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K L Richards

Publications and source records attributed to K L Richards.

At least 19 recordsLinked to original sources
PubMed2000

Structure-function relationships in yeast tubulins.

A comprehensive set of clustered charged-to-alanine mutations was generated that systematically alter TUB1, the major alpha-tubulin gene of Saccharomyces cerevisiae. A variety of phenotypes were observed, including supersensitivity and resistance to the microtubule-destabilizing drug benomyl, lethality, and cold- and temperature-sensitive lethality. Many of the most benomyl-sensitive tub1 alleles were synthetically lethal in combination with tub3Delta, supporting the idea that benomyl supersensitivity is a rough measure of microtubule instability and/or insufficiency in the amount of alpha-tubulin. The systematic tub1 mutations were placed, along with the comparable set of tub2 mutations previously described, onto a model of the yeast alpha-beta-tubulin dimer based on the three-dimensional structure of bovine tubulin. The modeling revealed a potential site for binding of benomyl in the core of beta-tubulin. Residues whose mutation causes cold sensitivity were concentrated at the lateral and longitudinal interfaces between adjacent subunits. Residues that affect binding of the microtubule-binding protein Bim1p form a large patch across the exterior-facing surface of alpha-tubulin in the model. Finally, the positions of the mutations suggest that proximity to the alpha-beta interface may account for the finding of synthetic lethality of five viable tub1 alleles with the benomyl-resistant but otherwise entirely viable tub2-201 allele.

Animals↗
PubMed1999

VH4-34 encoded antibodies in systemic lupus erythematosus: a specific diagnostic marker that correlates with clinical disease characteristics.

OBJECTIVE: To determine the clinical significance of elevated serum levels of VH4-34 encoded antibodies (VH4-34 Ab) with respect to the diagnosis and clinical characteristics of systemic lupus erythematosus (SLE). METHODS: Ninety-five patients with SLE and 344 controls were studied. The controls included 34 healthy individuals, 282 patients with nonautoimmune diseases, and 28 patients with autoimmune diseases other than SLE. VH4-34 Ab levels were measured by inhibition ELISA using anti-idiotope monoclonal antibody (9G4). SLE disease activity, severity, and damage were assessed by visual analog scales, Systemic Lupus Activity Measure, Lupus Severity of Disease Index, and Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index. RESULTS: Fifty-two of 95 patients with SLE had elevated levels of VH4-34 Ab compared to 18 of 344 controls (5%), giving a sensitivity of 55% and a specificity of 95% for elevated VH4-34 Ab as a serologic test for SLE. The positive predictive value of elevated VH4-34 under these conditions was 74-85%. In this study, anti-dsDNA was not VH4-34 encoded. Significant correlations between VH4-34 and disease activity and severity indices were observed (r = 0.29-0.50). The relative risk for severe disease in SLE patients with VH4-34 antibody level in the highest tertile compared to the lowest tertile was 5.25. Twenty-five of 29 patients with lupus nephritis and 6 of 6 patients with central nervous system (CNS) lupus had elevated VH4-34 Ab. CONCLUSION: With a specificity of 94-95%, the VH4-34 antibody assay may prove valuable as a confirmatory diagnostic test for SLE. In patients with known SLE, serum VH4-34 Ab levels correlate with overall disease severity and activity, but not damage, and with nephritis and CNS lupus.

Antibodies, Antinuclear↗
PubMed1993

RPB7, one of two dissociable subunits of yeast RNA polymerase II, is essential for cell viability.

The Saccharomyces cerevisiae RNA polymerase II subunit gene RPB7 was isolated and sequenced. RPB7 is a single copy gene whose sequence predicts a 19,000 Dalton protein of 171 amino acids. RPB7 is known to dissociate from RNA polymerase II as an RPB4/RPB7 subcomplex in vitro. RPB7 also appears to interact with RNA polymerase II in a manner dependent upon RPB4, since RNA polymerase II purified from cells lacking RPB4 also lacks RPB7. Previous results have demonstrated that deletion of the RPB4 results in slow growth and cold- and temperature-sensitivity. In contrast, deletion of the RPB7 gene revealed that it is essential for cell growth and viability. Loss of both the RPB4 and the RPB7 genes causes lethality. These results suggest that RPB7 contributes to the function of RNA polymerase II in the absence of RPB4 either in a manner independent of its association with the enzyme or by directly binding to the enzyme in a manner independent of its association with RPB4.

