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Biomedical subjects

P Hess

Publications and source records attributed to P Hess.

139 records · Page 8Linked to original sources
PubMedDate not supplied

Prevention of deep vein thrombosis in patients with hip fractures: low molecular weight heparin versus dextran.

A randomized open trial was undertaken to compare the antithrombotic efficacy of a low molecular weight heparin (LMWH; Sandoparin) with that of dextran 70 in patients undergoing surgery for hip fracture. One hundred thirteen patients received LMWH once daily subcutaneously at a fixed dosage while 103 patients received intravenous dextran 70. Postoperative deep vein thrombosis (DVT) was assessed by a diagnostic algorithm using the 125Iodine fibrinogen uptake test as screening and Duplex ultrasonography and/or ascending venography as confirming techniques for suspected DVT. The frequency of DVT was significantly lower in the LMWH group than in the dextran group (15.5 versus 32.6%, p less than 0.005). Proximal DVT was rare in both groups (LMWH: 2%, Dextran: 1%). Only one case of fatal fat pulmonary embolism was observed during the 10 day prophylaxis period in a patient receiving Dextran. Three cases of pulmonary embolism occurred later; one fatal event in the dextran group on day 14, and two cases in the LMWH group (one fatal and one non-fatal event) on day 14 and 17, respectively. There was no major bleeding complication in either group. We conclude that the LMWH we used is safe, was well tolerated, and has a significantly better thromboprophylactic effect than dextran 70.

Adult↗
PubMedDate not supplied

Mechanism of ion permeation through calcium channels.

Calcium channels carry out vital functions in a wide variety of excitable cells but they also face special challenges. In the medium outside the channel, Ca2+ ions are vastly outnumbered by other ions. Thus, the calcium channel must be extremely selective if it is to allow Ca2+ influx rather than a general cation influx. In fact, calcium channels show a much greater selectivity for Ca2+ than sodium channels do for Na+ despite the high flux that open Ca channels can support. Relatively little is known about the mechanism of ion permeation through Ca channels. Earlier models assumed ion independence or single-ion occupancy. Here we present evidence for a novel hypothesis of ion movement through Ca channels, based on measurements of Ca channel activity at the level of single cells or single channels. Our results indicate that under physiological conditions, the channel is occupied almost continually by one or more Ca2+ ions which, by electrostatic repulsion, guard the channel against permeation by other ions. On the other hand, repulsion between Ca2+ ions allows high throughput rates and tends to prevent saturation with calcium.

Animals↗
PubMedDate not supplied

Different modes of Ca channel gating behaviour favoured by dihydropyridine Ca agonists and antagonists.

Single cardiac transmembranous Ca channels have three modes of gating behaviour in the absence of drugs, expressed as current records with brief openings (mode 1), with no openings because of channel unavailability (mode 0 or null mode) and with long-lasting openings and very brief closings that appear only rarely (mode 2). The dihydropyridine Ca agonist Bay K 8644 enhances Ca channel current by promoting mode 2, while the Ca antagonists nitrendipine and nimodipine inhibit the current by favouring mode 0.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMedDate not supplied

A novel type of cardiac calcium channel in ventricular cells.

Calcium influx is vital for several aspects of cardiac activity, so it is important to ask if heart cells possess a single or multiple types of Ca channel. Only one Ca channel type has been identified in patch-clamp studies of unitary current, despite suggestions to the contrary from whole-cell recordings in heart cells and unitary recordings from other cells. Here we describe a novel type of cardiac Ca channel with several properties that distinguish it from the hitherto-identified Ca channel in heart cells. Its conductance in isotonic Ba is small (8 pS), and is no larger in Ba than in Ca. It activates and inactivates at relatively negative potentials and remains functional long after patch excision. It is insensitive to dihydropyridines such as nimodipine and the Ca agonist Bay K 8644, and is more resistant to block by external Cd than the previously described type of cardiac Ca channel.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMedDate not supplied

Direct measurement of proton transfer rates to a group controlling the dihydropyridine-sensitive Ca2+ channel.

Protons participate in most biologically important reactions, as substrates, products, cofactors and modulators, and proton transport is an essential step in energy transduction. The dynamics of protonation reactions have been studied extensively in solution and in model systems involving lipid-water interfaces, but have never been resolved at the timescale of the elementary molecular event. Here we show that, under appropriate conditions, binding and unbinding reactions of single protons and deuterium ions to a single site on the L-type calcium channel can be resolved and the protonation and deprotonation rates quantified. The protonation rate constant considerably exceeds previous estimates obtained in simpler systems. The functional consequences of channel protonation is a threefold reduction of the channel conductance, independent of the applied voltage. The data are consistent with the presence of a single protonatable group with pK in the physiological pH range, close to the external mouth of the channel. The two conductance levels of the open channel might be explained by greatly differing local potentials associated with the protonated and deprotonated state of the group.

