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H A Schultens

Publications and source records attributed to H A Schultens.

8 recordsLinked to original sources
PubMed1999

Small conductance potassium channels cause an activity-dependent spike frequency adaptation and make the transfer function of neurons logarithmic.

We made a computational model of a single neuron to study the effect of the small conductance (SK) Ca2+-dependent K+ channel on spike frequency adaptation. The model neuron comprised a Na+ conductance, a Ca2+ conductance, and two Ca2+-independent K+ conductances, as well as a small and a large (BK) Ca2+-activated K+ conductance, a Ca2+ pump, and mechanisms for Ca2+ buffering and diffusion. Sustained current injection that simulated synaptic input resulted in a train of action potentials (APs) which in the absence of the SK conductance showed very little adaptation with time. The transfer function of the neuron was nearly linear, i.e., both asymptotic spike rate as well as the intracellular free Ca2+ concentration ([Ca2+]i) were approximately linear functions of the input current. Adding an SK conductance with a steep nonlinear dependence on [Ca2+]i (. Pflügers Arch. 422:223-232; Köhler, Hirschberg, Bond, Kinzie, Marrion, Maylie, and Adelman. 1996. Science. 273:1709-1714) caused a marked time-dependent spike frequency adaptation and changed the transfer function of the neuron from linear to logarithmic. Moreover, the input range the neuron responded to with regular spiking increased by a factor of 2.2. These results can be explained by a shunt of the cell resistance caused by the activation of the SK conductance. It might turn out that the logarithmic relationships between the stimuli of some modalities (e.g., sound or light) and the perception of the stimulus intensity (Fechner's law) have a cellular basis in the involvement of SK conductances in the processing of these stimuli.

Action Potentials↗
PubMed1994

Localization of calcium entry through calcium channels in olfactory receptor neurones using a laser scanning microscope and the calcium indicator dyes Fluo-3 and Fura-Red.

The intracellular calcium concentration [Ca2+]i in olfactory receptor neurones of Xenopus laevis was imaged with high spatial and temporal resolution. A new method using a mixture of the calcium indicator dyes Fluo-3 and Fura-Red was employed. The fluorescence patterns in two wavelength bands were measured on the emission side of a confocal laser scanning microscope, and the ratio R of the fluorescence intensities was taken as an estimate of [Ca2+]i. When the neurones were depolarized by elevating the extracellular potassium concentration [K+]o they showed one of three types of responses: a fast increase in [Ca2+]i, a slow increase in [Ca2+]i, or no change in [Ca2+]i. The fast increase in [Ca2+]i took place in the soma compartment. For at least 4 s after the onset of depolarization the calcium distribution in the dendrite remained essentially unchanged. To study the fast increase with high time resolution, line scan images were taken. The neurones were depolarized for brief periods applying a solution containing high [K+] onto the soma from an application pipette. The fast increase in [Ca2+]i began with a delay of about 200 ms and went from the resting concentration to about 110 nM above resting concentration. Following the depolarization, recovery from elevated [Ca2+]i to resting levels had a time constant of about 15 s. The slow response seemed to depend on the removal of [Na+] from the bath rather than on the elevated [K+] in the bath. The response was also observed with Cd2+, Ni2+, and Co2+ (1.5 mM each) in the bath.(ABSTRACT TRUNCATED AT 250 WORDS)

Aniline Compounds↗
PubMed1982

Measures of transinformation for multiple input/single output neuronal systems.

This paper presents a method for the calculation of the information transfer, or transinformation, in multiple input/single output neuronal systems. Our approach is an extension of an approach introduced by Eckhorn and Poepel in 1974. These authors computed the transinformation in single input/single output neuronal channels by regarding the spike (or stimulus) trains involved as finite Markov chains. The expressions for multiple input systems presented here are derived in close analogy to formulae in linear systems theory which show explicitly the correlations between the different input channels. A number of equivalent forms for the transinformation are discussed.

Animals↗
PubMed1977

Correlation of physical and morphological parameters with release of catecholamines, ATP, and protein from adrenal medulla chromaffin granules.

Exchanging 0.3 M sucrose for 0.3 M glycerol as the bathing medium for isolated bovine adrenal chromaffin granules at 0 degrees C or raising the temperature of granules suspended in 0.3 M sucrose to 37 degrees C causes the release of catecholamines, ATP and soluble protein stored in the granules. These treatments also reduce the turbidity (absorbance at a non-absorbing wavelength) of the same suspensions. The glycerol-induced release is shown by morphology and morphometry to be due to lysis of the granules. Advantage is taken of the difference in density of the intact granules and the granule ghosts to confirm this result by centrifugation of glycerol-incubated samples on continuous gradients of sucrose and metrizamide. Similar centrifugation experiments performed on the granules incubated in sucrose at 37 degrees C show that lysis also accounts for the fast phase of release of granule contents, and not graded selective release of material from otherwise intact granules.

Adenosine Triphosphate↗
PubMed1977

An osmometer model for changes in the buoyant density of chromaffin granules.

We present a model for the structure of isolated bovine adrenal medulla chromaffin granules derived from the dependence of granule density on the osmotic pressure of the suspension medium at 2 degrees C. The granule consists of a flexible, inelastic membrane bounding an osmotically active core. The core consists of a solution space and a separate, nonosmotic phase. Since the granule behaves like a "perfect" osmometer over a wide range of osmolarities, we conclude that (a) within these limits, the core consists of a constant amount of condensed material and a constant number of particles in solution, (b) from the constraints of the osmometer model, the osmolality inside the granule must equal the osmolality outside. Therefore the high concentrations of catecholamines (greater than 0.7 M) and ATP (greater than 0.18 M) measured biochemically cannot be dissolved in the core solution as separate molecules, but must be condensed into larger aggregates. These results are supported by electron micrographic examination of the effect of osmotic pressure changes on granule morphology.

Adenosine Triphosphate↗