Biomedical subjects

T C Chu

Publications and source records attributed to T C Chu.

At least 55 records · Page 3Linked to original sources

PubMed1993

Ocular hypotensive action of a dopaminergic (DA2) agonist, 2,10,11-trihydroxy-N-n-propylnoraporphine.

The dopamine (DA2) receptor agonist 2,10,11-trihydroxy-N-n-propylnoraporphine (TNPA) was tested for effects on 1) intraocular pressure (IOP), 2) aqueous humor flow rate, 3) electrically induced contractions of the cat nictitating membrane, 4) 3H-NE release from isolated rabbit iris-ciliary bodies and 5) cAMP accumulation in the isolated rabbit iris-ciliary body. Unilateral, topical administration of TNPA lowered IOP bilaterally in a dose-related fashion and inhibited the bilateral rise in IOP caused by water gavage. Topical pretreatment with metoclopramide, a DA antagonist, inhibited the ocular hypotensive response to TNPA. Subsequently, TNPA was shown to decrease aqueous humor inflow and IOP in normal rabbit eyes but not in surgically sympathectomized rabbit eyes. TNPA caused dose-dependent suppression of contractions of the cat nictitans, which was inhibited competitively by domperidone, a relatively selective DA2 receptor antagonist. In a test of prejunctional activity, TNPA caused dose-related inhibition of 3H-NE release from isolated, field-stimulated rabbit iris-ciliary bodies, which was inhibited by pretreatment with sulpiride, a relatively selective DA2 receptor antagonist. In a test of postjunctional activity, isoproterenol-stimulated cAMP accumulation in the isolated rabbit ciliary body was not affected by TNPA pretreatment. These results indicate that TNPA's suppressive action on aqueous humor flow rate and IOP is exerted predominantly on prejunctional (DA2) receptors of peripheral sympathetic nerves.

Animals↗

PubMed1993

Modification of catalytic properties of chicken liver fructose 1,6-bisphosphatase by allicin.

The activity of chicken liver fructose 1,6-bisphosphatase increases dramatically after incubation with allicin, a major biologically active compound produced by garlic. Activation is more pronounced when the enzyme is assayed with Mn2+ than Mg2+. Maximum activation is accompanied by the disappearance of 4 highly reactive sulfhydryl groups per molecule of enzyme. This modification also leads to loss of activation by K+, and reduced sensitivity to inhibition by AMP, fructose 2,6-bisphosphate, and high concentration of fructose 1,6-bisphosphate. All the altered properties induced by allicin can be reversed by dithiothreitol or tris(2-carboxyethyl)phosphine, the latter being much more effective.

Animals↗

PubMed1992

Intracellular pH regulation by a Na+/H+ exchanger in cultured bovine trabecular cells.

Intracellular pH (pHi) of cultured bovine trabecular cells was measured using video-imaging techniques with a pH-sensitive intracellular fluorescent dye, BCECF. In bicarbonate-rich Ringer at pH 7.4, pHi was 7.29 +/- 0.03 (+/- SEM, n = 12 monolayers, 120 cells sampled). Exposure to 20 mM NH4Cl immediately alkalinized pHi: replacement with a Na(+)-rich solution acidified pHi before recovery to resting levels. When NH4Cl was replaced by a low Na+ solution, acidification was sustained but pHi recovery occurred after Na(+)-rich solution. A pHi of 7.11 +/- 0.02 (n = 2 monolayers, 20 cells) occurred in pH 6.8 and pHi was 7.72 +/- 0.03 (n = 2 monolayers, 20 cells) in pH 8.0. Amiloride (1 mM) acidified pHi but DIDS (1 mM) treatment, HCO3(-)-free condition, 1 mM ouabain, 50 mM K+, and 2 mM BaCl2 failed to change pHi. Hydrogen peroxide (1 mM) acidified pHi but no change occurred with 50 microM. Trabecular cells possess an Na+/H+ exchanger similar to that in other cell types.

Ammonium Chloride↗

PubMed1992

Defective alloantigen-presenting capacity of 'Langerhans cell histiocytosis cells'.

