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Biomedical subjects

S Kaplan

Publications and source records attributed to S Kaplan.

At least 271 records · Page 15Linked to original sources
PubMed1987

Membrane adenosine triphosphatase in synchronous cultures of Rhodobacter sphaeroides.

Studies of intracytoplasmic membrane biogenesis utilizing synchronized cultures of Rhodobacter sphaeroides have revealed that most intracytoplasmic membrane proteins accumulate continuously throughout the cell cycle while new phospholipid appears discontinuously within the intracytoplasmic membrane. The resulting changes in the structure of the membrane lipids was proposed to influence the activities of enzymes associated with the intracytoplasmic membranes (Wraight, C.A., Leuking, D.R., Fraley, R.T. and Kaplan, S. (1978) J. Biol. Chem. 253, 465-471). We have extended the study of intracytoplasmic membrane biogenesis in R. sphaeroides to include the membrane adenosine triphosphatase. The membrane bound Mg2+-dependent, oligomycin-sensitive adenosine triphosphatase activity was measured throughout the cell cycle for steady-state synchronized cells of R. sphaeroides and found to accumulate discontinuously. Following treatment with an uncoupling reagent (2,4-dinitrophenol) the intracytoplasmic membrane associated adenosine triphosphatase activity was stimulated uniformly in membranes isolated at different stages of the cell cycle. The adenosine triphosphatase was also measured by quantitative immunoblots utilizing specific antibody to compare the enzyme activity and enzyme protein mass. Immunologic measurement of the adenosine triphosphatase in isolated membranes indicated a constant ratio of enzyme to chromatophore protein exists during the cell cycle in contrast to the discontinuous accumulation of adenosine triphosphatase activity. These results are discussed in light of the cell-cycle specific synthesis of the intracytoplasmic membrane.

Adenosine Triphosphatases↗
PubMed1987

Correlates of coronary artery aneurysm formation in patients with Kawasaki disease.

Factors potentially associated with the formation or prevention of coronary artery aneurysms were investigated in 77 children with Kawasaki disease. The patients were divided into two groups. Group A consisted of those who developed coronary artery aneurysms and group B consisted of those who did not. The patients who developed aneurysms had a significantly longer duration of fever and a significantly lower minimum hemoglobin concentration than those who did not develop aneurysm. In patients who developed aneurysms, aspirin therapy was begun significantly later in the course of the illness compared with those who did not develop aneurysms. We suggest that the timing of the initiation of aspirin therapy may be important in the prevention of coronary artery aneurysms in patients with Kawasaki disease. We believe that it may be important to establish the diagnosis of Kawasaki disease as early as possible and to institute aspirin therapy at an appropriate dosage.

Adolescent↗
PubMed1987

A histologic study of laser-induced transmyocardial channels.

Carbon dioxide lasers are reported to provide ischemic myocardium direct access to blood within the ventricular cavity by inducing transmyocardial channels which maintain patency in long-term experiments. We have histologically examined the natural history of channels produced with this technique and compared them with transmyocardial channels created by needle puncture. Immediately after application of the laser, four concentric zones vaporization, carbonization, fixation, and transition could be distinguished along the transmyocardial path. Needle puncture channels were fully occluded within 48 hr, whereas laser-induced channels maintained partial patency for a 2-week period, after which they also became occluded. It appears likely that the instantaneous vaporization produced by the laser may delay the release of factors which mediate the healing process, but occlusion of channels was universal in this study. It remains to be determined whether or not variables such as wattage, beam diameter, or tissue temperature influence long-term channel patency.

Animals↗
PubMed1987

Correlates of resting and maximal exercise systolic blood pressure after repair of coarctation of the aorta: a multivariable analysis.

Repair of coarctation of the aorta may not prevent the subsequent development of elevated systemic blood pressure at rest or with exercise. The correlates of late postoperative resting systolic blood pressure and maximal exercise systolic blood pressure levels were investigated in a retrospective study of 42 patients who had graded exercise tests after correction of coarctation of the aorta. The independent variables studied included height, weight, body surface area, age at surgery, age at exercise testing, the time interval between surgery and exercise testing, the highest systolic blood pressure prior to surgery, gradient across the coarctation at preoperative catheterization, and the residual postoperative gradient across the coarctation. The same combination of independent variables provided the best regression model for explanation of the variance of both postoperative resting and maximal exercise systolic blood pressure. The models included height, highest preoperative systolic blood pressure, and residual gradient. None of the other variables added significant explanatory ability to either model. These findings suggest that the preoperative level of systolic blood pressure may be the best determinant of timing the corrective surgery. It may be possible to defer the operation, as long as blood pressure remains normal, until an age when repair is less likely to result in recurrent coarctation.

