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Biomedical subjects

S T Tan

Publications and source records attributed to S T Tan.

50 records · Page 3Linked to original sources
PubMed1986

Simple method to demonstrate radiation-inducible radiation resistance in microbial cells.

A simple method for detection of radiation-inducible radiation resistance was developed by irradiating aliquots (0.01 ml) of cell suspension on agar plates. Part of each experimental plate was subjected to an induction treatment, and subsequent radiation resistance was compared with that of untreated cells on the same plate. The UV radiation resistance of a Micrococcus sp. was increased approximately 1.6 times by an induction treatment. This simple procedure of irradiating cells in a "fixed" position on agar avoided washing, centrifugation, and cell enumeration required in traditional methods.

Agar↗
PubMed1986

Effect of acute experimental colitis on rabbit colonic smooth muscle.

The membrane potential and contractile activity of colonic circular smooth muscle from New Zealand White rabbits were studied after the production of acute experimental colitis. Colitis was induced in the distal colon by rectal infusion of formaldehyde solution, followed by an intravenous bolus of soluble immune complexes. Despite active mucosal inflammation, there are only occasional inflammatory cells in the muscularis. Electrophysiological studies on tissue from control rabbits and rabbits with colitis were performed using double sucrose gap and intracellular microelectrode techniques. The resting membrane potential was lower (-44 +/- 3 mV) in muscle from rabbits with colitis compared with control animals (-54 +/- 2 mV) (P less than 0.02). Amplitude of the electrotonic potential after a hyperpolarizing current pulse was decreased (P less than 0.05) and the time constant was shortened (P less than 0.01) in muscle from animals with colitis compared with normal animals. Amplitude (13.1 +/- 2.3 mV) and maximum rate of rise (0.24 +/- 0.06 V/s) of the spike potential, initiated by a depolarizing current pulse, were decreased in muscle from animals with colitis compared with muscle from healthy animals (P less than 0.001). Isometric tension generation after electrical and chemical depolarization of the membrane or bethanechol administration was decreased (P less than 0.001) in muscle from colitic animals. These studies suggest 1) membrane resistance and membrane potential are decreased in muscle strips from animals with colitis; and 2) there is a disturbance in the electrical and mechanical response of these tissues after stimulation.

Action Potentials↗
PubMed1985

Role of sodium or calcium in electrical depolarization of feline colonic smooth muscle.

The aim of this study was to compare the role of Na+ and Ca2+ on the membrane potential and contraction of feline colonic circular smooth muscle. The changes in membrane potential were correlated with a change in tension using the double-sucrose gap technique. The estimated resting potential was -62.8 +/- 2.6 mV. A depolarizing current, passed during quiescent periods of the membrane, stimulated a spike potential and caused a concomitant increase in smooth muscle tension. The maximum depolarization rate of the active spike potential was rapid (580 +/- 75 mV/s) and unaffected by the amplitude of the depolarizing current. Reduction of extracellular calcium (0.0 mM Ca2+ plus 5 mM EGTA) or blockade of the calcium channels with verapamil (10(-6)M) slowed the maximum rate of membrane depolarization to 128 +/- 20 mV/s (P less than 0.001). The steady-state amplitude of the electrotonic potential and time constant also decreased in low-calcium solutions. The amplitude of smooth muscle contraction and the time between stimulus and onset of contraction were dependent on the amplitude of the depolarizing current and the concentration of extracellular calcium. Removal of sodium had no effect on the electrotonic potentials, maximum dV/dt of the spike, or the contraction of the smooth muscle. These studies suggest calcium plays a major role in the generation of an active spike potential, colonic smooth muscle contraction requires extracellular calcium and is associated with an active regenerative spike potential, and sodium plays a minor role in the generation of an active spike potential and in the initiation of a contraction in feline colonic smooth muscle.

Action Potentials↗
PubMed1983

Paper replication method for isolation of radiation-sensitive mutants.

A filter paper replication system particularly useful for isolation of radiation-sensitive mutants of pigmented bacteria was devised. The fidelity of replication was high. Adhesion between a paper disk and a properly dried master plate provided adequate contact pressure. The replicas arising from this technique constitute a convenient apparatus for general application in isolation of clones sensitive to a discriminating treatment.

Bacteriological Techniques↗
PubMed1982

Direct measurement of sarcomere length from isolated cardiac cells.

