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Biomedical subjects

C O Lee

Publications and source records attributed to C O Lee.

At least 73 records · Page 4Linked to original sources
PubMed1996

New bioactive cerebrosides from Arisaema amurense.

From Arisaema amurense, four new cerebrosides were isolated along with a known cerebroside. The new cerebrosides were characterized as 1-O-beta-D-glucopyranosyl- (2S,3R,4E,8Z)-2-[(2(R)- hydroxyicosanoyl)amido]-4,8-octadecadiene-1,3-diol (1), 1-O-beta-D- glucopyranosyl-(2S,3R,4E,8Z)- 2-[(2-hydroxyoctadecanoyl)amido]-4,8-octadecadiene-1,3-diol (2), 1-O-beta-D- glucopyranosyl- (2S,3R,4E,8E)-2-[(2-hydroxyicosanoyl)amido]-4,8-oct adecadiene-1,3-diol (4), and 1-O-beta-D- glucopyranosyl-(2S,3R,4E,8E)-2-[(2-hydroxyoctadecanoyl )amido]-4,8- octadecadiene-1,3-diol (5), respectively. These cerebrosides displayed significant antihepatotoxic activity.

Animals↗
PubMed1996

Lacrimal canaliculus obstruction: nonsurgical treatment with a newly designed polyurethane stent.

A newly designed polyurethane stent was used to successfully treat 30 eyes (in 28 patients) with epiphora resulting from obstruction of the lacrimal canaliculus. After stent placement, epiphora resolved in all eyes. During follow-up, epiphora recurred in 20 eyes, but epiphora did not recur and the lacrimal canaliculus was patent in 12 eyes after the stent was removed. The stent appears to be valuable for nonsurgical treatment of obstruction of the lacrimal canaliculus.

Equipment Design↗
PubMed1995

Agastaquinone, a new cytotoxic diterpenoid quinone from Agastache rugosa.

A new diterpenoid quinone, agastaquinone [1], was isolated from the roots of Agastache rugosa. An oxime derivative [2] of agastaquinone was prepared with hydroxylamine hydrochloride. The structure of agastaquinone [1] was established as 7-hydroxy-12-methoxy-20-norabieta-1,5(10),6,8,12-pentaene-3,11,14- trione by spectroscopic techniques. Compounds 1 and 2 showed nonspecific cytotoxic activities against several human cancer cell lines in vitro (A549, SK-OV-3, SK-MEL-2, XF498, and HCT15).

Abietanes↗
PubMed1995

Cytotoxic compounds from a two-sponge association.

Investigation of the cytotoxic constituents of a two-sponge association (Poecillastra sp. and Jaspis sp.) led to the isolation of pectenotoxin II [1] and psammaplin A as the active compounds. In an in vitro cell culture assay, 1 displayed very potent cytotoxic activities against human lung (A-549), colon (HT-29), and breast (MCF-7) cancer cell lines. Pectenotoxin II also exhibited selective cytotoxicity against several cell lines representing ovarian, renal, lung, colon, CNS, melanoma, and breast cancer, with differences in LC50 values between sensitive and resistant cell lines of 100-fold or more.

Animals↗
PubMed1995

Signal flows from two phospholipase C-linked receptors are independent in PC12 cells.

Bradykinin (BK) receptor and P2-purinergic receptor are known to be coupled to phospholipase C (PLC) in PC12 cells. To study the interaction between these two PLC-linked receptors, the presence of both receptors on individual cells was demonstrated by sequential Ca2+ spikes caused by BK and ATP in a single fura-2-loaded cell. BK- and ATP-induced catecholamine (CA) secretions were desensitized within 5 min. However, in the sequential experiment, the BK-induced homologous desensitization of CA secretion did not block the ATP-induced secretion, and vice versa. Each agonist-induced an increase in inositol 1,4,5-trisphosphate (IP3) production and intracellular free Ca2+ concentration also led to homologous desensitization. However, there was no heterologous desensitization between the two agonists. When the cells were treated with both BK and ATP simultaneously, the amounts of CA secretion, IP3 production, internal Ca2+ mobilization, and Ca2+ influx were all additive. We also found that both IP3-induced Ca2+ release from intracellular Ca2+ stores and Ca2+ influx from extracellular space were able to release [3H]norepinephrine, and the secretion induced by both agonists was exactly additive in the absence or presence of extracellular Ca2+. The data suggest that the CA secretions caused by BK or ATP may have separate secretory pathways even though they activate identical second messenger pathways.