Adolescent↗
PubMed1987

Age-related digoxin effects in an intact canine model.

The inotropic and electrophysiologic effects of digoxin were studied in anesthetized neonatal and adult dogs to test the hypothesis that digoxin had comparable effects in these groups. Recordings of the ECG and central arterial pressure were made starting at 5.75 hours after an intravenous injection of 50 micrograms/kg of the drug. Parameters measured were heart rate (HR); PR interval; mean, systolic, and diastolic blood pressure; preejection period (PEP); and ejection time (ET). Two indices of systolic function were calculated, the systolic time interval (STI = PEP/ET) and total electromechanical systole (TMS = PEP + ET), which was indexed for HR. There was no significant difference from control animals in either the adult or neonatal groups in the PR interval or blood pressure. In the neonatal dogs, HR and STI were also not significantly different from control. However, in the neonatal dogs, there was a significant decrease in the indexed TMS, 288 +/- 7 vs 270 +/- 11 msec (p less than 0.01). In the adult animals, HR decreased from 116 +/- 35 to 66 +/- 25 bpm (p less than 0.01), STI decreased from 0.559 +/- 0.059 to 0.447 +/- 0.069 (p less than 0.01), and indexed TMS decreased from 333 +/- 10 to 291 +/- 13 msec (p less than 0.001). Two-way analysis of variance demonstrated that digoxin differed significantly in its effects on HR (p = 0.005), STI (p = 0.018), and TMS indexed for HR (p = 0.003) in neonatal compared to adult dogs. Pharmacokinetic studies showed a rapid distribution phase and equilibrium conditions at the time of physiologic measurements.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1987

Predictors of postoperative ventricular dysfunction in infants who have undergone primary repair of a ventricular septal defect.

By means of postoperative radionuclide angiography we identified a subset of infants undergoing primary repair of their ventricular septal defects (VSD) who had postoperative morbidity and ventricular dysfunction. Twenty-three consecutive infants undergoing repair of an uncomplicated VSD were studied. Radionuclide-determined postoperative ventricular dysfunction (VD), as defined by a left ventricular ejection fraction less than 0.30 2 to 4 hours after surgery, was correlated with clinical signs of postoperative morbidity. Six patients developed postoperative VD. Clinical correlates of VD included the use of postoperative inotropic support, increased number of postoperative intensive care days, and a low growth rate 3 months postoperatively. Potential predictors of VD were evaluated. A preoperative pulmonary-to-systemic blood flow ratio (Qp/Qs) greater than 3.0 and a pulmonary-to-systemic vascular resistance ratio (Rp/Rs) less than 0.20, taken in combination, gave a positive predictive value for VD of 100%. It is concluded that the preoperative Qp/Qs and Rp/Rs can be used to predict those infants at risk for postoperative morbidity following repair of their VSD.

Cardiac Catheterization↗
PubMed1987

Comparison of dose frequency of human growth hormone in treatment of organic and idiopathic hypopituitarism.

Two weekly (biw) injections of pituitary human growth hormone (hGH) were compared with three weekly (tiw) injections of hGH (0.24 IU hGH/kg body weight/wk for both groups) for effect on growth rate in children with idiopathic and organic hypopituitarism. Both dosage schedules resulted in increased growth rate during the first 12 months of therapy; the tiw dosage was more effective in the first 6 months in patients with organic hypopituitarism, and in the second 6 months in patients with idiopathic hypopituitarism. There was no advantage to tiw therapy during the second year of therapy in either group. The additional increment in height after 1 year of therapy using tiw compared with biw therapy was 2 cm and 1 cm for the patients with organic and idiopathic hypopituitarism, respectively. This increment should be weighed against the cost, pain, and inconvenience of tiw versus biw doses of hGH in the treatment of hGH deficiency. With the dosages used in this study, tiw therapy was more effective during the first year, when patients are more responsive, and should be recommended. Twice weekly therapy could be considered for the second and possibly subsequent years of therapy. Other schedules of treatment may be more effective than either of these schedules.

Child↗
PubMed1987

Estimation of long-term risk from Canadian uranium mill tailings.

A methodology is presented for assessing the risk from Canadian uranium mill tailings piles. The methodology is based on the "set of triplets" concept and uses an event tree to identify various scenarios representing the performance of a pile over its 1,000-year design life. Compartment-type mathematical models are used to quantify the movement of hazardous substances through the environment. Numerical examples are given of both "level 1" (straight probabilistic) and "level 2" (probability of frequency) type analyses.

Canada↗
PubMed1987

On the use of the cause table in handling common cause events in system analysis.

