PubMed Health⌕ Search

Biomedical subjects

H Hendrickx

Publications and source records attributed to H Hendrickx.

At least 19 recordsLinked to original sources
PubMed1997

Evaluative learning with "subliminally" presented stimuli.

Evaluative learning refers to the change in the affective evaluation of a previously neutral stimulus (NS) that occurs after the stimulus has been associated with a second, positive or negative, affective stimulus (AS). Four experiments are reported in which the AS was presented very briefly. Significant evaluative learning was observed in participants who did not notice the presentation of the affective stimuli (ASi) (Experiment 2) or could not discriminate between the briefly presented positive and negative ASi when asked to do so (Experiment 3). In two other experiments (Experiments 1 and 4), no significant learning effect was obtained. A meta-analysis performed on the present and previously reported results (De Houwer, Baeyens, & Eelen, 1994) gave evidence for a small, though statistically reliable evaluative learning effect when ASi are presented "subliminally." This finding supports the hypothesis that evaluative associations can be learned implicitly.

Adult↗
PubMed1984

Effect of orientational order on the decay of the fluorescence anisotropy in membrane suspensions. A new approximate solution of the rotational diffusion equation.

We discussed the time-dependence of fluorescent emission anisotropy of a cylindrical probe in membrane vesicles. We showed that, if the motion of the probe were described as diffusion in an anisotropic environment, it would be possible to determine not only the second-rank but also the fourth-rank orientational order parameter from the decay of the fluorescence anisotropy. The approximations involved were based on an interpolation of short-time and long-time behavior of the relevant correlation functions. A general expression was derived for the time dependence of the fluorescence anisotropy in closed form, which applies to any particular distribution model. It was shown to be in good agreement with previously reported results for the cone model and the Gaussian model. Finally, the applicability of the theory to time-resolved and differential phase fluorescence depolarization experiments was discussed.

Diffusion↗
PubMed1984

Effect of orientational order on the decay of the fluorescence anisotropy in membrane suspensions. Experimental verification on unilamellar vesicles and lipid/alpha-lactalbumin complexes.

Various models for the analysis of time-dependent fluorescence anisotropy measurements were evaluated. The discussion was based on the analysis of pulsed experiments with 1,6-diphenyl-1,3,5-hexatriene embedded in small unilamellar vesicles of dimyristoylphosphatidylcholine or dipalmitoylphosphatidylcholine and in dimyristoylphosphatidylcholine/alpha-lactalbumin complexes. It was shown that a recently proposed model (Van der Meer, W., H. Pottel, W. Herreman, M. Ameloot, H. Hendrickx, H. Schröder, 1984, Biophys. J., 46:515-523) described the data better than did the earlier suggested cone model (Kinosita K., Jr., S. Kawato, and A. Ikegami, 1977, Biophys. J., 20:289-305). This permitted the use of the new model for the estimation of the second- and fourth-rank order parameters on nonoriented systems. The results indicated that a fraction of the probes was oriented perpendicularly to the preferred direction of the lipids. An increase of the rotational correlation times of the fluorescent probe and a higher order of its environment were detected after the interaction of alpha-lactalbumin with the dimyristoylphosphatidylcholine vesicles at acidic pH at 24.2 degrees C.

Animals↗
PubMed1983

Extension of the performance of Laplace deconvolution in the analysis of fluorescence decay curves.

The original Laplace deconvolution of luminescence data, obtained with pulsed systems, is reviewed. The system of equations from which the luminescence parameters can be determined is generalized for the case that describes the relaxation by a sum of exponentials. Artifacts such as scatter and time-shift can be taken into account. A modification of the original method that eliminates the iterative procedure in the estimation of the cut-off correction is suggested. This modified Laplace method is no longer restricted to the cases where the cut-off error is rather small and the exciting flash has a low tail. The possibility of the combination of several discrete experiments in a single Laplace deconvolution, without introducing new parameters or normalization factors, is shown. The merits of this combination method are demonstrated on a time-resolved depolarization experiment.

Luminescence↗
PubMed1975

The influence of calcium on the electrical and mechanical activity of the guinea pig ureter.

Low calcium concentration in the external medium depolarises the membrane of smooth muscle cells of the ureter and their excitability diminishes. The Ca++ dependent oscillations of the action potential disappears, while the plateau component is more resistent. Analogous reactions are observed by the addition of Ca++ antagonists such as Lantanum or Verapramil. A high Calcium concentration produces a slight hyperpolarisation, which stabilises the membrane and enhances the spike component while decreasing the plateau component of the action potential. It is possible that several drugs act indirectly on the ureter by changing the relationship between the calcium concentration of the external versus the internal medium.

Action Potentials↗
PubMed1975

The influence of potassium on the electrical and mechanical activity of the guinea pig ureter.

Increase of the external K+ concentration depolarises the ureteral muscle membrane and induces, after a transient period of increased spontaneous activity, a tonic contraction. Tetraethylammonium, in concentrations normally required for ganglion blocking activity, does not influence the ureteral activity, but in higher doses it prolonges the duration of the action potential several times and increases the intraluminal pressure. Ouabain has only an inhibitory effect on the guinea pig ureter.

