PubMed · 5059690
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M Cherington. 1972. Long thoracic nerve. Conduction studies.. https://pubmed.ncbi.nlm.nih.gov/5059690/
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P19 embryonic carcinoma (EC) stem cells are pluripotent and are efficiently induced to differentiate into neurons and glia with retinoic acid (RA) treatment. Within 5 days, a substantial number of differentiating P19 cells express gene products that are characteristic of a neuronal phenotype. P19 neurons were used as a model to explore the relationship between neuronal "differentiation" in vitro and the acquisition of gamma-aminobutyric acid (GABAA) receptors and functional GABA responses. Pulse-labeling experiments using bromodeoxyuridine indicated that all neurons had become postmitotic within 3-4 days after treatment with RA. This was confirmed by a reduction in the immunocytochemical detection of the undifferentiated stem cell antigen SSEA-1. Subsequently, a transient expression of nestin was observed during the first 5 days in vitro (DIV) after exposure to RA. By 5-10 DIV after RA, a significant number of neurons (approximately 80-90%) expressed immunocytochemically detectable glutamate decarboxylase and GABA coincident with the acquisition of membrane binding sites for tetanus toxin. These phenotypic markers were maintained for > 30 DIV after RA. Under current-clamp conditions, random, low-amplitude, spontaneous electrical activity appeared in neurons within the first few days after RA treatment and this was blocked by the specific GABAA receptor antagonist bicuculline. Thereafter, the appearance and progressive increases in the frequency of spontaneous action potentials in P19 neurons were observed that were similarly attenuated by bicuculline. In neurons > 5 DIV after RA, exogenous application of GABA elicited similar action potentials. The onset of excitatory responses to GABA or muscimol in voltage-clamped neurons appeared immediately after the cessation of neuronal mitosis and before the previously reported acquisition of responses to glutamate. In fura-2 imaging studies, the exogenous application of GABA resulted in neuron-specific increases in intracellular Ca2+. Thus, P19 neurons provide an in vitro model for the study of the early acquisition and properties of electrical excitability to GABA and the expression of functional GABAA receptors.
BACKGROUND: Previous studies have shown that in heart there are two kinetically distinct components of delayed rectifier current: a rapidly activating component (IKr) and a more slowly activating component (IKs). The presence of IKr and/or IKs appears to be species dependent. We studied the nature of the delayed rectifier current in human ventricle in whole-cell and single-channel experiments. METHODS AND RESULTS: Ventricular myocytes were obtained from hearts of patients with ischemic or dilated cardiomyopathy. Single-channel currents and whole-cell tail currents were recorded at negative potentials directly after return from a depolarizing step. Single-channel currents were measured in the cell-attached patch configuration with 140 mmol/L K+ in the pipette. In the present study, we identified a voltage-dependent channel with a single-channel conductance of 12.9 +/- 0.8 pS (mean +/- SEM, n = 5) and a reversal potential near to the K+ equilibrium potential, suggesting that the channel is selective to K+ ions. Channel activity was observed only after a depolarizing step and increased with the duration and amplitude of the depolarization, indicating time- and voltage-dependent activation. Activation at +30 mV was complete within 300 milliseconds, and the time constant of activation, determined in the whole-cell configuration, was 101 +/- 25 milliseconds (mean +/- SEM, n = 4). The voltage dependence of activation could be described by a Boltzmann equation with a half-activation potential of -29.9 mV and a slope factor of 9.5 mV. The addition of the class III antiarrhythmic drug E-4031 completely blocked channel activity in one patch. No indications for the presence of IKs were found in these experiments. CONCLUSIONS: The conformity between the properties of IKr and those of the K+ channel in the present study strongly suggests that IKr is present in human ventricle.
Early intracellular studies of cerebral cortical neurons indicated that synaptic input evokes dendritic action potentials that convey information towards the soma. Subsequent work in vitro established that neocortical neurons produce dendritic Ca2+ action potentials. To determine whether natural stimuli elicit Ca2+ spikes, we combined the techniques of whole-cell recording, pharmacology and quantitative receptive field mapping. Our findings show that visual stimulation routinely evoked Ca2+ spikes in distinct functional and anatomical classes of cells in different layers of the cat striate cortex. Hence regenerative Ca2+ potentials appear to play a role in both the initial and later stages of cortical sensory processing.