SODIUM-CHANNEL MESSENGER-RNAS IN CULTURED SPINAL-CORD ASTROCYTES - IN-SITU HYBRIDIZATION IN IDENTIFIED CELL-TYPES

The expression of rat brain sodium channel a-subunit mRNAs I, II and I II and a putative glial cell-specific sodium channel (NaG) mRNA was ex amined in cultured astrocytes from P-O rat spinal cord by RNA blot hyb ridization and by non-isotope in situ hybridization cytochemistry util izing two independent sets of isoform-specific RNA probes. Sodium chan nel mRNA I was not detectable in the cultured astrocytes by RNA blot o r in situ hybridization. Sodium channel mRNA II showed negligible-to-l ow levels of expression in flat, fibroblast-like and 'pancake' astrocy tes at 4 days in vitro (div), while stellate, process-bearing astrocyt es exhibited low-to-moderate levels of mRNA II expression. At 7 div, m RNA II expression ranged from low-to-moderate in flat astrocytes and w as moderately high in most process-bearing astrocytes. In RNA blots, a weak band was observed at 9.5 kb. Sodium channel mRNA III expression was negligible in flat astrocytes and was detectable in low-to moderat e levels in stellate astrocytes beginning at 4 div; by 7 div, mRNA III was detectable in low levels in flat astrocytes and low-to-moderate l evels in stellate astrocytes. RNA blots showed two bands of nearly equ al intensity, one at 9.0 kb and one at 7.2 kb. NaG mRNA showed increas ed expression with time in culture, being detectable in flat and stell ate astrocytes at 4 div and becoming very prominent in flat astrocytes at extended times in culture. In RNA blots of cultured astrocytes at 7 div, a strong hybridizing signal with the NaG probe was observed. Th ese observations demonstrate that flat and stellate astrocytes culture d from rat spinal cord express rat brain sodium channel mRNA II and II I, and NaG, and suggest that astrocytes in vitro may co-express multip le forms of sodium channel mRNA.