ISOFORM-SPECIFIC EXPRESSION OF SODIUM-CHANNELS IN ASTROCYTES IN-VITRO- IMMUNOCYTOCHEMICAL OBSERVATIONS

The expression of sodium channel alpha-subunit isoforms in astrocytes cultured from P-0 rat spinal cord and P-7 rat optic nerve was examined utilizing immunocytochemical methods with antibodies generated agains t conserved and isoform-specific amino acid sequences of the rat brain sodium channel. In spinal cord cultures at 5 days in vitro (DIV), bot h stellate and flat astrocytes were immunostained with antibody SP20, which recognizes a conserved sequence common to sodium channel types I , II/IIA, and III. Antibody SP11-I, which is directed against a subtyp e-specific sequence in sodium channel I, did not yield detectable stai ning in spinal cord astrocytes. Antibody SP11-II, which is directed ag ainst a subtype-specific sequence in sodium channel II, immunostained both stellate and flat spinal cord astrocytes, although with less inte nsity than SP20. Antibody SP32-III, which is directed against a subtyp e-sequence in sodium channel III, immunostained stellate but not flat spinal cord astrocytes. SP20, SP11-II, and SP32-III staining persisted in stellate spinal cord astrocytes through 14-21 DIV, while SP20 and SP11-II immunostaining in flat spinal cord astrocytes was attenuated w ith time in culture. In optic nerve cultures at 5 DIV, SP20 staining w as present in both stellate and flat astrocytes, but at reduced levels compared to spinal cord astrocytes. With increased time in culture, S P20 staining was maintained in stellate optic nerve astrocytes but was gradually lost in flat optic nerve astrocytes. Stellate optic nerve a strocytes exhibited low levels of staining with SP11-I, SP11-II, and S P32-III. Flat optic nerve astrocytes lacked or displayed very low SP11 -II staining, and SP11-I and SP32-III staining was not detectable. The se observations demonstrate that cultured astrocytes are immunoreactiv e to antibodies generated against conserved and isotype-specific pepti de sequences of rat brain sodium channels, and further suggest that th ere are different patterns of sodium channel expression between flat v s. stellate astrocytes and in astrocytes derived from different region s of the CNS. (C) 1995 Wiley-Liss, Inc.