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A McClellan

Publications and source records attributed to A McClellan.

11 recordsLinked to original sources
PubMed2001

High-speed solution switching using piezo-based micropositioning stages.

Motion-induced vibration is a critical limitation in high-speed micropositioning stages used to achieve solution switching. Controlled rapid solution switching is used to study the fast activation and deactivation kinetics of ligand-gated ion-channel populations isolated in excised membrane patches--such studies are needed to understand fundamental mechanisms that mediate synaptic excitation and inhibition in the central nervous system. However, as the solution-switching speed is increased, vibration induced in the piezo-based positioning stages can result in undesired, repeated, ligand application to the excised patch. The article describes a method to use knowledge of the piezo-stage's vibrational dynamics to compensate for and reduce these unwanted vibrations. The method was experimentally verified using an open-electrode technique, and fast solution switching (100 micros range) was achieved.

Models, Neurological↗
PubMed1997

Effect of hemoglobin- and Perflubron-based oxygen carriers on common clinical laboratory tests.

Polymerized hemoglobin solutions (Hb-based oxygen carriers; HBOCs) and a second-generation perfluorocarbon (PFC) emulsion (Perflubron) are in clinical trials as temporary oxygen carriers ("blood substitutes"). Plasma and serum samples from patients receiving HBOCs look markedly red, whereas those from patients receiving PFC appear to be lipemic. Because hemolysis and lipemia are well-known interferents in many assays, we examined the effects of these substances on clinical chemistry, immunoassay, therapeutic drug, and coagulation tests. HBOC concentrations up to 50 g/L caused essentially no interference for Na, K, Cl, urea, total CO2, P, uric acid, Mg, creatinine, and glucose values determined by the Hitachi 747 or Vitros 750 analyzers (or both) or for immunoassays of lidocaine, N-acetylprocainamide, procainamide, digoxin, phenytoin, quinidine, or theophylline performed on the Abbott AxSym or TDx. Gentamycin and vancomycin assays on the AxSym exhibited a significant positive and negative interference, respectively. Immunoassays for TSH on the Abbott IMx and for troponin I on the Dade Stratus were unaffected by HBOC at this concentration. Tests for total protein, albumin, LDH, AST, ALT, GGT, amylase, lipase, and cholesterol were significantly affected to various extents at different HBOC concentrations on the Hitachi 747 and Vitros 750. The CK-MB assay on the Stratus exhibited a negative interference at 5 g/L HBOC. HBOC interference in coagulation tests was method-dependent-fibrometer-based methods on the BBL Fibro System were free from interference, but optical-based methods on the MLA 1000C exhibited interferences at 20 g/L HBOC. A 1:20 dilution of the PFC-based oxygen carrier (600 g/L) caused no interference on any of these chemistry or immunoassay tests except for amylase and ammonia on the Vitros 750 and plasma iron on the Hitachi 747.

Animals↗
PubMed1994

Interference in ionized calcium measurements by heparin salts.

We determined the suitability of various heparin salts used for anticoagulation of whole-blood specimens for measurement of ionized calcium (iCa), blood gases, and electrolytes. We were particularly interested in a new heparin product containing both zinc and lithium cations (CNLZ heparin), in which the binding sites with greatest affinity for divalent cations are bound with zinc and low-affinity sites with lithium. In initial experiments Li heparin decreased iCa concentrations 0.07 mmol/L at the lowest heparin concentration (3000 units/L) and progressively lowered them at higher concentrations. Zn heparin initially increased iCa concentrations 0.06 mmol/L but progressively lowered them as the heparin concentration was increased. Li heparin interfered even when present in amounts (9 units per 3-mL syringe) minimally effective in preventing coagulation. Use of CNLZ heparin (36 units per 3-mL syringe; Zn 63-78 g/kg of heparin) largely eliminated interference of heparin in iCa measurements. In studies that included the effects of concentration of heparin through partial filling of syringes, specimens anticoagulated with CNLZ heparin compared well with unheparinized controls in measurements of iCa, blood gases, and electrolytes. Blood gases and iCa results on CNLZ-heparinized specimens from intensive-care-unit patients also compared well with specimens anticoagulated with a preparation of heparin (EB heparin) in which calcium has been added to balance the calcium-binding capacity. However, the presence of calcium in EB heparin significantly increased measured total calcium concentrations, whereas the new CNLZ heparin did not interfere in total calcium determinations.