Adenosine Triphosphate↗
PubMed1994

Synthesis, structure, and antitumor activity of 1,3-dithiol- and 1,3-dithiolan-2-ylidenemalonatoplatinum(II) complexes.

1,3-Dithiol- and 1,3-dithiolan-2-ylidenemalonatoplatinum(II) complexes A2Pt(OOC)2C = CR2 (A = NH3, cyclopropylamine (CPA) or A2 = ethylenediamine(EDA), trans(+/-)-1,2-diaminocyclohexane(DACH); R2 = -SCH = CHS-, -SCH2CH2S-) have been synthesized and subjected to in vivo assay for antitumor activity after characterization by means of elemental analysis, IR spectroscopy, and x-ray analysis. The molecular structure of (CPA)2Pt(OOC)2C = CSCH = CHS has been determined by x-ray diffraction: space group P2(1)/n, a = 7.955(1), b = 16.912(2), c = 15.116(2) A, beta = 102.74(1) degrees, z = 4, R = 0.032, Rw = 0.035. Among the Pt(II) complexes studied, biscyclopropylamineplatinum(II) complexes both of the above-mentioned dicarboxylate leaving groups exhibited much higher antitumor activity against the leukemia L1210 cell line compared with the known cisplatin.

Animals↗
PubMed1994

Photoastigmatic refractive keratectomy in 168 eyes: six-month results.

Using a 193 nm excimer laser, we performed elliptical astigmatic and spherical corneal ablation on 168 eyes with compound myopic astigmatism and analyzed the three- and six-month postoperative results. Mean preoperative astigmatism was 1.51 +/- 0.81 diopters (D). Mean three- and six-month postoperative astigmatism was 0.70 +/- 0.58 D and 0.67 +/- 0.60 D, respectively. Six months after surgery, eyes with less than 1.00 D preoperative astigmatism improved 4.8%. The improvement was 53.5% and 59.1% for eyes with a preoperative astigmatism of 1.00 D to 2.00 D and above 3.00 D, respectively. Overall, astigmatism improved 55.6%. There was a wide distribution from overcorrection to undercorrection. Astigmatism six months after surgery was within 10 degrees of the preoperative axis in 46.1% of eyes.

Adult↗
PubMed1994

Properties of the fluorescent sodium indicator "SBFI" in rat and rabbit cardiac myocytes.

INTRODUCTION: Although some properties of the fluorescent sodium indicator "SBFI" are known, there is no accepted method by which the SBFI signal might be calibrated for intracellular Na (Nai) in cardiac cells. The first aim of this study was to characterize the loading and compartmentalization of this indicator in single cardiac myocytes. The second aim was, from experimental observation, to develop a rational calibration method for SBFI. The third aim was to use this Na indicator to study the dependence of tonic contraction on Nai in voltage-clamped ventricular myocytes. METHODS AND RESULTS: SBFI was incorporated into myocytes by incubating with the acetoxymethyl ester (10 microM) for 2 hours. This led to an intracellular concentration of SBFI free acid of 122 +/- 17 microM. We considered a number of issues with respect to compartmentalization of indicator and, under our conditions, we found the majority (71%) of indicator was situated in the cytoplasm. Therefore, SBFI indicates mainly changes of cytoplasmic Na. Calibration of the indicator for Nai was performed by equilibrating internal and external Na. We investigated the conditions required for optimum transmembrane Na equilibration and found it necessary to use a calibration solution free of both Ca and magnesium (Mg). The Na ionophores gramicidin D and monensin were both required, and it was also necessary to inhibit the Na/K pump for optimum Na equilibration. Using these conditions, the Nai concentration in quiescent rat ventricular myocytes was 10.9 +/- 0.74 mM (mean +/- SEM, n = 40; equivalent to an Na activity of 8.3 mM). The concentration of Nai was significantly lower in quiescent rabbit myocytes: 3.8 +/- 0.23 mM (n = 24; equivalent to an Na activity of 2.9 mM). In voltage-clamped rabbit myocytes, inhibition of the Na/K pump caused a rise of Nai; there were also marked effects on the tonic shortening elicited by ramp depolarizations. As Nai rose, the magnitude of tonic shortening increased and its voltage dependence also changed. CONCLUSION: These results confirm the suitability of SBFI for measuring Nai in cardiac cells. Provided that steps are taken to optimize transmembrane Na equilibration, the indicator can be calibrated for Nai. The different Nai of rat and rabbit myocytes has implications for the function of sarcolemmal Na/Ca exchange in each cell type. An Nai of 10.9 mM in rat myocytes gives a calculated reversal potential for the exchange of -35 mV. In comparison, an Nai of 3.8 mM in rabbit myocytes leads to a reversal potential for the exchange +45 mV. Therefore, relatively small changes of Nai can shift the reversal potential of the exchange to values that are substantially more positive or negative than zero. The behavior of voltage-dependent tonic contraction in rabbit myocytes was consistent with the Na/Ca exchange reversal potential being more positive than zero in these cells.

