Long-term treatment with ammonia affects the content and release of taurine in cultured cerebellar astrocytes and granule neurons.
High (50 mM) K+ stimulated the release of preloaded [3H]taurine from cultured cerebellar astrocytes and granule neurons with a delayed onset and only when the stimulus was applied in isoosmotic, but not in hypertonic (50 mM sucrose) medium. The process thus exhibited characteristics typical for the osmosensory or osmoregulatory response noted in a variety of nerve cell cultures. Addition of 1 mM NH4Cl to the astrocytic culture for 24 h increased the unstimulated release of [3H]taurine. However, this increase was not suppressed in a hypertonic medium, thus differing from the response accompanying regulatory volume decrease in astrocytes exposed to hypoosmolar or high potassium media. In accordance with the enhanced unstimulated release of [3H]taurine, addition of 1 mM NH4Cl decreased by 15% the taurine content in these cells. However, the addition abolished the stimulatory effect of 50 mM K+ on [3H]taurine release, indicating a loss of the osmosensory response of the cells. By contrast, treatment of granule neurons with 1 mM NH4Cl for 24 h remained without effect on any of the components of [3H]taurine release. However, the treatment increased the taurine content in granule neurons by 43%. This increase resembles the response usually noted in astrocytes adapted to hyperosmotic medium and may at least in part, reflect adaptation of the neurons to the slight increase in medium osmolarity due to the addition of ammonium chloride. The results are consistent with the selective vulnerability of astrocytes to hyperammonemic conditions, adding credence to earlier morphological observations.(ABSTRACT TRUNCATED AT 250 WORDS)
Wysmyk
U
U
Department of Biomedical Sciences, University of Tampere, Finland.
Oja
S S
SS
Saransaari
P
P
Albrecht
J
J
D000641:Ammonia / Q000633:toxicity*; D000818:Animals; D001253:Astrocytes / Q000187:drug effects*; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D013654:Taurine / Q000378:metabolism*; D013997:Time Factors
D013654:Taurine; D000641:Ammonia