High potassium enhances secretion of neurotrophic factors from cultured astrocytes.
Elevation of extracellular potassium concentration ([K+]o) in the central nervous system (CNS), which is observed such after physiological stimuli and during ischemia, is known to be regulated by astrocytes. We suspected that in response to increased [K+]o, astrocytes might secrete some neurotrophic factor(s) to promote the survival of active and/or ischemically damaged neurons. In the present study, we examined neurotrophic activity contained in HK-ACM, i.e., astrocyte-conditioned medium (ACM) obtained after culturing astrocytes in 40 mM potassium-containing medium (HK medium). Addition of HK-ACM to basal forebrain cultures from postnatal 2-week-old (P2w) rats increased both the choline acetyltransferase (ChAT) activity (4.40-fold) and the number of ChAT-positive neurons (2.01-fold) as compared with non-conditioned HK medium. On the other hand, the neurotrophic effects of LK-ACM, i.e., ACM collected after culturing astrocytes in 4 mM potassium-containing medium (LK medium), were much weaker (2.85- and 1.41-fold for ChAT activity and number of ChAT-positive neurons, respectively) than those of HK-ACM. The neurotrophic effects of ACMs increased in a manner dependent on potassium concentration and on astrocyte culture time. Addition of an antibody against nerve growth factor (NGF) neutralized the neurotrophic effects of HK- and LK-ACMs. Direct quantification of NGF protein in ACMs by the two-site ELISA method demonstrated that a high concentration of potassium enhanced NGF secretion from cultured astrocytes. These results suggested that astrocytes secrete NGF in response to [K+]o elevation in the CNS.
Abiru
Y
Y
Division of Protein Biosynthesis, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
Katoh-Semba
R
R
Nishio
C
C
Hatanaka
H
H
D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D019208:Brain-Derived Neurotrophic Factor / Q000032:analysis / Q000378:metabolism*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D002795:Choline O-Acetyltransferase / Q000032:analysis; D002799:Cholinergic Fibers / Q000187:drug effects / Q000502:physiology; D017077:Culture Media, Conditioned / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D006624:Hippocampus / Q000166:cytology; D009414:Nerve Growth Factors / Q000032:analysis / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000201:enzymology / Q000648:ultrastructure; D011188:Potassium / Q000494:pharmacology*; D051381:Rats
D019208:Brain-Derived Neurotrophic Factor; D017077:Culture Media, Conditioned; D009414:Nerve Growth Factors; D002795:Choline O-Acetyltransferase; D011188:Potassium