Animals↗
PubMed1993

A method for isolating rabbit atrioventricular node myocytes which retain normal morphology and function.

This report describes a method for isolating single rabbit atrioventricular (AV) node myocytes which retain their normal morphology when exposed to millimolar levels of calcium. Previous attempts to isolate cells from the AV node have produced myocytes that "round up" (i.e., go into contracture) when exposed to calcium. We show that the cells isolated with our technique possess properties similar to those described for intact AV nodal tissue. We find that single AV node myocytes are shorter and thinner (mean dimension = 103.5 +/- 2.3 by 7.8 +/- 0.2 microns; mean +/- SE, n = 90) than atrial or ventricular cells. Many of the cells produced by this isolation procedure generate spontaneous action potentials (188 +/- 9 beats/min; n = 6), which resemble action potentials recorded previously from the intact AV node. Voltage-clamp recordings from spontaneously active cells revealed similar membrane currents to those seen in intact tissue: fast sodium current and a L-type calcium current, followed by a delayed outward current. However, we found little evidence for the hyperpolarization-activated current (I(f)). Because the cells responded normally to concentrations of acetylcholine and isoproterenol within the physiological range, their cholinergic and adrenergic receptors appear to be well preserved by the isolation procedure. The ability to isolate morphologically and functionally normal AV myocytes may represent a significant advance for the investigation of nodal physiology at the cellular level.

Acetylcholine↗
PubMed1991

The role of intracellular sodium in the control of cardiac contraction.

Intracellular sodium was estimated in ventricular myocytes using the new Na-sensitive fluorescent indicator SBFI. Membrane potential and contraction were also measured simultaneously. Using an in situ calibration method, we found that intracellular sodium activity (aiNa) was 2.9 mM in quiescent rabbit cells. When the digitalis analogue strophanthidin inhibited the Na-K pump of myocytes with action potentials (APs), changes of contraction and aiNa were dissociated in time. There was also marked hysteresis between contraction and aiNa. When strophanthidin was applied to the same myocytes under voltage-clamp conditions, temporal dissociation between contraction and aiNa was dramatically reduced. This suggests that much of the dissociation and hysteresis was due the change in AP shape with strophanthidin. A small amount of residual hysteresis still existed even with voltage-clamp, and this persisted when the pump was blocked by removal of external potassium as an alternative method. We suggest that a gradient of sodium concentration from the subsarcolemmal space to the bulk cytoplasm might be responsible for hysteresis. Whereas SBFI probably signals the average Na level of the cytoplasm, subsarcolemmal Na may control Ca influx and contraction via Na-Ca exchange.

Action Potentials↗
PubMed1990

Effect of norepinephrine on Na(+)-K+ pump and Na+ influx in sheep cardiac Purkinje fibers.

