Biomedical subjects

A Kesthely

Publications and source records attributed to A Kesthely.

3 recordsLinked to original sources

PubMed1992

Hormone responses of in vitro bone nodule cells: studies on changes of intracellular calcium and membrane potential in response to parathyroid hormone and calcitonin.

We used two techniques to study the responses of individual in vitro bone nodule cells to parathyroid hormone (PTH) and calcitonin (CT). These techniques are laser scanning confocal imaging with a fluorescent indicator to measure intracellular free [Ca2+], and microelectrode impalement to measure the electrical potential difference across the cell membrane. We applied these measurement techniques to cells in the top cellular layer of nodules that form in vitro in cultures of cells obtained from fetal rat calvaria. Our measurements showed a transient increase in intracellular free [Ca2+] following application of PTH or CT. The duration of the increase in fluorescent intensity following PTH application varied from about 100 to more than 300 s, and the duration following CT application was from 30 to 80 s. In some measurements we applied both hormones in sequence, and observed that some cells showed an intracellular [Ca2+] response to both hormones, while other cells apparently responded to only one or the other of the hormones, or to neither. We also observed membrane potential changes in response to PTH and to CT. The membrane potential response to CT was quite small. The time courses of these membrane potential changes consisted of a depolarizing phase lasting about 100 s (with both hormones) followed by a hyperpolarizing phase (with PTH). Control measurements using only the vehicle solutions were carried out with both techniques, producing negligible responses.

Animals↗

PubMed1991

Ba(2+)-induced action potentials in osteoblastic cells.

Trains of long-duration "action potentials" were induced by Ba2+ in osteoblast-like rat osteosarcoma cells (ROS 17/2.8), under current clamp and voltage clamp. Large depolarizing pulses were seen in microelectrode measurements at 37 degrees C following the addition of 10 or 20 mM Ba2+ to physiological bathing medium. Application of BAY K 8644 resulted in the onset of the pulses at earlier times and at more negative potentials. The pulses were blocked by nifedipine and Cd2+, but not by Ni2+. Large inward current pulses were seen in whole-cell patch technique voltage-clamp measurements at 37 degrees C in the presence of from 10 to 110 mM Ba2+ in the bathing medium. The current pulses were not seen at 22 degrees C in the presence of 110 mM Ba2+, but could be induced by BAY K 8644. These pulses were not blocked by TTX, but were blocked by nifedipine, Cd2+, Zn2+, Co2+, and by an increase in bathing [Ca2+]. The shape and frequency of the current pulses were the same as for voltage pulses under current clamp. A model that can explain these observations involves opening of L-type Ca2+ channels in a voltage-independent manner by cytosolic Ba2+ via a screening of Ca2+ from sites that produce either inactivation or a lower probability of opening in the activated state. There would be a closing of these channels at higher [Ba2+] as Ba2+ is forced onto these sites. A refractory period is also required to give repeated pulses of openings.

Action Potentials↗

PubMed1991

An experimental test of a model for repeated Ca2+ spikes in osteoblastic cells.

A model for cytosolic Ca2+ spikes is presented that incorporates continual influx of Ca2+, uptake into an intracellular compartment, and Ca(2+)-induced Ca2+ release from the compartment. Two versions are used. In one, release is controlled by explicit thresholds, while in the other, release is a continuous function of cytosolic and compartmental [Ca2+]. Some model predictions are as follows. Starting with low Ca2+ influx and no spikes: (1) induction of spiking when Ca2+ influx is increased. Starting with spikes: (2) increase in magnitude and decrease in frequency when influx is reduced; (3) inhibition of spiking if influx is greatly reduced; (4) decrease in the root-mean-square value when influx is increased; and (5) elimination of spiking if influx is greatly increased. Since there is good evidence that hyperpolarizing spikes reflect cytosolic Ca2+ spikes, we used electrophysiological measurements to test the model. Each model prediction was confirmed by experiments in which Ca2+ influx was manipulated. However, the original spike activity tended to return within 5-30 min, indicating a cellular resetting process.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