Extracellular potassium influences DNA and protein syntheses and glial fibrillary acidic protein expression in cultured glial cells.
Previous reports of increases in glial cell number and expression of glial fibrillary acidic protein (GFAP) in stimulated brain regions or epileptic tissue have implicated a role for increases in extracellular potassium concentration ([K+]o) in glial reactions. We examined the effects of altered [K+]o on DNA and protein syntheses and GFAP expression of cultured glial cells isolated from the posthatch chick brain stem. [K+]o was varied by adding both KCl and NaCl to K+, NaCl-free medium to achieve final [K+] of 1-50 mM. DNA and protein syntheses were measured by incorporation of 3H-thymidine and 3H-leucine, respectively, into acid-insoluble material. GFAP expression was measured by a dot-immunoblotting assay. DNA syntheses in glial cells cultured in high (5-50 mM) K+o was 45-60% less than that of cells cultured in low (1-3 mM) K+o. Protein synthesis per cell was increased 34-44% in cells cultured in high K+ as compared to those cultured in low K+. GFAP expression was inversely related to [K+]o over the 1-10 mM range. Compared to the baseline of 3 mM K+o, GFAP per cell was increased 65% at 1 mM and decreased 45% at 10 mM. These data suggest that increases in glial cell number and GFAP immunoreactivity found in sites of increased neuronal activity and in pathological tissues may not be caused solely by persistent increases in [K+]o. Instead, these results suggest that neuronal activity, through the release of K+, may have an inhibitory influence on glial proliferation and GFAP expression.(ABSTRACT TRUNCATED AT 250 WORDS)
Canady, KS; Ali-Osman, F; Rubel, EW
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