Effects of norepinephrine and Ca+ on Na(+)-K+ pump and pacemaker current were investigated by simultaneous measurement of intracellular Na+ activity (aiNa) and membrane potential in driven (1 Hz) and quiescent sheep cardiac Purkinje fibers. Concurrently, twitch force was measured in driven fibers, in which norepinephrine (NE) produced a decrease in aiNa, a prolongation in action potential duration, and a hyperpolarization in diastolic membrane potential, Vdm. In contrast, in quiescent fibers, NE produced an increase in aiNa and a depolarization in resting membrane potential, Vm. The decrease in aiNa, prolongation in action potential duration, and hyperpolarization in Vdm produced by NE were blocked by 5 x 10(-6) M strophanthidin, presumably through inhibition of the Na(+)-K+ pump. The increase in aiNa and membrane depolarization caused by NE were abolished by high [K+]o or Cs+, presumably through inhibition of the pacemaker current, if. These results indicate that in driven fibers NE stimulates predominantly the Na(+)-K+ pump, producing a decrease in aiNa and that in quiescent fibers it increases predominantly if, producing an increase in aiNa. The effect of NE on driven and quiescent fibers differs because of the voltage dependence of if and perhaps the Na(+)-K+ pump. Consequently, the relative magnitude of the two opposing effects of NE on aiNa appears to be dependent on membrane potential. In quiescent fibers, Cs+ monotonically decreased aiNa to a steady-state value, while Cs+ hyperpolarized membrane potential and then slowly depolarized to a steady-state level, producing a transient hyperpolarization. In driven fibers, Cs+ decreased aiNa, shortened action potential duration, and depolarized Vdm. Cs+ decreased aiNa more in quiescent fibers than in driven fibers. The decrease in aiNa and hyperpolarization in membrane potential produced by Cs+ in quiescent fibers were abolished by depolarization induced by high K+ extracellular concentration (25.4 mM) but were not abolished or reduced by 5 x 10(-6) M strophanthidin. These results suggest that the decrease in aiNa and hyperpolarization in membrane potential by Cs+ are caused by blockage of if but not by stimulation of the Na(+)-K+ pump and that if is an important source of Na+ loading into cells.

Action Potentials↗
PubMed1988

Na+-Ca2+ exchange in regulation of contractility in canine cardiac Purkinje fibers.

To study Na+-Ca2+ exchange, intracellular Na+ activity (aiNa), twitch tension, and transmembrane potential were simultaneously measured in canine cardiac Purkinje fibers driven at a constant rate (1 Hz) in the absence and presence of strophanthidin (5 X 10(-7) M) at normal, low, and high extracellular [Na+] ([Na+]o) or [Ca2+] ([Ca2+]o). Intracellular Ca2+ activity (aiCa) of the fibers was also measured in a normal Tyrode solution. Reductions of [Na+]o by 20, 40, and 60% decreased the ratio of extracellular Na+ activity (aoNa) and aiNa in the steady state but steeply increased twitch tension. This finding is consistent with the view that a decrease in aoNa/aiNa increases intracellular Ca2+ through Na+-Ca2+ exchange. In further agreement with this view, a Na+-free solution virtually depleted intracellular Na+ and increased the resting tension of the fibers. The slope of the relation of the logs of twitch tension and aiNa that was determined at normal [Na+]o and [Ca2+]o may reflect the properties of the Na+-Ca2+ exchange. Slope of log tension-aiNa relationship decreased when reducing [Na+]o or increasing [Ca2+]o had decreased the level of aiNa. On the other hand, the slope increased when a rise in [Na+]o or a reduction in [Ca2+]o had increased the level of aiNa. These results indicate that as the aiNa level increased, slope of tension-aiNa relation increased, which suggests that Na+-Ca2+ exchange may depend on level of aiNa.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Role of aiNa in positive force-frequency staircase in guinea pig papillary muscle.