A method is presented for applying the cause table concept to the problem of common cause events. This method can be regarded as an alternative to the approach in which these events are included directly into the system fault trees. In comparison with this approach, the cause table method offers the advantage of simple fault trees, convenient visibility of the contributions of causes, and the ability to truncate the numerical calculation conveniently by aggregating small terms into an "other" category. Generally speaking, the cause table method can be said to handle common causes at the level of arithmetic (i.e., numbers) rather than at the level of algebra (determining cutsets and frequency equations).

Methods↗
PubMed1987

DNA sequence and in vitro expression of the B875 light-harvesting polypeptides of Rhodobacter sphaeroides.

The genes for the Rhodobacter sphaeroides light-harvesting B875-beta, and B875-alpha polypeptides (pufB and pufA) are closely linked to the genes for the reaction center L and reaction center M polypeptides (pufL and pufM) on what has been termed the puf operon (gene order, pufB, A, L, M). The DNA sequence of the pufB and pufA structural genes from wild-type R. sphaeroides 2.4.1 was determined and aligned with the available amino acid sequence of the wild-type B875-beta and B875-alpha polypeptides. The relative levels of the B875-beta and B875-alpha and the reaction center L and reaction center M polypeptides synthesized in a homologous cell-free transcription-translation system were compared with those found in vivo. Analysis of the gene products produced in vitro with plasmids containing deletions upstream of the pufB structural gene identified a region of DNA required for expression of the B875-beta and B875-alpha polypeptides. These results support the hypothesis that the mapped 5' termini of the large and small puf operon transcripts represent transcription initiation sites.

Amino Acid Sequence↗
PubMed1987

Cloning, DNA sequence, and expression of the Rhodobacter sphaeroides light-harvesting B800-850-alpha and B800-850-beta genes.

Two deoxyoligonucleotide probes were synthesized in accordance with the available amino acid sequence of the B800-850-beta polypeptide from Rhodobacter sphaeroides and were used to isolate a 2.6-kilobase PstI fragment from R. sphaeroides 2.4.1 chromosomal DNA. Identification of the B800-850-beta and B800-850-alpha structural genes, pucB and pucA, was confirmed by DNA sequencing. Northern (RNA) blot analysis, using restriction endonuclease fragments from the cloned genes as probes, revealed a single puc-operon-specific, highly stable transcript of approximately 640 bases present in photosynthetically grown cells. In vitro transcription-translation analysis of the puc operon revealed that the maximum synthesis of the puc operon gene products was achieved when the entire 2.6-kilobase PstI fragment was used as the template, although a 537-base-pair XmaIII fragment was sufficient to direct the synthesis of pucB and pucA fusion product.

Amino Acid Sequence↗
PubMed1987

Cloning of the gene for phosphoribulokinase activity from Rhodobacter sphaeroides and its expression in Escherichia coli.

A 3.4-kilobase EcoRI restriction endonuclease fragment has been cloned from the facultatively photoheterotrophic bacterium Rhodobacter sphaeroides and shown to contain the structural gene (prkA) for phosphoribulokinase (PRK) activity. The PRK activity was characterized in Escherichia coli, and the product of the reaction was identified. The prkA gene was localized to a 1,565-base-pair EcoRI-PstI restriction endonuclease fragment and gave rise to a 33-kilodalton polypeptide both in vivo and in vitro. The gene product produced in E. coli was shown to be identical to the gene product produced in R. sphaeroides. The amino acid sequence for the amino-terminal region deduced from the DNA sequence confirmed that derived for partially purified PRK derived from both E. coli and R. sphaeroides. In addition, the 3.4-kilobase EcoRI restriction endonuclease fragment coded for a 37-kilodalton polypeptide of unknown function, and preliminary evidence indicates that this DNA fragment is linked to genes coding for other activities significant in photosynthetic carbon assimilation. The genetic organization and proposed operon structure of this DNA fragment are discussed.

Base Sequence↗
PubMed1987

EEG monitoring during paroxysmal hyperpnea of tetralogy of Fallot: an epileptic or hypoxic phenomenon?

We describe a neurologically compromised infant with tetralogy of Fallot who was having multiple paroxysmal episodes of hypotonia, eye rolling, stiffening, and loss of consciousness. Simultaneous electroencephalography with video monitoring was used to determine if these episodes were a primary epileptic phenomenon or the result of hypoxic central nervous system involvement from paroxysms of hyperpnea and cyanosis. The findings would suggest that the paroxysmal episodes were not primarily epileptic. The electroencephalographic findings during the spell were similar to those found with hypoxia due to other causes. This may have physiological and therapeutic significance and be useful in following other infants with congenital heart disease who have similar episodes, especially when the infants have significant risk factors for seizures.