Amino Acid Sequence↗
PubMed1991

Engineering the chloroplast genome: techniques and capabilities for chloroplast transformation in Chlamydomonas reinhardtii.

Chloroplast transformation of Chlamydomonas reinhardtii has been accomplished by agitating cell wall-deficient cells in the presence of glass beads and DNA. By using the atpB gene as the selected marker and cells grown in 0.5 mM 5-fluorodeoxyuridine, we have recovered up to 50 transformants per microgram of DNA. This method is easy and does not require specialized equipment, although it is not as efficient as the tungsten particle bombardment method [Boynton, J. E., Gillham, N. W., Harris, E. H., Hosler, J. P., Johnson, A. M., Jones, A. R., Randolph-Anderson, B. L., Robertson, D., Klein, T. M., Shark, K. B. & Sanford, J. C. (1988) Science 240, 1534-1537]. By using particle bombardment, we have developed a cotransformation approach in which spectinomycin-resistant 16S rRNA-encoding DNA is the selected marker, and we have demonstrated that cotransformation of an unselected marker on an independent replicon is very efficient. We have used this strategy (i) to recover transformants with partially deleted atpB genes that could not otherwise have been selected since they did not restore photosynthetic capability to a recipient carrying a more extensive atpB deletion and (ii) to generate specific deletion mutations in a wild-type recipient. This methodology should allow the introduction of any desired change into the chloroplast genome, even in the absence of phenotypic selection, and thus a detailed functional analysis of any chloroplast DNA sequence should be possible.

Journal Article↗
PubMed1991

Assessment of aortic and pulmonic stenosis by echocardiography.

Doppler and imaging echocardiography are highly useful methods of identifying and quantifying both aortic and pulmonic stenosis. The presence of valve stenosis and associated regurgitation is based on detecting abnormal intracardiac velocity patterns near the affected valve. Defining the specific valve involved and the type of lesion present is based on determining the location and timing of the abnormal velocities. Both color flow imaging and duplex pulsed Doppler with two-dimensional echocardiographic imaging are highly accurate in identifying the lesions present. Quantification of the severity of stenotic lesions requires calculation of the pressure gradient across the valve and estimation of valve area; quantification of volume flow rate is frequently helpful. The pressure gradient is calculated from high velocity data acquired in the stenotic valve orifice by using the Bernoulli equation. Volume flow rate through the valve can be estimated by using Doppler velocity data and two-dimensional echocardiographic imaging data acquired at sites upstream from the stenotic valve. The continuity equation allows calculation of valve area that is based on this noninvasive stroke volume and pressure gradient data. This review characterizes flow patterns present near stenotic valves, discusses the equations required to quantify aortic and pulmonic stenosis, and then describes the clinical approach to the noninvasive quantification of both stenotic lesions.

Aortic Valve Stenosis↗
PubMed1990

Accuracy of mitral Doppler echocardiographic cardiac output determinations in adults.

The Doppler echocardiographic estimation of cardiac output at the mitral valve site is often underestimated in adults with slow heart rates because the mitral valve remains open in mid-diastole when flow is markedly reduced. Therefore we tested several approaches to this measurement in 17 adults with nonvalvular heart disease who had thermodilution catheters in the right side of the heart. Superior correlations with thermal output values were obtained by a new method that excludes mitral orifice measurements during mid-diastole when flow less than 10 cm/sec (r = 0.94) compared with the standard method (r = 0.89). Also, the new method resulted in significantly less underestimation of thermal cardiac output in patients with heart rates less than 70 beats/min (-10%) compared with the standard method (-34%). In addition, use of a constant maximal two-dimensional echocardiographic mitral orifice correction factor of 0.77 with the new method to account for variations in mitral valve orifice during the cardiac cycle, as opposed to 0.68 with the standard method, resulted in similar results as compared with determining individual correction factors from M-mode echoes. We conclude that: (1) the mitral orifice approach is accurate for measuring cardiac output in adult patients with nonvalvular heart disease; (2) a new method that excludes mid-diastolic mitral orifice measurements is superior to the standard method; and (3) use of a constant two-dimensional echocardiographic mitral valve orifice correction factor obviates the need for M-mode echoes.