Animals↗
PubMedDate not supplied

Determination and confirmation of the amnesic shellfish poisoning toxin, domoic acid, in shellfish from Scotland by liquid chromatography and mass spectrometry.

During 1998 and early 1999, shellfish samples from sites in Scotland were found to contain the amnesic shellfish poisoning toxin, domoic acid (DA). Two different techniques, liquid chromatography (LC) with UV diode-array detection and LC with mass spectrometric (MS) detection, were used to detect and confirm DA in shellfish extracts. The LC/UV method was validated for routine monitoring by recovery experiments on spiked mussel and scallop tissues with a certified mussel tissue used as reference material. Crude extracts of selected samples as well as extracts cleaned with strong anion exchange (SAX) were analyzed by both LC/UV and LC/MS. Good correlation (linear regression r2 = 0.996, slope = 0.93) between the 2 methods was found for cleaned extracts. Analyses of crude extracts by LC/UV produced false-positive results in 2 crab samples, whereas LC/MS analyses gave accurate results. It was concluded that LC/UV is a valid approach for routine monitoring of DA in shellfish when cleanup is performed with a SAX cartridge to prevent false positives. A variety of shellfish species were surveyed for DA content, including Pecten maximus (king scallops), Chlamys opercularis (queen scallop), Mytilus edulis (blue mussels), Cancer pugaris (crab), and Ensis ensis (razor fish). The highest concentration of DA was 105 microg/g in Pecten maximus.

Amnesia↗
PubMedDate not supplied

Multiresidue method for determination of algal toxins in shellfish: single-laboratory validation and interlaboratory study.

A method that uses liquid chromatography with tandem mass spectrometry (LC/MS/MS) has been developed for the highly sensitive and specific determination of amnesic shellfish poisoning toxins, diarrhetic shellfish poisoning toxins, and other lipophilic algal toxins and metabolites in shellfish. The method was subjected to a full single-laboratory validation and a limited interlaboratory study. Tissue homogenates are blended with methanol-water (9 + 1), and the centrifuged extract is cleaned up with a hexane wash. LC/MS/MS (triple quadrupole) is used for quantitative analysis with reversed-phase gradient elution (acidic buffer), electrospray ionization (positive and negative ion switching), and multiple-reaction monitoring. Ester forms of dinophysis toxins are detected as the parent toxins after hydrolysis of the methanolic extract. The method is quantitative for 6 key toxins when reference standards are available: azaspiracid-1 (AZA1), domoic acid (DA), gymnodimine (GYM), okadaic acid (OA), pectenotoxin-2 (PTX2), and yessotoxin (YTX). Relative response factors are used to estimate the concentrations of other toxins: azaspiracid-2 and -3 (AZA2 and AZA3), dinophysis toxin-1 and -2 (DTX1 and DTX2), other pectenotoxins (PTX1, PTX6, and PTX11), pectenotoxin secoacid metabolites (PTX2-SA and PTX11-SA) and their 7-epimers, spirolides, and homoYTX and YTX metabolites (45-OHYTX and carboxyYTX). Validation data have been gathered for Greenshell mussel, Pacific oyster, cockle, and scallop roe via fortification and natural contamination. For the 6 key toxins at fortification levels of 0.05-0.20 mg/kg, recoveries were 71-99% and single laboratory reproducibilities, relative standard deviations (RSDs), were 10-24%. Limits of detection were <0.02 mg/kg. Extractability data were also obtained for several toxins by using successive extractions of naturally contaminated mussel samples. A preliminary interlaboratory study was conducted with a set of toxin standards and 4 mussel extracts. The data sets from 8 laboratories for the 6 key toxins plus DTX1 and DTX2 gave within-laboratories repeatability (RSD(R)) of 8-12%, except for PTX-2. Between-laboratories reproducibility (RSDR) values were compared with the Horwitz criterion and ranged from good to adequate for 7 key toxins (HorRat values of 0.8-2.0).

Animals↗
PubMedDate not supplied

The Family Connection Center: an innovative visiting program.

Child-family visiting in out-of-home care is at the heart of determining whether the family will be reunified or other permanency plans will be made. A purchase-of-service arrangement enables a voluntary agency to carry a portion of the visiting process for a public agency in a coordinated operation. A separately funded unit of the voluntary agency offers a visiting service for children of divorce whose parents are at serious odds with each other.

Child↗