Diagnosis, Differential↗
PubMed1986

Origin of the mRNA stoichiometry of the puf operon in Rhodobacter sphaeroides.

The LH-I structural genes are located 5' of the RC-L and -M structural genes on what has been designated as the puf operon of Rhodobacter sphaeroides. Analysis of puf operon expression in R. sphaeroides by Northern hybridization with probes specific for individual structural gene has identified two transcripts encoded by this operon. The large (2.6 kilobase pairs (kb] transcript contains sequences for all four polypeptides of the puf operon, whereas the small (0.5 kb) transcript, which is more abundant (10-15-fold) than the large transcript under photosynthetic growth, is homologous only to the two LH-I structural genes. Transcription of the puf operon during photosynthetic growth under saturating light conditions is increased approximately 3-fold relative to growth in the presence of oxygen while the relative ratio of these two transcripts is independent of the incident light intensity. Analysis of the turnover of the two transcripts (t1/2 of 9 and 20 min for the large and small transcripts, respectively) indicates that 5' processing is the initial step in the degradation of the large transcript and that the molar excess of the small transcript cannot be accounted for by differences in the rates of turnover of these two mRNA species. Analysis of the 5' ends of the 2.6- and 0.5-kb transcripts, their relative abundance, and stabilities indicates that these two transcripts have different 5'-ends corresponding to 75 and 104 base pairs upstream from the start of the LH-I beta structural gene, respectively. Northern hybridization analysis with specific synthetic deoxyoligonucleotide probes confirmed that the two transcripts differ by 29 bases at their 5'-ends, suggesting that differential transcript initiation may be involved in regulating the relative levels of these two mRNA species in vivo, although we cannot rule out complex mechanisms of post-transcriptional processing.

Bacterial Proteins↗
PubMed1986

Phospholipid transfer activity in synchronous populations of Rhodobacter sphaeroides.

Studies of intracytoplasmic membrane biogenesis employing steady-state synchronously dividing populations of Rhodobacter sphaeroides reveal that the translocation of pre-existing phospholipid into the growing membrane is concurrent with cell division (Cain, B.D., Deal, C.D., Fraley, R.T. and Kaplan, S. (1981) J. Bacteriol. 145, 1154-1166), yet the mechanism of phospholipid movement is unknown. However, the discovery of phospholipid transfer protein activity in R. sphaeroides (Cohen, L.K., Lueking, D.R. and Kaplan, S. (1979) J. Biol. Chem. 254, 721-728) provides one possible mechanism for phospholipid movement. Therefore the level of phospholipid transfer activity in cell lysates of synchronized cultures was measured and was shown to increase stepwise coinciding precisely with the increase in cell number of the culture. Although the amount of transfer activity per cell remained constant throughout the cell cycle, the specific activity of the phospholipid transfer activity showed a cyclical oscillation with its highest value coincident with the completion of cell division. Purified intracytoplasmic membrane can be used as phospholipid acceptor in the developed phospholipid transfer assay by employing either cytoplasmic membrane or liposomes as the phospholipid donor. Intracytoplasmic membrane isolated from the cells prior to division (high protein to phospholipid ratio) served as a better phospholipid acceptor in the phospholipid transfer system when compared with membranes derived from the cells following cell division (low protein to phospholipid ratio).

Chromatophores↗
PubMed1986

Double-lumen, silicone rubber, indwelling venous catheters. A new modality for angioaccess.

This report presents our experience using double-lumen, silicone rubber, indwelling central venous catheters with a subcutaneous Dacron cuff as access for hemodialysis. Twenty-seven catheters were placed in 27 patients through venous cutdowns. A 10-cm subcutaneous tunnel was created leaving the Dacron cuff 2 cm from the external exit. Sixteen Raaf catheters (lumen diameter [LD], 1 mm), three double-lumen Hickman catheters (LD, 1.6 mm) and eight HemoCath catheters (LD, 2 mm) were used. The tip of the catheter was positioned fluoroscopically in either the superior vena cava or the right atrium. One hundred fifty-nine treatments were done with the Raaf catheters (mean blood flow [MBF], 188.1 +/- 26.4 mL/min); two of these catheters became obstructed and could not be used further. Three double-lumen Hickman catheters were used in 12 hemodialysis treatments (MBF, 216.3 +/- 27.1 mL/min). One hundred fifty-five treatments were done using the HemoCath catheters (MBF, 236.7 +/- 5.5 mL/min). The degree of recirculation of these catheters was 8.56% +/- 4.34%. The major advantages of this modality include simplicity of introduction, lack of serious complications, no sacrifice of major arteries, no need for venipuncture, and potential use in either short- or long-term hemodialysis.

Adult↗