Cardiac Output↗
PubMed1990

Identification of an IgA inhibitor of neutrophil chemotaxis and its membrane target for the metabolic burst.

Affinity-purified IgA from the serum of an 8-year-old boy with a 5-year history of recurrent facial nodules, intermittent neutropenia and elevated immunoglobulin levels, inhibited the chemotaxis of polymorphonuclear neutrophils (PMN) from both patient and normal adults. Preincubation of normal PMN with IgA from the patient's serum (0.5 mg/ml) inhibited chemotaxis to C5a and to the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP) by 80%, while IgA or IgG from pooled human serum and IgG from the patient were without effect. Normal PMN chemotaxis was restored after IgA depletion of the patient's serum by affinity chromatography. The patient's IgA, but not IgA from pooled human serum, bound specifically to normal PMN by its antigen-binding sites and recognized a 62,000 MW membrane protein on normal neutrophils, which was distinct from the FMLP receptor, the C5a receptor, or the Fca receptor. Attachment of the patient's IgA to the 62,000 MW protein activated intracellular oxidative metabolism on a parity with phorbol myristate acetate (PMA) and resulted in a significant up-regulation of membrane receptors for FMLP. After the binding of patient (Pt) IgA, normal neutrophils were rendered significantly less responsive to subsequent stimulation with phorbol esters. These results characterize a novel mechanism of chemotactic inhibition by serum IgA and also identify a neutrophil membrane protein that is linked to intracellular oxidative metabolism.

Chemotaxis, Leukocyte↗
PubMed1988

Inadequacy of the Gorlin formula for predicting prosthetic valve area.

A total of 135 patients with normally functioning prosthetic aortic valves who were catheterized 6 months after placement of Hancock, modified Hancock or Bjork-Shiley prostheses were studied to determine the magnitude of error in Gorlin formula estimates of prosthetic aortic valve area. All patients were male, selected from 13 participating hospitals and routinely followed after valve replacement for 5 years. Hemodynamically determined Gorlin valve areas were compared with independently verified actual valve areas. Actual Hancock areas were measured from videotapes of valves exercised in a pulse duplicator flow model. Actual Bjork-Shiley areas were calculated directly from the valves' inner ring radius. Gorlin valve areas correlated poorly with actual valve areas (r = 0.39). The mean Gorlin formula error was 0.36 cm2 (standard deviation = 0.32). Gorlin areas overestimated actual areas by greater than 0.25 cm2 in 43 patients (32%) and underestimated actual areas by greater than 0.25 cm2 in 29 (21%). It was concluded that the Gorlin formula inaccurately predicts prosthetic valve area in the aortic position. Overreliance on this formula in assessing aortic stenosis could lead to errant clinical decisions.

Aortic Valve↗
PubMed1988

Differing mechanisms of exercise flow augmentation at the mitral and aortic valves.

To determine the mechanisms by which blood flow increases across the mitral and aortic valves during exercise, 18 normal men were studied during graded supine and upright bicycle exercise at matched workloads. Mitral valve orifice and ascending aortic blood velocities were recorded by Doppler echocardiography during steady states at each stage of exercise. Parasternal two-dimensional echocardiographic imaging of the ascending aorta adjacent to the aortic valve orifice and the mitral valve orifice at the tips of the valve leaflets was used to calculate changes in cross-sectional area during exercise. Heart rate increased from rest to exercise from 67 to 150 beats/min (124%) during supine exercise and from 72 to 147 beats/min (104%) during upright exercise. Stroke volume increased 20% during supine and 46% during upright exercise; the increase in stroke volume was statistically significant when rest and exercise were compared and when the magnitude of change was compared vs position (p less than .05). The increase in stroke volume measured at the ascending aorta was accomplished by an increase in the velocity-time integral (+15% supine and +48% upright, p less than .05), with little change in aortic cross-sectional area (5% supine and 0% upright, p = NS). By contrast, the increase in flow rate measured at the mitral valve was predominantly due to an increase in mean diastolic cross-sectional area (+29% supine and 34% upright, p less than .05); the velocity-time integral did not increase significantly (-10% supine and 4% upright; p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Mitral valve prolapse in patients with prior rheumatic fever.

