventricular system. In simulating pseudotumor cerebri, if cerebrospinal fluid absorption at the arachnoid villi is impaired and the brain itself is rendered incompressible by swelling, intracranial pressure rises and ventricular volume diminishes. Conversely, in normal-pressure hydrocephalus, if cerebrospinal fluid flow is restricted between the spinal and cortical subarachnoid spaces and the brain is made more compressible, the ventricular volume increases with minimal increases in intracranial pressure. This mathematical model and its associated computer simulation is useful in predicting the behavior of the volume of the cerebral ventricles to a variety of pathological phenomena.

Animals↗