Different Na+ currents in P0- and P7-derived hippocampal astrocytes in vitro: evidence for a switch in Na+ channel expression in vivo.
Hippocampal astrocytes, derived from postnatal day zero (P0) rats, appear to be pluripotential with respect to sodium current expression in vitro, and display Na+ currents with h infinity midpoints close to -65 up to 5 days in vitro (DIV), and Na+ currents with midpoints close to -85 mV at 6 DIV and thereafter. These astrocytes also exhibit a biphasic pattern of Na+ current density, which is expressed at moderate levels at early times in vitro and decreases throughout the first 5 DIV, prior to expressing a second peak for the duration of time in culture. These observations have been interpreted as suggesting that astrocytes in these cultures display a 'switch' in Na+ channel biosynthesis, so that they express different types of Na+ current (with different h infinity curves) at early and later times in culture. To test the hypothesis that a similar switch in Na+ channel expression occurs in vivo, we have used patch-clamp methods to study Na+ current expression in astrocytes derived from rat hippocampus at various stages of postnatal development, P0, P4, P5 and P7. We observed a biphasic distribution of Na+ current density, which was highest in P0- and P7-derived astrocytes (18 pA/pF and 10.3 pA/pF, respectively); astrocytes derived at P4 and P5 did not express sodium currents. While P0-derived astrocytes show depolarized h infinity curves (midpoints close to -65 mV) at early times in culture, P7-derived astrocytes, studied at comparable times in vitro, display hyperpolarized h infinity curves (midpoints close to -85 mV).(ABSTRACT TRUNCATED AT 250 WORDS)
Sontheimer
H
H
Department of Neurology, Yale University School of Medicine, New Haven, CT 06510.
Ransom
B R
BR
Waxman
S G
SG
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001253:Astrocytes / Q000502:physiology*; D002478:Cells, Cultured; D006624:Hippocampus / Q000166:cytology / Q000254:growth & development*; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000502:physiology*
D015222:Sodium Channels