The functional activity of skin cells derived from an infant who died of multisystem Langerhans cell histiocytosis (LCH) was examined. Involved and non-involved skin was obtained at postmortem examination within three hours of death; normal epidermal Langerhans cells and 'LCH cells' were separated by means of dispase digestion. The functional activity of different populations of CD1a positive cells was assessed using the conventional six day allogeneic mixed cell reaction. Compared with Langerhans cells from a healthy control, LCH cells showed minimal functional activity. However, Langerhans cells from non-involved skin showed normal and Langerhans cells overlying involved skin showed augmented functional activity. These findings suggest that LCH is a disease in which abnormal Langerhans cells accumulate and/or proliferate in various tissues but it does not affect the entire Langerhans cell population.

Antigens, CD↗

PubMed1992

Comparative studies of furosemide effects on membrane potential and intracellular chloride activity in human and rabbit ciliary epithelium.

Furosemide (1 mM), a potent loop diuretic, caused a 10-mV (n = 14) depolarization of the intracellular potential difference (PDI) of isolated rabbit ciliary epithelium (CE), but produced a 9-mV (n = 5) hyperpolarization of PDI of isolated human CE. In rabbit CE, furosemide consistently depolarized PDI by 13, 7 and 8 mV in HCO3(-)-free Ringer, Na(+)-free Ringer and after BaCl2 treatment, respectively. The depolarization of PDI was reduced to 2 mV (n = 11) in Cl(-)-free conditions. A hyperpolarization of PDI caused by furosemide that was quantitatively similar to that seen in normal Ringer also occurred in human CE during immersion in HCO3(-)-free Ringer, Na(+)-free Ringer and after BaCl2 treatment. There was a small hyperpolarization (3 mV) of PDI in Cl(-)-free conditions. Human or rabbit tissue-cultured nonpigmented ciliary epithelial cells were loaded with the Cl(-)-sensitive fluorophore 6-methoxy-N-(3-sulfopropyl) quinolinium (SPQ) in hypotonic solution (145 mosm) for 4 min at 37 degrees C. Furosemide decreased intracellular Cl- fluorescence activity of both human and rabbit ciliary epithelial cells by 30 +/- 5 (n = 8) and 25 +/- 7% (n = 13), respectively, when the cells were immersed in Cl(-)-rich solution. It is suggested that a furosemide-sensitive Cl- movement exists in both rabbit and human CE, although the mode of Cl- movement to the aqueous across CE may differ between these species.

Animals↗

PubMed1992

Intracellular pH of tissue-cultured bovine corneal endothelial cells.

Intracellular pH (pHi) of bovine tissue-cultured corneal endothelial cells has been measured under several experimental conditions. Determinations were made on individual cells using video-imaging techniques that allowed assessment of 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein fluorescence at 440 and 490 nm. Each experiment had a calibration performed on a cell monolayer: this was performed using a high K(+)-nigericin solution. Resting pHi was 7.25 +/- 0.03 (n = 18) in bicarbonate solution at pH 7.4. Amiloride (1 mM) caused an acidification of approximately 0.2 U within 2 min: replacement with normal Ringer allowed a return to normal pHi after an alkali overshoot. Exposure to 20 mM NH4Cl caused alkalinization that became acidic upon washout of NH4Cl. In Na(+)-rich solution pHi returned to normal after acidification but pHi remained low in Na(+)-free solution until substituted by Na(+)-rich solution. Removal of HCO3- from the bathing solution caused a nonsignificant acidification of pHi by 0.1 U at 2 and 4 min, and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 1 mM) acidified pHi by 0.14 U at 2 min and 0.24 U at 4 min. Addition of DIDS (1 mM) in a HCO3(-)-free solution had no effect on pHi. Hydrogen peroxide acidified pHi by 0.3 U at 50 microM and 1 mM. These results indicate that a Na+:H+ antiport exists that regulates pHi even at normal ambient pH in the presence of bicarbonate: this process becomes highly activated after an acid load. There is a DIDS-sensitive HCO3- movement that is probably coupled to Na+ or Cl-.

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

PubMed1992

Radon concentration in two largest cities in semitropical Taiwan.

Grab sampling either using the active charcoal method in combination with an ionization chamber or using a working level monitor was performed for the measurement of radon concentration in Taiwan's two largest cities Taipei and Kaohsiung. Long-term monitoring of radon concentration in dwellings and business buildings was also carried out with cellulose nitrate films as the alpha detectors. The average indoor radon concentration in these two cities is 17 +/- 6 Bq m-3. The outdoor radon concentration is about one-half of that on average. As assessed according to the model of UNSCEAR 1988, the induced effective dose equivalent is 0.67 mSv y-1. Radon concentration in coal mines showed an average of 88.5 +/- 9.5 Bq m-3.