Isolated cardiac muscle cells enzymatically digested with collagenase and hyaluronidase from whole rat myocardium demonstrate the characteristics of an intact membrane in that they tolerate millimolar concentrations of free Ca2+ and exhibit phasic contractions with electrical excitation. These isolated cells maintain their characteristic A-I band striation patterns when at rest or during contraction. An apparatus has been developed to directly image these cells with phase-contrast micrography onto a 1,728-element charge-coupled device photodiode array for rapid data storage in a digital computer. The digitized striation pattern profile was analyzed for individual and average sarcomere spacing. In isotonic media the average resting sarcomere length ranged from 1.77 to 1.91 micrometers in 13 cells, with a mean length of 1.83 +/- 0.12 micrometers. Electrically stimulated phasic contractions in three cells demonstrated a synchronous 20% decrease in sarcomere spacing to a mean of 1.51 micrometers. Striation spacing decreased under hypertonic stress but elongated only up to 1.93 micrometers in hypotonic solutions, suggesting that some internal elastic constraint exists that limits elongation of the cell.

Animals↗
PubMed1981

Perturbation measurements of papillary muscle elasticity.

Small step-length perturbations (less than 0.5% Lmax) have been applied to rabbit papillary muscle for the purpose of measuring muscle stiffness at rest and during isometric twitch-force development. These stiffness-force measurements were fitted to four mechanical analogs to evaluate whether any of the models adequately predict the mechanical properties of papillary muscle. Stiffness-force relations have been measured at varied initial muscle lengths so that a broad range of applicability of an analog could be evaluated. This study shows that none of the four experimentally definable analogs predicts the stiffness-force responses of the muscle over a physiological range of initial muscle lengths. A two-segment nonhomogeneous analog has the same stiffness-force characteristics as a six-parameter lumped model but cannot be differentiated from the lumped model without a measurement of segmental variations. It is concluded that the passive elastic elements of papillary muscle cannot be controlled only by the manipulation of total muscle length so as to deduce cross-bridge mechanical properties from whole-muscle measurements.

Animals↗
PubMed1979

Contractile force measured in unskinned isolated adult rat heart fibres.

A number of investigators have succeeded in preparing isolated cardiac cells by enzymatic digestion which tolerate external [Ca2+] in the millimolar range. However, a persistent problem with these preparations is that, unlike in situ adult ventricular fibres, the isolated fibres usually beat spontaneously. This spontaneity suggests persistent ionic leakage not present in situ. A preferable preparation for mechanical and electrical studies would be one which is quiescent but excitable in response to electrical stimulation and which does not undergo contracture with repeated stimulation. We report here a modified method of cardiac fibre isolation and perfusion which leaves the fibre membrane electrically excitable and moderately resistant to mechanical stress so that the attachment of suction micropipettes to the fibre is possible for force measurement and length control. Force generation in single isolated adult rat heart fibres is consistent with in situ contractile force. The negative staircase effect (treppe) characteristic of adult not heart tissue is present with increased frequency of stimulation. Isometric developed tension increases with fibre length as in in situ ventricular tissue.

Animals↗
PubMed1979

Multiple intracellular peptidases in Neurospora crassa.

Neurospora crassa possesses multiple intracellular peptidases which display overlapping substrate specificities. They were readily detected by an in situ staining procedure for peptidases separated in polyacrylamide gels, within which the auxilliary enzyme, l-amino acid oxidase, was immobilized. Eleven different intracellular peptidases were identified by electrophoretic separation and verified by their individual patterns of substrate specificities. Most peptide substrates tested were hydrolyzed by several different peptidases. The multiple intracellular peptidases may play overlapping roles in several basic cell processes which involve peptidase activity. The amount of peptidase activity for leucylglycine present in crude extracts of cells grown under widely different conditions was relatively constant, suggesting that this enzyme may be constitutive, although alterations in the amounts of individual peptidase isozymes may occur. A single enzyme, designated peptidase II, was partially purified and obtained free from the other peptidase species. Peptidase II was found to be an aminopeptidase with activity toward many peptides of varied composition and size. It was more active with tripeptides than homologous dipeptides and showed strong activity toward methionine-containing peptides. This enzyme, with a molecular weight of about 37,000, was thermolabile at 65 degrees C and was strongly inhibited by p-hydroxymercuribenzoate, Zn(2+), Co(2+), and Mn(2+), but was insensitive to the serine protease inhibitor phenylmethylsulfonyl fluoride. Peptidase II apparently possesses an essential sulfhydryl group and may be a metalloenzyme.

Aminopeptidases↗
PubMed1975

Correlation of the glycoside response, the force staircase, and the action potential configuration in the neonatal rat heart.

