Two types of Na(+)-currents in cultured rat optic nerve astrocytes: changes with time in culture and with age of culture derivation.
Na+ channel expression was studied in cultures of rat optic nerve astrocytes using whole-cell voltage-clamp recordings. Astrocytes from postnatal day 7 rat optic nerve (RON) expressed two distinct types of Na+ currents, which had significantly different h infinity curves. Stellate, GFAP+/A2B5+ astrocytes showed currents with h infinity curve midpoints close to -65 mV, similar to Na+ currents in most neurons. In contrast, flat fibroblast-like GFAP+/A2B5- astrocytes showed Na+ currents with h infinity midpoints around -85 mV, almost 20 mV more hyperpolarized than in neurons or A2B5+ astrocytes. Interestingly, Na+ current expression was maintained in A2B5+ astrocytes but began to decrease in A2B5- astrocytes after 6 days in vitro (DIV) and fell to or below the level of detection (i.e., 1 pA/pF) at 12 DIV. Astrocytes cultured from neonatal rats (P0) are almost exclusively GFAP+/A2B5-. These cells did not display measurable Na+ currents when studied at 2 DIV; however, Na+ current was observed after 5 DIV in A2B5- astrocytes from these neonatal (P0) cultures. These findings were substantiated by immunocytochemical experiments using 7493, an antibody raised against purified rat brain Na+ channels; in P0-derived astrocyte cultures 7493 antibody staining was initially lacking (up to 3 DIV), but it was prominent in cultures after 5 DIV, suggesting that Na+ current expression in RON astrocytes occurs postnatally.
Sontheimer
H
H
Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510.
Minturn
J E
JE
Black
J A
JA
Ransom
B R
BR
Waxman
S G
SG
D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000502:physiology; D004396:Coloring Agents; D004594:Electrophysiology; D005904:Glial Fibrillary Acidic Protein / Q000494:pharmacology; D007150:Immunohistochemistry; D009900:Optic Nerve / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D015222:Sodium Channels / Q000378:metabolism*; D013997:Time Factors
D004396:Coloring Agents; D005904:Glial Fibrillary Acidic Protein; D015222:Sodium Channels