Air Pollutants, Radioactive↗

PubMed1992

Concentrations of radionuclides of size fractionated fly-ash emissions from a thermal power plant using Taiwan coal.

Coal, fly ash and bottom ash samples were taken from a 300-MWe coal-fired power plant with a daily coal consumption of 2400 tons. A high volume sampler coupled with several mesh testing sieves was used to separate fly ash samples into different size fractions. Determination of the concentrations of 40K, 238U, 226Ra, 210Pb, 210Po, 228Th and 228Ra was carried out either by gamma or alpha spectrometry. For elements volatilized during combustion, their radionuclide concentrations decrease with increasing particle size. The enrichment factors for all radionuclides mentioned above were studied. Their values range from 31.0 for 210Po to 2.2 for 228Ra. Of all radionuclides studied, 210Po and 210Pb are the most volatile elements; therefore, an increase in the natural radiation level should first be indicated by an increase in these two nuclides.

Air Pollutants, Radioactive↗

PubMed1991

Natural radiation background in metropolitan Taipei.

A high-pressure ionization chamber was used to measure the natural background radiation in metropolitan Taipei, Taiwan, R.O.C. during a period in 1987-1988. The average exposure rate was 27.55 x 10(-10) C kg-1 h-1 including cosmic radiation, but the radon contribution was excluded. Scintillation survey meter, gamma-ray spectroscopy for soil samples, in-situ measurement with a NaI(Tl) detector coupled to a portable multichannel analyzer, instrumental neutron activation analysis of rock samples, and even thermoluminescent dosimeters were used as complementary measuring devices. Areas of higher radiation background were detected. They are the radium-bearing Peitou stones, an unusual occurrence of uraniferous zone at Sanhsia, and uranium precipitation in the glassy olivine basalt in a tea field at Tachi. All these areas are located in suburban sites of Taipei. Three types of building in Taipei City were selected for radon detection. No significantly elevated level of radon was detected, since Taipei is located in a semitropical area where ventilation of buildings is not a problem.

Background Radiation↗

PubMed1991

Ascorbate-stimulated active Na+ transport in rabbit ciliary epithelium.

In a physiological medium (134 mM Na+ concentration), unidirectional blood-to-aqueous and aqueous-to-blood Na+ fluxes across the isolated rabbit ciliary epithelium are large, rendering the detection of a net transport difficult. At 134 mM an active component for Na+ may be obscured by diffusional fluxes and a bidirectional Na(+)-Cl- cotransport. Considering that the active transport saturates at about 30 mM, experiments were performed at this reduced Na+ concentration to minimize the influence of diffusional pathways. A net blood-to-aqueous Na+ flux that ranged from 0.25 to 0.81 mu eq/hr was obtained. Addition of ascorbic acid to the aqueous side under this condition increased the blood-to-aqueous flux with little effect on the flux in the opposite direction. Ouabain inhibited both the Na+ and ascorbate-stimulated Na+ transport. The increase in blood-to-aqueous Na+ flux by ascorbate was also observed in tissues bathed with [Na+] closer to physiological levels (100 mM). These results indicate that the rabbit ciliary epithelium transports Na+ into the posterior chamber. Since aqueous ascorbate stimulates Na+ transport, it may be implicated in both Na+ movement and aqueous humor secretion. However, the rate of Na+ transport can only account for a small fraction of total aqueous humor production.

Animals↗

PubMed1990

Direct stimulation by succinate of Na+:K+ pump in rabbit ciliary epithelium.

The effects of succinate on the intracellular potential difference, PDI, were measured in isolated rabbit ciliary processes. Concentration-dependent increases in the hyperpolarization of PDI occurred between 1 and 15 mM succinate in NaCl Ringers. With 5 mM succinate, there was a 6 mV hyperpolarization. Even though the hyperpolarization of PDI was comparable with 10 and 15 mM succinate, it was more sustained at the latter two concentrations. Succinate also elicited comparable hyperpolarizations of PDI in either Cl(-)-free or HCO3(-)-free Ringers. Similarly, following incubation with either 0.1 mM DIDS or 3 mM BaCl2 the effect of succinate on PDI was unchanged. Five mM succinate had no effect if it was added after 5 mM malonate. Malonate (5 mM) rapidly reversed a 5 mM succinate-induced hyperpolarization of PDI which also suggests a metabolically mediated effect on PDI. An isosmotic substitution of Na+ with NMDG Ringers depolarized PDI, whereas PDI depolarized biphasically during exposure to 0.1 mM ouabain. The addition of 5 mM succinate had no effect on either the time course or the magnitude of the depolarization of PDI during blocking of the Na+:K+ pump with either Na(+)-free Ringers or ouabain. Taken together, these results show that succinate selectively stimulates the Na+:K+ pump, but has no effect on any Cl-, HCO3- or a Ba2(+)-sensitive K+ conductance.

