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Polyamines and Ca 2+ Mediate Hyperosmolal Opening of the Blood‐Brain Barrier: In Vitro Studies in Isolated Rat Cerebral Capillaries
Author(s) -
Koenig Harold,
Goldstone Alfred D.,
Lu Chung Y.,
Trout Jerome J.
Publication year - 1989
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1989.tb01858.x
Subject(s) - putrescine , spermidine , mannitol , ornithine decarboxylase , stimulation , polyamine , blood–brain barrier , chemistry , biochemistry , endocrinology , medicine , biology , enzyme , central nervous system
We recently presented evidence that the reversible opening of the blood‐brain barrier (BBB) by the infusion of 1.6 M mannitol into the rat internal carotid artery is mediated by a rapid stimulation of ornithine decarboxylase (ODC) activity and putrescine synthesis in cerebral capillaries. We have now investigated this hypothesis further, using isolated rat cerebral capillaries as an in vitro model of the BBB. The ODC activity of cerebral capillary preparations was enriched up to 15‐fold over that of the cerebral homogenate. Hyperosmolal mannitol in physiological buffer evoked a rapid (<15 s), concentration‐ and time‐dependent increase in capillary ODC activity and an accumulation of putrescine and spermidine which was blocked by the specific ODC inhibitor, α‐ difluoromethylornithine (DFMO, 10 m M ). Mannitol (1 M ), as well as 2 M urea, evoked a two‐ to fivefold increase in the temperature‐sensitive influx of 45 Ca 2+ and uptake of horseradish peroxidase (HRP) and 2‐deoxy‐D‐[1‐ 3 H]glucose (DG), but not α‐[1‐ 14 C]aminoisobutyrate, during a 2‐min incubation. DFMO (10 m M ) abolished 1 M mannitol‐mediated stimulation of 45 Ca 2+ influx and uptake of HRP and DG, whereas 1 m M putrescine replenished capillary polyamines and reversed the DFMO effects. Mannitol (1 M )‐induced stimulation of ODC activity and membrane transport processes was Ca 2+ ‐dependent and verapamil‐ and nisoldipine‐sensitive. Phorbol myristate acetate (PMA, 10 n M ), a protein kinase C activator, also evoked a two‐ to threefold stimulation of 45 Ca 2+ transport and HRP and DG uptake. This PMA effect was abolished by DFMO, suggesting involvement of rapid, ODC‐controlled polyamine synthesis. The effects of 10 n M PMA and 1 M mannitol were additive, suggesting that hyperosmolal stimulation of ODC‐activated polyamine synthesis does not involve protein kinase C. These data support the hypothesis that ODC‐activated polyamine synthesis and Ca 2+ influx (via Ca 2+ channels) play a key role in mediating the effects of hyperosmolality on BBB permeability.