Elsevier

Neuroscience

Volume 85, Issue 4, August 1998, Pages 1135-1149
Neuroscience

Voltage- and ligand-gated ion channels in floor plate neuroepithelia of the rat

https://doi.org/10.1016/S0306-4522(97)00641-6Get rights and content

Abstract

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 ∼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 μM Ni2+ and only slightly inhibited by 100 gM 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 GABAA receptors.

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    Present address: European Molecular Biology Laboratory, Meyerhofstrasse 1, Heidelberg, Germany.

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