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

PubMed1990

Effects of adrenergic drugs on intracellular electrical potential difference of rabbit ciliary epithelial cells.

The effects of adrenergic drugs on intracellular electrical potential difference (PDI) of rabbit ciliary epithelial cells were investigated. Epinephrine as well as norepinephrine hyperpolarized the PDI at lower concentrations (10(-6) M) and depolarized the PDI at higher concentrations (greater than 10(-5) M). Isoproterenol produced a depolarization of PDI and phenylephrine caused a hyperpolarization only. After pretreatment with propranolol, the change of PDI by isoproterenol was minimal. Selective agonists and antagonists were used to further characterize adrenergic effects on the PDI. Both beta 1 and beta 2 agonists caused a depolarization of PDI while both beta 1 and beta 2 antagonists produced a hyperpolarization. Alpha 1 antagonist depolarized the PDI and alpha 2 antagonist hyperpolarized the PDI. Such electrophysiological effects of the adrenergic drugs confirm the presence of alpha and beta adrenoceptors in the rabbit ciliary epithelial cells.

Adrenergic alpha-Agonists↗

PubMed1990

Bicarbonate and DIDS effects on intracellular potential difference in rabbit ciliary epithelium.

A change of [HCO3-] in the solution bathing isolated rabbit ciliary epithelium from 30 mM to 0, or vice versa, resulted in a change of intracellular electrical potential difference (PDI) of 7 mV. Intermediate [HCO3-] (5, 10 and 15 mM) solutions were also tested. No perceivable change of PDI occurred when [HCO3-] changed from 30 to 15 mM. PDI depolarized gradually when [HCO3-] decreased from 30 or 15 mM to 0 mM, but PDI hyperpolarized at a faster rate when [HCO3-] increased from 0 to 15 or 30 mM. The amount of change of PDI from 15 to 5 mM, or vice versa, and from 10 to 0 mM or vice versa, was 4 mV. The stilbene, DIDS (10(-4) M), hyperpolarized the PDI in HCO3(-)-rich solutions. The response of DIDS was reduced in HCO3(-)-free medium and inhibited in Cl(-)-free solution. The results suggest the existence of an electrogenic bicarbonate transport or Na+/HCO3- cotransport system.

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

PubMed1989

Changes in per capita and collective dose equivalent due to natural radiation in Taiwan (1950-1983).

This paper deals with the changes in per capita and collective dose equivalent in Taiwan in the past three decades based on the measured terrestrial and cosmic radiation levels and the population distribution as well. Over 70% of the population is concentrated in three population centers which have been naturally formed in the north, middle and south of Taiwan along the west coast as a result of industrialization and population growth. The population has increased 2.5 times in the past 33 y and reached to 1.9 X 10(7) persons, yet the migration of population was from the rural areas where the natural radiation is usually high to the urban areas where the natural radiation is usually low. The resulting collective dose equivalent has been increasing, yet the per capita dose equivalent, on the contrary, has been decreasing.

Background Radiation↗

PubMed1989

Prostaglandins and transepithelial ionic transport.

Given the complexity of the preparation and the fact that the measured potential difference and SCC result from the algebraic contribution of several apparent ionic components (as well as unidentified ones) in the various cell membranes of the preparation, the effect of PGF2 alpha on the SCC requires further elucidation, for example, by determination of the effects of this PG on H14CO3- fluxes. However, experiments already completed suggest that PGF2 alpha can effectively stimulate the SCC of the ciliary epithelium. Since stimulation of the SCC can be expected to reflect enhanced fluid secretion, the effect of PGF2 alpha on the ciliary epithelium, at least in rabbits, can be regarded as a potentially beneficial one, providing increased production of aqueous humor. It remains to be seen whether PGF2 alpha has a similar stimulatory effect on ciliary epithelium transport function in primates whose aqueous humor, in contrast to rabbits, is deficient in HCO3- as compared to blood plasma. The possibility that PGF2 alpha does stimulate aqueous humor secretion in the human eye is suggested by the fact that PGF2 alpha-1-isopropylester applied topically to the human eye in doses greater than the minimal dose required to cause ocular hypotension yields an initial increase in intraocular pressure (see Alm and Villumsen, 1989) and a small increase in rate of aqueous production was detected in the PGF2 alpha treated eyes of cynomolgus monkeys (Nilsson et al., 1989). These considerations suggest that the effects of PGs on the transport function of the mammalian ciliary epithelium deserves further attention.

