Two types of Na +‐currents in cultured rat optic nerve astrocytes: Changes with time in culture and with age of culture derivation

Publisher Website
Google Scholar
Abstract
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∞ curves. Stellate, GFAP +/A2B5 + astrocytes showed currents with h∞ 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∞ midpoints around −85 mV, almost 20 mV more hyperpolarized than in neurons or A2B5 + astrocytes. Interestingly, Na + current expression was maintained in A2B5 Na+ 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.