In the ventricular papillary muscle of guinea pig heart, membrane potential, intracellular sodium activity (aiNa), and twitch force were measured simultaneously and continuously for many hours at stimulation rates of 0, 0.5, 1, 2, 3, 4, 5, and 6 Hz to investigate the relation of aiNa to twitch force and membrane potential both in the steady state and during the changes in these variables. After an increase in stimulation rate, both aiNa and twitch force increased progressively, reaching steady-state levels. The relation between twitch force and aiNa in the steady state was generally sigmoidal over the range of 0.5-5 Hz and steep in the 1- to 4-Hz range. After either increase or decrease in stimulation rate, the time course of change in aiNa was exponential and similar to that of change in twitch force. Moreover, the force-aiNa relation observed after increase in stimulation rate from 0.5 to 3 Hz resembled that observed after decrease in the rate from 3 to 0.5 Hz, indicating an absence of hysteresis in the relation. The results suggest that an increase in aiNa is an important factor involved in the force staircase. As stimulation rate was increased from 0.5 to higher rates (5 or 6 Hz) and then decreased back to 0.5 Hz, a hysteresis phenomenon was observed in the relation between twitch force and aiNa. This suggests that some secondary factor may alter the relation between twitch force and aiNa. As stimulation rate increased and aiNa rose, the steady-state diastolic membrane potential hyperpolarized. This result is consistent with the view that an increase in aiNa enhances the electrogenic Na+-K+ pump and hyperpolarizes the cell membrane.

Action Potentials↗
PubMed1988

Regulation of cytosolic free calcium in isolated perfused proximal tubules of Necturus.

To study the role of intracellular Ca2+ in regulating renal tubular transport of ions and water, cytosolic calcium ion activity (aiCa), cytosolic sodium ion activity (aiNa), and intracellular pH (pHi) in cells of isolated perfused proximal tubules of Necturus kidney were measured with Ca2+-, Na+-, and H+-selective microelectrodes, respectively. In control conditions, i.e., HCO3-Ringer solution on both sides of the epithelium, aiCa was 82 +/- 7 (SE) nM (n = 54), aiNa averaged 12.8 +/- 0.4 mM (n = 53), and pHi was 7.33 +/- 0.03 (n = 27). When the Na-K pump was inhibited by nominally K-free Ringer circumfusion, aiCa increased from a control level of 75 +/- 13 to 237 +/- 40 nM (paired t test; n = 16; P less than 0.001); in a different set of tubules, aiNa rose from 11.3 +/- 0.6 to 51.5 +/- 5.8 mM (n = 11; P less than 0.001). When organic solutes were deleted in the luminal perfusate, aiCa decreased from 73 +/- 11 to 61 +/- 11 nM (n = 9; P less than 0.001) and aiNa decreased from 14.6 +/- 0.6 to 8.3 +/- 0.7 mM (n = 9; P less than 0.001). Depolarization of the peritubular cell membrane with high-K, low-Na Ringer decreased aiCa from 90 +/- 12 to 55 +/- 9 nM (n = 13; P less than 0.001) and reduced aiNa from 13.1 +/- 1.0 to 7.5 +/- 0.6 mM (n = 16; P less than 0.001). Ionomycin (2 X 10(-6) M) increased aiCa from 67 +/- 10 to 158 +/- 26 nM (n = 10; P less than 0.001) and pHi from 7.33 +/- 0.03 to 7.39 +/- 0.03 (n = 27; P less than 0.001) but reduced aiNa from 11.8 +/- 0.9 to 10.3 +/- 0.7 mM (n = 11; P less than 0.001). The data are consistent with the view that aiCa is determined, in part, by the magnitude of the electrochemical potential gradient for Na ions across the basolateral cell membrane.

Animals↗
PubMed1988

Measurement of cytosolic calcium: ion selective microelectrodes.

Since the Ca2+-selective neutral carrier was introduced in 1972, Ca2+-selective microelectrodes have been made and used for measurement of Ca2+ activity (effective Ca2+ concentration) in the cytoplasm. Over the last several years, application of the technique has provided valuable information about resting levels and changes of cytosolic Ca2+ activity. This article reviews technical aspects of the electrodes, including their construction, calibration, and determination of cytosolic Ca2+ activity. The Ca2+-selective microelectrodes successfully prepared show the voltage responses of about 20 mV between 10(-6) and 10(-7) M Ca2+, and about 10 mV between 10(-7) and 10(-8) M Ca2+ so that they could be used to monitor changes in cytosolic free Ca2+. However, the techniques of the electrodes are still difficult as compared with those of other ion-selective microelectrodes. Some advantages and disadvantages of the techniques are discussed.

Animals↗