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Biomedical subjects

I Chow

Publications and source records attributed to I Chow.

7 recordsLinked to original sources
PubMed1990

Cell-cell interaction during synaptogenesis.

1. Neuromuscular synapse formation was studied using nerve and muscle cells dissociated from Xenopus embryos and kept in culture for 1 to 3 days. Within a few minutes of manipulated contact with isolated cholinergic neurons, miniature endplate potential-like depolarizations (MEPPs) due to spontaneous release of acetylcholine (ACh) from the neurons were detected in the muscle cells. 2. Addition of an antibody to a frog neural cell adhesion molecule (anti-NCAM) into the culture medium of nerve-muscle co-cultured for 1-3 days decreased the percentage of functional nerve-muscle contacts. 3. Acute exposure to anti-NCAM (1 hour) inhibited significantly muscle cell contact-triggered ACh release from initially identified cholinergic neurons. 4. Lysed muscle cells manipulated into contact with neurons induced ACh release, whereas lysed neurons did not, suggesting the presence of specific molecules on the muscle cell membrane capable of triggering ACh release from the cholinergic neuron. 5. Transient appearance of electrical coupling was detected between neuronal soma and muscle cell, suggesting the possibility of exchange of modulators for the formation and maintenance of neuromuscular synapses. 6. Neuromuscular synaptogenesis constitutes a complex process where at least two different types of direct cell-cell interaction seem to occur: a) cell surface molecule contact (and binding) for cell recognition and triggering of ACh release, and b) transient intercytoplasmic communication between the cells for possible passage of modulatory molecules.

Acetylcholine↗
PubMed1988

Intercellular communication between ciliated cells in culture.

Cultured mammalian ciliated cells from the respiratory tract respond to mechanical stimulation of their cell surface by displaying a rapid transient increase in beat frequency. Surrounding adjacent and more distal neighboring ciliated cells display a similar frequency response after a short delay that is proportional to their distance from the stimulated cell. To characterize the progression of this communicated response we developed an automated computer-assisted image-analysis system to examine high-speed films of responding cells. Transmission of the frequency response between cells occurs at 0.63 cells/s at 25 degrees C and 1.54 cells/s at 37 degrees C. We have also confirmed that gap junctions exist between cells in both epithelial explants and outgrowths and that adjacent or nonadjacent ciliated, as well as nonciliated, cells are electrically coupled. We postulate that mechanical stimulation and intercellular communication provide a mechanism to regulate beat frequency between ciliated cells in order to facilitate efficient ciliary function and mucus transport.

Animals↗
PubMed1987

Quantal release of transmitter is not associated with channel opening on the neuronal membrane.

The traditional view that quantal release of neurotransmitter results from the fusion of transmitter-containing vesicles with the neuronal membrane has been recently challenged. Although various alternative mechanisms have been proposed, a common element among them is the release of cytoplasmic transmitter, which, in one view, could occur through large conductance channels on the presynaptic membrane. Six nerve-muscle cell pairs were examined with a whole-cell patch clamp for the presence of such channels that are associated with the production of miniature end-plate potentials. Examination of the neuronal membrane current during the occurrence of 822 miniature end-plate potentials produced no evidence of large channels. Thus it is unlikely that quantal release is mediated by such channels in the neuromuscular junction.

Animals↗
PubMed1987

Opening of single gap junction channels during formation of electrical coupling between embryonic muscle cells.

Gap junctions, which are low-resistance intercellular pathways, may contribute to normal embryogenesis by allowing cell-to-cell passage of as yet unidentified regulatory or inductive signals. But little is known about the properties of newly formed single junctional channels which are the basis of the communicating junctions. Reported here are the first direct measurements of current passing through single junctional channels as they form. Individual pairs of embryonic Xenopus muscle cells in culture were manipulated into contact, allowing control of the onset time and area of cellular contact, and current was recorded with the patch clamp technique. The opening of single channels which pass current between the two cells at a conductance of about 100 pS was observed within minutes of cell-cell contact. The channels opened one-at-a-time, and once formed, remained open for long periods of time, with infrequent brief closures. This suggests that formation of electrical coupling between two cells proceeds by addition of single conducting junctional channels one channel-at-a-time.

Animals↗
PubMed1985

Release of acetylcholine from embryonic neurons upon contact with muscle cell.

When a spherical muscle cell (myoball) was manipulated into contact with either the soma or the neurite of an isolated neuron in 2-day-old Xenopus nerve-muscle cultures, depolarizations similar to miniature endplate potentials (MEPPs) were frequently detected in the muscle cell. These depolarizations occurred within minutes after myoball-soma contact and within seconds after myoball-neurite contact. They had time course and amplitude distribution similar to those of the MEPPs recorded from naturally occurring neuromuscular synapses between neurites and muscle cells found in the same cultures, but they occurred at a lower frequency and had smaller average amplitudes. These depolarizations were induced by acetylcholine (ACh) since they were reversibly blocked by addition of d-tubocurarine into the culture, and they were abolished in muscle cells pretreated with alpha-bungarotoxin before contact with the neuron. Greater than 60% of the neuronal population in these cultures released ACh upon this direct muscle contact. The appearance of MEPP-like potentials in the myoball upon contact with an isolated neuron suggests that the cellular machinery responsible for ACh release is present throughout the neuron and that packages of ACh molecules are available for release prior to nerve-muscle synapse formation. We also found that neurons which had previously made synapse with other muscle cells in the culture all failed to release ACh from the soma and showed reduced release capability at the neurite for the first 30 min to 1 hr of contact with a myoball. This finding suggests that, during synapatogenesis, there is a depletion of ACh molecules and/or substances responsible for the triggering of their release in the extrasynaptic regions of the neuron.

Acetylcholine↗