Potentiometric study of resting potential, contributing K+ channels and the onset of Na+ channel excitability in embryonic rat cortical cells.
Resting membrane potential (RMP), K+ channel contribution to RMP and the development of excitability were investigated in the entire population of acutely dissociated embryonic (E) rat cortical cells over E11-22 using a voltage-sensitive fluorescent indicator dye and flow cytometry. During the period of intense proliferation (E11-13), two cell subpopulations with distinct estimated RMPs were recorded: one polarized at approximately -70 mV and the other relatively less-polarized at approximately -40 mV. Ca2+o was critical in sustaining the RMP of the majority of less-polarized cells, while the well-polarized cells were characterized by membrane potentials exhibiting a approximately Nernstian relationship between RMP and [K+]o. Analysis of these two subpopulations revealed that > 80% of less-polarized cells were proliferative, while > 90% of well-polarized cells were postmitotic. Throughout embryonic development, the disappearance of Ca2+o-sensitive, less-polarized cells correlated with the disappearance of the proliferating population, while the appearance of the K+o-sensitive, well-polarized population correlated with the appearance of terminally postmitotic neurons, immuno-identified as BrdU-, tetanus toxin+ cells. Differentiating neurons were estimated to contain increased K+i relative to less-polarized cells, coinciding with the developmental expression of Cs+/Ba2+-sensitive and Ca2+-dependent K+ channels. Both K+ channels contributed to the RMP of well-polarized cells, which became more negative toward the end of neurogenesis. Depolarizing effects of veratridine, first observed at E11, progressively changed from Ca2+o-dependent and tetrodotoxin-insensitive to Na+o-dependent and tetrodotoxin-sensitive response by E18. The results reveal a dynamic development of RMP, contributing K+ channels and voltage-dependent Na+ channels in the developing cortex as it transforms from proliferative to primarily differentiating tissue.
Maric
D
D
Laboratory of Neurophysiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA. dragan@codon.nih.gov
Maric
I
I
Smith
S V
SV
Serafini
R
R
Hu
Q
Q
Barker
J L
JL
D000818:Animals; D001464:Barium / Q000494:pharmacology; D001973:Bromodeoxyuridine / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002455:Cell Division; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000187:drug effects / Q000196:embryology / Q000502:physiology*; D002586:Cesium / Q000494:pharmacology; D004622:Embryo, Mammalian; D005434:Flow Cytometry; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D062687:Sodium Channel Agonists; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D014701:Veratridine / Q000494:pharmacology
D015221:Potassium Channels; D062687:Sodium Channel Agonists; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D002586:Cesium; D001464:Barium; D013779:Tetrodotoxin; D014701:Veratridine; D001973:Bromodeoxyuridine; D011188:Potassium; D002118:Calcium