Palmitate uptake by isolated, calcium-resistant cardiomyocytes was measured by using a stimulation chamber in which cell contraction can be evoked electrically. Experiments were performed in a medium containing physiological interstitial concentration of albumin (2%) and palmitate/albumin (P/A) ratios ranging from 0.03 to 2.5, and were compared to experiments with fixed P/A ratio (= 1). Initial rate of uptake (Vi) was calculated from fitted uptake vs. time curves as measured by accumulation of radioactivity in the cells from 14C-labelled palmitate. Vi-vs.-concentration curves exhibited a saturable component, if albumin concentration was kept constant. Almost no change in Vi was observed in experiments performed at constant P/A. This is in contrast to the albumin receptor hypothesis. The 14C-palmitate content of the myocytes as estimated by thin-layer-chromatography did reach a plateau at less than or equal to 30s and had the same value at 30 min after administration. The cellular content of labelled palmitate could be attributed to the membrane compartment as calculated from partition coefficient (Kc) of fatty acids (FA) between albumin and membranes. With electrical stimulation Vi-vs.-palmitate concentration kinetics showed a shift in apparent Km from 62 microM (P/A = 0.22) to 23 microM (P/A = 0.08), and presence of 2,4-dinitrophenol increases Vi. Our results suggest that FA-transfer across the sarcolemmal membranes is determined by a physicochemical equilibrium between the compartments of extracellular FA-albumin complex, the membrane lipid phase, intracellular FA binding proteins and the respective aqueous phases.(ABSTRACT TRUNCATED AT 250 WORDS)

2,4-Dinitrophenol↗

PubMedDate not supplied

Characterization of catecholamine uptake2 in isolated cardiac myocytes.

Extraneuronal catecholamine uptake was investigated in isolated quiescent rat myocardial cells. By administration of (3H-)(-)-noradrenaline concentration of 22 nmol/l up to 1000 mumol/l the following data were obtained: (1) The KM of the uptake process amounted to 260 mumol/l, the Vmax to 4.24 nmol/ (10 min x mg Protein) corresponding to 179 nmol/(min x gWWt)(WWT = Wet Weight). (2) The uptake was largely inhibited by the uptake2-inhibitors corticosterone (100 mumol/l), isoprenaline (IC50 = 30.6 mumol/l), and O-methylisoprenaline (IC50 = 2.1 mumol/l), but not by the uptake1-inhibitors cocaine (100 mumol/l) and desipramine (10 mumol/l). (3) The 'affinity'-values KM and IC50 closely agreed with those already known, but the Vmax-value was higher than those obtained in whole rat hearts by a factor of at least 1.79. This is caused presumably by the voltage dependence of the uptake mechanism and the resulting inhibition of uptake2 during the periods of depolarisation in beating hearts of other studies.

Animals↗

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Are isolated cardiomyocytes a suitable experimental model in all lines of investigation in basic cardiology?

Isolated cardiac myocytes of adult rats resemble the intact myocardium in many respects. Thus, use of isolated cells has been established in many lines of basic cardiological research. In electrophysiology, ionic channels can apparently be characterized more accurately than in intact tissue. The transport of metabolites across the sarcolemma can be studied independently of the influence of other types of cells and transport barriers. However, most reports about metabolism deal with quiescent cells, which obviously have a very low metabolic rate, provided they are intact, and their oxidative phosphorylation is not uncoupled. Thus, their application as a model of a working heart appears to be restricted. But using electrical stimulation, the metabolic activity of the cells can be gradually enhanced up to those values observed in beating hearts. In this case, the measurement of mechanical parameters as the myocytes respond to the electrical stimulation is of interest. The combination of the measurements of both metabolic and mechanical parameters in a physical model, led us to investigate the possibility of measuring inotropic effects as well as the relationship between mechanical changes and changes in oxygen consumption, e.g. as a result of the utilization of different substrates. This expands the application of the model to pharmacology, in which the influence of the mechanical action of the heart and its oxygen consumption is of major interest. If the model of isolated cardiomyocytes is employed in screening studies, a reduction in the number of experimental animals required for this line of research will inevitably result.

Animals↗

PubMedDate not supplied

A bovine model for detecting high intensity transient signals originating from mechanical heart valves.

In patients with mechanical heart valves (MHVs), transcranial Doppler methods commonly detect high intensity transient signals (HITS) representing microemboli. These microemboli, which are presumably gaseous, may cause stroke and cognitive deterioration. A bovine model was therefore developed for studying the relationship between mitral MHV induced HITS and potential etiogenic factors. We placed an 18 mm, 4 MHz Doppler probe in the brachiocephalic artery to detect MHV induced microbubbles at baseline (rest) and under 9 other conditions. To elucidate the gas composition (CO2 or N2) of the microbubbles, we administered 1%, 3%, and 5% CO2, and 100% O2. To determine effect of the heart rate, we paced the heart at 120, 160, and 180 bpm. To alter the myocardial contractility, we gave dobutamine and esmolol. Two independent, blinded observers counted the HITS from recorded doppler spectra. HITS were defined by an initial unidirectional spectral deviation, a signal power of >8 dB relative to the background power, and lack of a cyclic appearance. The electrocardiogram, aortic and LV pressures, and LV dP/dt were obtained telemetrically. The calves were studied 4 to 6, 8 to 10, and 12 to 14 weeks postoperatively, after which the animals were sacrificed at an approximate 4 month study duration, and a postmortem evaluation of the heart and the main viscera was performed. In all, 27 HITS recordings were made in 10 calves. Myocardial contractility was the only factor to significantly affect HITS frequency; the heart rate and blood gas concentrations had minimal effect on HITS frequency. Our bovine model will be useful for assessing valve designs, as well as the mechanism of HITS, the composition of the microemboli, and their possible pathophysiologic effects on the kidneys and brain.

Adrenal Glands↗

PubMedDate not supplied

Transfer of continuing education to practice: testing an evaluation model.

A continuing education (CE) program is successful only to the extent that a recommended practice or behavior is implemented. The social system in which the nurse practices and the nurse's own receptiveness to change also influence the application of new knowledge.

Attitude of Health Personnel↗

PubMedDate not supplied

MP/PIP adjustable digit blocking splint.

Explore the source record for details and available documents.

Equipment Design↗