Arteries↗
PubMed1989

Stratus automated creatine kinase-MB assay evaluated: identification and elimination of falsely increased results associated with a high-molecular-mass form of alkaline phosphatase.

We compared the performance of an automated assay of creatine kinase MB isoenzyme (CK-MB) mass (Stratus) with that of a CK-MB enzymatic assay routinely used at our institutions. Both of these assays use the same CK-MB-specific monoclonal antibody to immunocapture CK-MB, thus providing a direct means of comparing a mass assay with an activity assay. Routine CK-MB measurements for 206 samples within the analytical range of both assays revealed the following relationship: Stratus (micrograms/L) = 0.67 (activity U/L) + 0.18 (r = 0.95, Sx.y = 4.45). The linearity, sensitivity, and precision of the Stratus assay were acceptable for routine clinical use. Icteric, lipemic, and hemolyzed samples do not interfere with the assay. During our evaluation we identified a single, clinically significant false-positive sample. Because this patient had alkaline phosphatase values greater than 1100 U/L, we investigated additional samples with increased activities of alkaline phosphatase and found that samples from 12 of 23 patients selected for alkaline phosphatase values greater than 460 U/L produced falsely increased CK-MB values. We determined that a membrane-associated, high-molecular-mass form of alkaline phosphatase was a cause of these falsely increased values and instituted an approach to identify falsely increased Stratus CK-MB values. Samples from 23 of 1933 patients were falsely increased, the increase being clinically significant in samples from 14 of these patients. Consultation with the manufacturer resulted in the successful reformulation of the substrate/wash solution to minimize interferences from high-molecular-mass forms of alkaline phosphatase.

Alkaline Phosphatase↗
PubMed1988

Semi-automated direct colorimetric measurement of creatine kinase isoenzyme MB activity after extraction from serum by use of a CK-MB-specific monoclonal antibody.

This semi-automated colorimetric assay for the MB isoenzyme of creatine kinase (EC 2.7.3.2) is based on a monoclonal antibody ("Conan-MB") specific for this isoenzyme and is a modification of a previously published method (Vaidya et al., Clin Chem 1986;32:657-63). A 0.64-cm bead coated with 2 to 3 micrograms of antibody is incubated with 100 microL of serum and 10 microL of 0.2 mol/L beta-mercaptoethanol for 1 h at room temperature, to extract CK-MB. The beads are washed with de-ionized water and incubated with CK substrate for 45 min at 37 degrees C. A solution containing trans-1,2-diaminocyclohexane-N,N,N', N'-tetraacetic acid, p-iodonitrotetrazolium violet, and diaphorase is added and the resulting colored product is measured at 492 nm. The standard curve is linear to 200 U of CK-MB per liter, and analytical recovery is 97-113%. Total assay CV for low (9.7 U/L) and high (50.7 U/L) quality-control materials was 14.1% (n = 1878) and 11.6% (n = 1842), respectively. CK-MB activity correlated well (r = 0.978, n = 226) with CK-MB measured by a two-site mass immunoassay, and 99.4% of samples with CK-MB greater than or equal to 12 U/L (n = 347) were verified by electrophoresis on agarose.

Adsorption↗
PubMed1982

Mechanosensitive neurons in the spinal cord of the lamprey.

'Fictive locomotion' in the lamprey in vitro spinal cord-notochord preparation can be entrained by side to side movements of the spinal cord-notochord which mimic swimming movements even after transection of dorsal and ventral roots. This study provides direct evidence of mechanosensitive neurons intrinsic to the spinal cord. Neurons with axons located in the lateral aspect of the spinal cord discharge in response to moderate bending movements of the spinal cord. Movements of this amplitude will inevitably occur during normal swimming.

Animals↗
PubMed1981

Entrainment of the spinal pattern generators for swimming by mechano-sensitive elements in the lamprey spinal cord in vitro.

Imposed sinusoidal bending of a mobile region of the curarized spinal cord/notochord preparation of the lamprey results in phase-locking (i.e. 'entrainment') of the 'fictive swimming' motor pattern (recording in ventral roots) to the bending movements. This entrainment phenomenon occurs both with intact ventral and dorsal roots and with all roots cut (i.e. a completely isolated spinal cord). It is proposed that mechano-sensitive elements within the spinal cord contribute in part to the entrainment.

Animals↗