It is known that rheumatic heart disease frequently results in isolated mitral regurgitation without concomitant mitral stenosis, especially in countries with a high prevalence of rheumatic fever. However, more recent surgical pathologic data also have demonstrated a high incidence of mitral valve prolapse in cases of rheumatic heart disease, which suggests that rheumatic fever may be a cause of mitral valve prolapse. To determine whether this association of mitral valve prolapse and rheumatic heart disease is present in a stable clinic population, we studied 30 patients who had an apical systolic murmur and a well-documented history of rheumatic fever with dynamic auscultation, two-dimensional echocardiography, and pulsed Doppler examinations. Twenty of the 30 patients (67%) had findings on physical examination consistent with isolated mitral regurgitation and 25 patients (84%) had mitral regurgitation by Doppler examination. Echocardiography demonstrated mitral valve prolapse in 24 patients (80%), whereas only one of the total study group had echocardiographic findings consistent with mitral stenosis. We conclude that (1) the presence of an isolated systolic murmur in patients with a history of rheumatic fever frequently represents pure mitral regurgitation secondary to mitral valve prolapse and (2) postinflammatory changes in valvular tissue resulting from rheumatic fever may be the etiology of mitral valve prolapse in these patients.

Adult↗
PubMed1986

Calculation of aortic valve area by Doppler echocardiography: a direct application of the continuity equation.

The continuity equation suggests that a ratio of velocities at two different cardiac valves is inversely proportional to the ratio of cross-sectional areas of the valves. To determine whether a ratio of mitral/aortic valve orifice velocities is useful in determining aortic valve area in patients with aortic stenosis, 10 control subjects and 22 patients with predominant aortic stenosis were examined by Doppler echocardiography. The ratio of (mean diastolic mitral velocity)/(mean systolic aortic velocity), (Vm)/(Va), and the ratio of (mitral diastolic velocity-time integral)/(aortic systolic velocity-time integral), (VTm)/(VTa), were determined from Doppler spectral recordings. Aortic valve area determined at catheterization by the Gorlin equation was the standard of reference. High-quality Doppler recordings were obtained in 30 of 32 subjects (94%). Catheterization documented valve areas of 0.5 to 2.6 (mean 1.1) cm2. There was good correlation between Doppler-determined (Vm)/(Va) and Gorlin valve area (r = .90, SEE = 0.23 cm2); a better correlation was noted between (VTm)/(VTa) and Gorlin valve area (r = .93, SEE = 0.18 cm2). The data demonstrate the usefulness of Doppler alone in the determination of aortic valve area in adults with absent or mild aortic or mitral regurgitation and no mitral stenosis. Although the use of mean velocity and velocity-time integral ratios requires accurate measurement of mitral and aortic velocities, it does not require squaring of these velocities or measurement of the cross-sectional area of flow.

Adult↗
PubMed1985

Doppler echocardiographic diagnosis and quantification of valvular heart disease.

Doppler echocardiography is a logical companion to ultrasound imaging in the diagnosis and quantification of valvular heart disease. Accurate noninvasive identification and quantification of valvular heart disease is now possible if both techniques are utilized together. The continued application of our knowledge of hemodynamics should extend our current uses of Doppler echocardiography to allow more intelligent management of patients with known or suspected valvular heart disease.

Blood Flow Velocity↗
PubMed1985

Comparison of Doppler echocardiographic peak frequency and turbulence parameters in the quantification of aortic stenosis in a pulsatile flow model.

To test the relative accuracy of Doppler echocardiographic peak frequency and turbulence parameters in assessing aortic stenosis, we constructed a pulsatile flow model that simulated human left ventricular and aortic pressures, flow, and anatomy. Continuous wave-measured peak frequencies and pulsed Doppler-measured turbulence were determined in the model ascending aorta for nine stenotic valve areas for each of five different flow rates. The mean squared systolic peak frequency (MSPF) and turbulence spectral envelope area (SEA) were regressed against the mean systolic gradient (r = .94, SEE = 5.6 mm Hg; and r = .96, SEE = 1.2 mm Hg, respectively). SEA was more accurate than MSPF at moderate-to-high degrees of stenosis and exhibited a smaller standard error. MSPF was more accurate than SEA in mild stenoses, where SEA tended to overestimate gradients. When flow data were included in a multiple regression analysis, both MSPF and SEA provided fair predictions of actual effective valve areas (r = .90 and r = .94, respectively). Use of high pulse-repetition-frequency Doppler echocardiography significantly reduced aliasing problems common to pulsed Doppler techniques.

