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Voltage‐gated calcium currents in cultured embryonic Xenopus spinal neurones.
Author(s) -
Barish M E
Publication year - 1991
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1991.sp018892
Subject(s) - xenopus , biophysics , voltage dependent calcium channel , membrane potential , voltage clamp , embryonic stem cell , chemistry , electrophysiology , nifedipine , biology , calcium , neuroscience , biochemistry , organic chemistry , gene
1. Voltage‐gated Ca2+ currents were studied in cultured embryonic Xenopus spinal neurones using whole‐cell gigaohm seal techniques. Cultures of neural plate cells were established from stage 15‐17 embryos (see Methods), and were studied for up to 80 h in vitro. During this period neural precursor cells morphologically differentiate and commence expression of multiple types of voltage‐ and ligand‐gated ion channels. 2. Embryonic Xenopus neurones studied during the first 20‐40 h in culture display Ca2+ currents that correspond to the low‐voltage‐activated (T‐type) and high‐voltage‐activated forms described in other neurones and excitable cells. These Ca2+ current types could be separated based on voltage dependencies and pharmacological sensitivities. 3. T‐type Ca2+ current was activated at voltages positive to ‐50 mV, and was selectively blocked by 200 microM‐Ni2+. Curves describing the voltage dependencies of activation and steady‐state inactivation overlapped in a region centred on ‐40 mV. A small sustained Ca2+ current could be recorded within this voltage region. 4. High‐voltage‐activated (HVA) Ca2+ currents were observed at voltages positive to ‐10 mV, and could be separated into relaxing and sustained components (denoted as HVA‐relaxing and HVA‐sustained). HVA‐relaxing current was selectively reduced by Met‐enkephalin (17.5 microM). Both components of HVA current were sensitive to verapamil (100 microM), were almost completely blocked by omega‐conotoxin (3 microM) and were insensitive to nifedipine (20 microM). 5. The data indicate that T‐type Ca2+ current is present in the membrane during the initial period of channel and receptor expression, process outgrowth, and synaptogenesis, and is the dominant influence on voltage‐gated Ca2+ influx during subthreshold voltage excursions. Further, at more positive voltages, T‐type Ca2+ current contributes to inward Ca2+ current during the first 5‐10 ms after depolarizing voltage steps, and thus to inward Ca2+ current during the rising phase of the long‐lasting Ca(2+)‐dependent embryonic action potential. HVA Ca2+ currents (particularly the relaxing component) influence the plateau phase.