A simple electronic device for time-lapse recording of neural and other cell movements using a home video cassette recorder

This article describes a simple electronic unit to obtain time-lapse recordings with the use of a common remote-controlled home video cassette recorder, for example a VHS recorder. The electronic unit is a timer to be connected to the remote-control unit. The video cassette recorder itself remains unchanged. Replay of the recorded images speeds up the original process by a factor of 2-100 × or more. This technique has been applied in video micrographic studies of (1) the development of dorsal root ganglion (DRG) cells in culture, including growth cone and Schwann cell movements, and (2) tumor cell killing by natural killer (NK) cells

Self-restoration of cardiac excitation rhythm by anti-arrhythmic ion channel gating

Homeostatic regulation protects organisms against hazardous physiological changes. However, such regulation is limited in certain organs and associated biological processes. For example, the heart fails to self-restore its normal electrical activity once disturbed, as with sustained arrhythmias. Here we present proof-of-concept of a biological self-restoring system that allows automatic detection and correction of such abnormal excitation rhythms. For the heart, its realization involves the integration of ion channels with newly designed gating properties into cardiomyocytes. This allows cardiac tissue to i) discriminate between normal rhythm and arrhythmia based on frequency-dependent gating and ii) generate an ionic current for termination of the detected arrhythmia. We show in silico, that for both human atrial and ventricular arrhythmias, activation of these channels leads to rapid and repeated restoration of normal excitation rhythm. Experimental validation is provided by injecting the designed channel current for arrhythmia termination in human atrial myocytes using dynamic clamp

Theoretical analysis of human muscle membrane behaviour in hypokalemic periodic paralysis

Computer simulations were performed to investigate the behavior of human muscle membrane with membrane defects supposed to be present in the muscular disease Hypokalemic Periodic Paralysis (HOPP). The model used for simulation was a Hodgkin-Huxley model. The T-tubular system was also incorporated. It was studied whether the membrane defects caused the following recorded HOPP phenomena: a slight depolarization of a HOPP muscle cell when serum potassium is normal and a strong depolarization to -50 mV when serum potassium is low. In the authors' model a constant small sodium leak conductance slightly depolarized the cell, whereas a small fraction of noninactivating sodium channels caused a strong depolarization. In the case of a dependency of this fraction on serum potassium according to a Boltzmann relation such a depolarization occurred only when serum potassium was low. In the authors' simulations, the resting membrane potential moved from -90 mV to -30 mV after a single action potential when 8%, or more of the sodium channels did not inactivate. The authors' results were qualitatively similar when the T-tubular system was decouple

Identification of Ca2+‐activated K+ channels in cells of embryonic chick osteoblast cultures

Primary cultures of embryonic chick osteoblasts consist of a heterogeneous cell population. Patch clamp measurements were done on 1‐ to 5‐day‐old osteoblasts, osteocytes, fibroblastlike cells, and cells that could not be classified on morphologic criteria. The measurements showed the omnipresence of depolarization‐activated high‐conductance channels in cell‐attached patches. The whole‐cell experiments showed an outward rectifying conductance activating at positive membrane potentials. Channels underlying the latter conductance were found to be K+ conducting in outside‐out membrane patches. The activation potential of the outward rectifying K+ conductance shifted to negative membrane potentials upon increasing the intracellular Ca2+ concentration within the range of 10−8–10−3.2 M. The same happened with the activation potential of the K+ channels found in outside‐out patches. Finally, inside‐out patch experiments directly demonstrated the dependency of the activation potential of K+ channels on Ca2+ ions. Thus the identity and main characteristics of Ca2+‐activated K+ channels expressed by the various cell types present in chick osteoblast cultures have now been established. Decreased input resistances were found in cells of cultures more than 2 days old. This is consistent with the establishment of electrical coupling between the cells. Functions in which Ca2+‐activated K+ channels could play a role are discussed

High‐conductance anion channels in embryonic chick osteogenic cells

Patch‐clamp measurements done on excised membrane patches obtained from 1‐5 day cultured embryonic chick osteoblasts, osteocytes, and periosteal fibroblasts revealed the existence of a high‐conductance anion channel: 371 ± 63 pS when measured under symmetrical 158 mM CI− conditions. The channel frequently displayed subconductance levels. The ion selectivity of the channel expressed as the (an)ion to chloride permeability ratio was as follows: CI− (1.0) > methylsulfate− (0.71) > gluconate− (0.25) > glutamate− (0.17) > Na+ = K+ (0.10). In addition, the channel had a significant permeability for inorganic phosphate ions. The channel was found in about 1% of the cell‐attached patches, which indicates that the channel is under the control of as yet unknown intracellular factors. Once activated by patch excision, the channel was voltage dependent and active at potentials close to 0 mV. At potentials outside the range of ± 10 mV channel activity decreased. This process proceeded faster at increasing membrane potentials of either polarity. Returning to potentials close to 0 mV caused reopening of the channels within seconds if the preceding voltage step led to complete closure of the channels. Channel activity did not depend noticeably on intracellular and extracellular Ca2+ ions. The channel is not unique to (chick) osteogenic cells but has been demonstrated in excised patches obtained from excitable and other nonexcitable cells. Although its presence in a wide variety of cell types suggests that the channel plays a general role in as yet unknown cell physiologic processes, the channel may also have specific functions in osteogenic cells, for example providing a pathway for phosphate ions during mineralization

A Ca2+-dependent K+-channel in freshly isolated and cultured chick osteoclasts

Calcium-activated potassium channels were found in embryonic chick osteoclasts using the patch-clamp technique. The activity of the channel was increased by both membrane depolarisation and an increase in intracellular Ca2+ concentration in the range 10-5 to 10-3 M. In the cell-attached-patch configuration the channel was only active at extreme depolarising potentials. Ca2+ addition to the cytoplasm via ionomycin increased channel activity at the resting membrane potential of the osteoclast. The channel had a single-channel conductance of 150 pS in the inside-out patch under symmetrical K+ conditions (150 mM) and was selective for potassium ions. During sustained application of increased [Ca2+] at the cytoplasmic side of inside-out patches, channel activity sometimes decreased again after the initial increase (desensitization). The results established the properties of the single channels underlying an outward rectifying K+ conductance in chick osteoclasts described previously by us