Aortic Valve Stenosis↗
PubMed1985

Hydraulic estimation of stenotic orifice area: a correction of the Gorlin formula.

To determine the source of errors in the Gorlin formula for estimating stenotic valvular orifice area, we used a pulsatile flow model that emulated left ventricular and aortic pressures and flow and allowed control of ventricular outflow orifice area. After comparing orifice areas calculated by the Gorlin formula with actual orifice areas, the Gorlin formula constant (k) was found to be highly correlated with the square root of the mean transvalvular gradient (r = .95). A new formula was derived empirically and predicted areas more accurately and with smaller standard errors than the Gorlin formula in the model (r = .98, SEE = 0.11 and r = .87, SEE = 0.28, respectively) in a series of 19 patients with Hancock porcine xenograft valves (r = .89, SEE = 0.07 and r = .60, SEE = 0.12, respectively) and in the original series of patients reported by Gorlin and Gorlin in proposing the Gorlin formula (r = .93, SEE = 0.11 and r = .91, SEE = 0.12, respectively).

Aortic Valve Stenosis↗
PubMed1984

Positive inotropic and vasodilator effects of MDL 17,043 in patients with reduced left ventricular performance.

To assess the potential positive inotropic properties of the drug MDL 17,043, 10 patients were studied who had impaired left ventricular (LV) performance and who were undergoing diagnostic cardiac catheterization (LV ejection fraction 16 to 46%). MDL 17,043 was given in repeated i.v. doses of 0.5 mg/kg every 15 minutes until a maximal effect was observed or a total dose of 3 mg/kg was attained. Cardiac output increased from 3.5 +/- 1.0 to 5.3 +/- 0.7 liters/min (p less than 0.005); pulmonary artery wedge pressure decreased from 22 +/- 4 to 9 +/- 5 mm Hg (p less than 0.001); and total systemic resistance decreased from 2,335 +/- 1,147 to 1,310 +/- 365 dyne cm-5 (p less than 0.025). Also, maximal LV dP/dt increased from 1,011 +/- 301 to 1,243 +/- 330 mm Hg/s (p less than 0.001). No significant changes in heart rate, systemic blood pressure, routine blood chemistries, complete blood counts or platelet counts were observed. Thus, MDL 17,043 has hemodynamic effects consistent with positive inotropic and vasodilating properties in patients with reduced LV performance. Because this agent is effective orally, further evaluation in patients with overt congestive heart failure is warranted.

Adult↗
PubMed1984

Diastolic coronary artery pressure-flow velocity relationships in conscious man.

We characterised the diastolic pressure-flow velocity relationship in the normal left coronary artery of conscious man before and after vasodilatation with angiographic contrast medium. Phasic coronary artery pressure and flow velocity were measured in ten patients during individual diastoles (0.5 to 1.0 s) using a 20 MHz catheter-tipped, pulsed Doppler transducer. All pressure-flow velocity curves were linear over the diastolic pressure range of 110 +/- 15 (SD) mmHg to 71 +/- 7 mmHg (r = 0.97 +/- 0.01). In the basal state, values for slope and extrapolated zero flow pressure intercept averaged 0.35 +/- 0.12 cm X s-1 X mmHg-1 and 51.7 +/- 8.6 mmHg, respectively. Vasodilatation resulted in a 2.5 +/- 0.5 fold increase in mean flow velocity. The diastolic pressure-flow velocity relationship obtained during peak vasodilatation compared to that during basal conditions was characterised by a steeper slope (0.80 +/- 0.48 cm X s-1 X mmHg-1, p less than 0.001) and lower extrapolated zero flow pressure intercept (37.9 +/- 9.8 mmHg, p less than 0.05). Mean right atrial pressure for the group averaged 4.4 +/- 1.7 mmHg, while left ventricular end-diastolic pressure averaged 8.7 +/- 2.8 mmHg. These observations in man are similar to data reported in the canine coronary circulation which are consistent with a vascular waterfall model of diastolic flow regulation. In this model, coronary blood flow may be regulated by changes in diastolic zero flow pressure as well as in coronary resistance.

Adult↗