The rat heart demonstrates marked alterations in its responses to ouabain and increased frequencies of stimulation and in the duration of its action potential during the initial 21 days of life. At an age of 6.2 days 5 times 10- minus 5M ouabain produced a 158.2% increase in dP/dt compared with a 17.2% increase at 21.1 days (P less than 0.001). At 6.2 days dP/dt increased by 53.4% when the heart rate was accelerated from 30 to 90 beats/min compared with an increase of 12.2% at 21.1 days (P less than 0.005). The positive glycoside and staircase responses at the younger age were virtually eliminated when the hearts were perfused with a solution containing 50% [Na+]o and 25% [Ca-2+]o ([Ca-2+]o/[Na+]o-2 maintained constant). The duration of the ventricular action potential progressively decreased from 350-400 msec at birth to 100-150 msec at 21 days of life. This decrease was due to a shortening and a decrease in the potential level of the plateau phase. The prominent plateau typical of the early neonatal period was significantly diminished by perfusion with 50% [Na+]o. The results suggest that Na+ flux through a slow membrane channel plays a significant role in the positive staircase and glycoside responses of the early neonatal rat heart. As the heart matures and becomes functionally anomalous relative to other mammalian species, the slow channel progressively closes.

Action Potentials↗
PubMed1966

The ionic dependence of cardiac excitability and contractility.

In contrast to the large volume of data supporting the dependence of cardiac excitability and phasic contractility on external Na, Van der Kloot and Rubin (1962) and Singh (1962) have reported the persistence of both electrical and phasic mechanical activity in frog atrial and ventricular preparations soaked in isotonic sucrose solutions. The acute ionic dependence of excitability and contractility in small frog atrial trabeculae has been investigated with the conclusion that excitability and phasic contractions may continue for extended periods of time in sucrose media if the extracellular ionic concentrations remain above 2% of normal. This behavior is attributed to the slow exchange properties of the cell surfaces of the frog cardiac trabeculae and the antagonistic effects of Na, K, and Ca ions on both membrane excitability and fiber contractility.

Animals↗
PubMedDate not supplied

Recurrent orf in an immunocompromised host.

A 30-year-old farmer with Nezelof's syndrome developed a giant orf on his hand. Recurrence followed surgical excision. Three excisions and split skin grafts were required before its eradication. He re-presented 8 years later with a further orf on the finger of his opposite hand. This lesion had not grown to the exuberant proportion of the previous lesion, but it defied repeated excisions, and various medical therapies including idoxuridine, interferon and transfer factor. Excision with hypochlorite dressings perioperatively and delayed split skin grafting led to eventual eradication.

Adult↗
PubMedDate not supplied

Patterns of acute respiratory tract infection in children: a longitudinal study in a depressed community in Metro Manila.

The incidences of acute respiratory tract infection (ARI) and acute lower respiratory infection (ALRI) were 6.1 and 0.5 per child-year, respectively, in children less than 5 years old in a depressed urban community in Manila. The peak age-specific incidence occurred in those children 6-23 months old for ARI and 6-11 months old for ALRI. Age less than 2 years, malnutrition, household crowding, and parental smoking were associated with a statistically significant, though modest, increase in ARI morbidity. The crude mortality rate was 14.3 per 1,000 children 0-4 years old, with a corresponding ARI-specific mortality rate of 8.9 per 1,000. The prevalence of viral infection was 32.8 and that of bacteremic ALRI was 6.7 per 1,000 children with moderate ALRI. Respiratory syncytial virus was the predominant viral pathogen, while Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus were the most frequently isolated bacterial pathogens. Transmission of respiratory pathogens in depressed communities, facilitated by inadequate housing, inaccessible health services, and prevalent malnutrition, will continue unless meaningful socioeconomic improvement is realized.

Acute Disease↗
PubMedDate not supplied

"Pentazepam" (pentazocine + diazepam) supplementing local analgesia for laparoscopic sterilization.

Salpingectomy by laparoscopy in 200 healthy outpatients employed local analgesia and "pentazepam" (pentazocine 90 mg and diazepam 30 mg in 250 ml of 5% D/W) as anesthesia. Patients received no premedication, ventilated spontaneously, without tracheal intubation, but were given nasal O2 at 3 L/min throughout the procedure. N2O was used for abdominal insufflation, and the abdominal pressure and Trendelenburg position were restricted to less than 20 cm H2O pressure and 30 degrees, respectively. Changes in arterial blood gases measured in 12 patients were unremarkable. Prolonged recovery, unsatisfactory surgical conditions, tachycardia, nausea and vomiting were infrequent.

Adult↗