Voltage- and ligand-gated ion channels in floor plate neuroepithelia of the rat.
Whole-cell patch-clamp recordings were used to characterize the membrane properties and ion channel complement of floor plate neuroepithelia in embryonic and neonatal rats. The average resting potential was close to -60 mV, the capacitance was approximately 7 pS and the membrane time constant averaged 31 ms, in both neonates and embryos. Two types of K+ current were identified (i) a slowly activating, slowly inactivating current that was present in all cells, and (ii) a rapidly inactivating current that was present in 39% of cells from neonates and 64% of cells from embryos. K+ currents were significantly larger in neonates than embryos. Na+ currents were absent from all neuroepithelial cells examined. In contrast, the majority of floor plate cells exhibited a significant Ca2+ current. Biophysically this current activated at potentials positive to 60 mV and exhibited fast, voltage-dependent, inactivation. The Ca2+ current was equipermeant to Ca2+ and Ba2+, sensitive to 40-120 microM Ni2+ and only slightly inhibited by 100 microM Cd2+. These and other observations indicated this current is mediated by low-voltage-activated (i.e. T-type) Ca2+ channels. The majority of floor plate cells tested also exhibited responses to the neurotransmitter GABA which produced robust inward currents at negative membrane potentials, in chloride-loaded cells. Both the pharmacology and voltage-dependence of the GABA-activated currents indicated they arose from activation of GABA(A) receptors.
Division of Neurobiology, MRC Laboratory of Molecular Biology, Cambridge, UK.
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Frischknecht
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Randall
D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000196:embryology / Q000378:metabolism / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D004558:Electric Stimulation; D004594:Electrophysiology; D004847:Epithelial Cells / Q000187:drug effects / Q000502:physiology; D005260:Female; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism
D015220:Calcium Channels; D015221:Potassium Channels; D011963:Receptors, GABA-A