Animals↗

PubMed1988

Role of alpha 1- and alpha 2-adrenergic receptors in Cl- transport across frog corneal epithelium.

Norepinephrine, 10(-6) M, reduced Cl- transport by 26% in 75% of isolated frog corneal epithelia. This inhibition was not previously reported. Since beta-adrenergic agonists are known to only stimulate Cl- transport, the action of specific alpha 1- and alpha 2-agonists on Cl- transport and electrical parameters was investigated. Phenylephrine, an alpha 1-agonist always stimulated the Cl(-)-dependent short-circuit current (Isc), but less than the beta-agonists. UK-14,304-18 (UK), a selective alpha 2-agonist, reduced both the Isc (by 31% at 10(-5) M) and the stroma-to-tear unidirectional Cl- flux. UK hyperpolarized the apical membrane potential difference and increased the transepithelial resistance and apical-to-basolateral resistance ratio. UK reduced forskolin-stimulated adenylate cyclase activity by 36%. The electrophysiological effects of UK are consistent with a reduction of the Cl- permeability at the apical membrane. Pretreatment with UK sensitized the tissue for a greater effect by forskolin. Results show that the frog corneal epithelium also possesses alpha 1- and alpha 2-receptors, the latter negatively coupled to the adenylate cyclase system. Cl- transport is thus regulated by an interaction between the positive effects of beta- and alpha 1-stimulation and the negative influence of alpha 2-stimulation.

Adenylyl Cyclases↗

PubMed1988

Active transport of ascorbate across the isolated rabbit ciliary epithelium.

The transepithelial transport of ascorbate across the isolated rabbit ciliary epithelium (CE) was investigated. Unidirectional 14C-ascorbate fluxes were measured in the presence of equal concentrations of ascorbate on both sides of the tissue within the range of 0.025 to 1 mM. The blood to aqueous (Bl----Aq) flux increased from 6 to 95 nmoles/hr and showed nonlinearity and saturation. The aqueous to blood (Aq----Bl) flux increased, for the same range, from 0.5 to 23 nmoles/hr in a linear fashion. The permeability calculated from the Aq----Bl flux was similar to the CE permeability for mannitol suggesting that the Aq----Bl flux is mainly paracellular. The flux ratio Bl----Aq/Aq----Bl was between 4 to 12. Anoxia, ouabain and low Na+ in the media inhibited the Bl----Aq flux indicating that the transport system requires energy and a Na+ gradient. 3-O-methyl-D-glucose, D-isoascorbic acid and phlorizin also inhibited the Bl----Aq flux, suggesting that ascorbate and glucose may share a common carrier mechanism. Although the isolated CE preparation was clearly capable of flux separation and active transport, the rate of ascorbate transport measured in vitro is insufficient to maintain the aqueous ascorbate concentration observed in vivo.

3-O-Methylglucose↗

PubMed1987

Electrically silent Na+ and Cl- fluxes across the rabbit ciliary epithelium.

Unidirectional Na+, Cl-, and mannitol fluxes were measured across the isolated and short-circuited rabbit iris-ciliary body as functions of the Cl- concentration in the bathing solution (0, 26 and 80 mM). At constant Na+ concentration, Na+ fluxes increased on the average from 8.0 to 11.9 mu eq/hr as the Cl- concentration was raised and vice versa. Cl- fluxes also increased more than expected from simple diffusion; from 2.0 (26 mM) to 8.1 mu eq/hr (80 mM). Mannitol permeability (9.0 X 10(-7) cm/sec) was independent of the Cl- concentration and similar to that measured in "tight" epithelia. In Cl(-)-free solutions, there was good agreement between the measured electrical resistance and that calculated with the partial conductance equation. In Cl(-)-rich solutions, the calculated resistance was smaller than the measured resistance, suggesting electrically silent fluxes of Na+ and Cl-. These silent fluxes were of similar magnitude and possibly coupled with each other. This mechanism may provide an additional pathway for electrolyte movement across the ciliary epithelium.

Animals↗