Action Potentials↗
PubMed1975

The influence of sodium on the electrical and mechanical activity of the ureter.

In Sodium-deficient solutions both the electrical and mechanical activity of the ureter are reduced. The plateau component of the action potential in the smooth muscle cell of the guinea pig ureter is more affected than the oscillations. Tetrodotoxin, which blocks the action potential in nerves, does not influence activity or conduction in the ureter. This is an important argument for the myogenic conduction of activity in this tissue.

Action Potentials↗
PubMed1973

Effect of sodium and sodium-substitutes on the active ion transport and on the membrane potential of smooth muscle cells.

1. The changes of the ion content and of the membrane potential of taenia coli cells have been studied during prolonged exposure to Na-deficient solutions containing either Li or choline.2. A K-free solution containing either 71 mM-Na-71 mM-Li or 71 mM-Na-71 mM choline causes a slower loss of cellular K than a 142 mM-Na solution. In both these Na-deficient solutions the membrane hyperpolarizes to about -100 mV for periods up to 6 hr. This hyperpolarization is partially abolished by 2 x 10(-5)M ouabain.3. Replacing all extracellular Na by Li and maintaining 5.9 mM-K causes a fast loss of all Na and a progressive replacement of K by Li. These changes of the intracellular ion content are accompanied by a depolarization of the cells, suggesting that intracellular Li cannot substitute for Na in activating the ion pump.4. Exposing K-depleted cells to a K-free 71 mM-Na-71 mM-Li solution results in a ouabain sensitive transport of Na and Li against their electro-chemical gradient.5. The K-uptake by K-depleted cells from a solution containing 0.59 mM-K is increased by reducing [Na](o) to half of its normal value. This finding indicates that external Na inhibits the active Na-K exchange.6. In Na-enriched tissues half of the Na efflux is due to a ouabain insensitive Na-exchange diffusion. If Li is used as a Na substitute, the Na-Li exchange compensates for the diminution of the Na-exchange diffusion unless ouabain is added.

Animals↗
PubMed1971

Membrane potential of smooth muscle cells in K-free solution.

1. The changes of the ion content, the membrane potential and of the membrane permeability of taenia coli cells have been studied during exposure to K-free solutions. The relative value of the total membrane conductance was determined by measuring the electrotonic potential during constant current pulses with an intracellular electrode. The P(K) values were calculated from (42)K-efflux in K-free solutions.2. In solutions containing penetrating anions the cells initially depolarize. Thereafter they hyperpolarize to about - 85 mV and again depolarize after 90 min to - 5 mV. These potential changes are much smaller if large anions are used as chloride substitutes. Moreover, the final depolarization is only reached after 4-5 hr. This hyperpolarization is not inhibited by 10(-5)M ouabain.3. These potential changes are accompanied by a progressive exchange of intracellular K by Na. In solutions containing chloride or nitrate the relative value of the total membrane conductance increases to a maximal value, corresponding to the peak value of the calculated P(K). Such changes of the membrane conductance and of P(K) do not occur in K-free solutions containing large anions.4. It is proposed that the initial depolarization is probably caused by an inhibition of an electrogenic Na pump. In chloride or nitrate solution the hyperpolarization is due to an increase of the [K](i)/[K](o) ratio and to an increase of the K permeability. In the presence of large anions the hyperpolarization remains small because this increase of P(K) does not occur.

Animals↗
PubMed1971

Electrogenic sodium pump in smooth muscle cells of the guinea-pig's taenia coli.

1. The changes of the membrane potential, of the K equilibrium potential, and of the membrane conductance during K accumulation by K-depleted tissues have been studied. Three subsequent characteristic periods can be described.2. Readmission of 5.9 mM-K after complete depletion results in a rapid extrusion of Na and uptake of K, and in a rapid hyperpolarization of the cells. Initially the time course of the K equilibrium potential and the membrane potential are similar except in propionate solution. This initial period is characterized by a high membrane conductance. No change of membrane potential occurs if 10(-5)M ouabain is present.3. After 5-7 min the membrane potential becomes more negative than the K equilibrium potential. The difference between both values is larger in solutions containing propionate or in hypertonic solutions. This second phase of the recovery period is characterized by a progressive decrease of the membrane conductance.4. In a third phase both the membrane potential and the membrane resistance return to their steady-state value.5. If the external K concentration in the recovery solution is increased, the maximal hyperpolarization is less and has a shorter duration. A decrease of the temperature of the recovery solution results in a slower initial rate of repolarization and in a decrease of the maximal value of the hyperpolarization.6. These observations demonstrate the existence of an electrogenic sodium pump in smooth muscle cells during stimulation of the Na pump. An analysis of the experimental data obtained under steady-state conditions in normal Krebs solution suggests that also under these conditions an electrogenic Na pump might take part in the maintenance of the resting potential.

Animals↗