K(+)- and temperature-evoked taurine efflux from hypothalamic astrocytes.
Hypothalamic astrocytes in culture released taurine, a suspected inhibitory amino acid neurotransmitter/neuromodulator/osmoregulator, in response to isoosmotically increasing extracellular K+ in a dose-dependent fashion. In the absence of added Ca2+, basal release levels rose to approach those obtained after exposure to 60 mM K+ in the presence of 2.5 mM Ca2+, and were only partially lowered by the addition of 10 mM Mg2+. Stimulation with K+ (60 mM) did not further increase taurine efflux above the high basal levels seen in the absence of Ca2+. Under standard conditions complete replacement of Na+ with choline Cl had little effect on basal taurine release, but reduced K(+)-evoked (60 mM) efflux by 60%. The temperature dependence of the basal levels of taurine released from hypothalamic astrocytes was similar to that seen for cultured cerebellar astrocytes and neurons over the range 5-50 degrees C. Taurine release increased from 5 to 15 degrees C, remained constant between 15 and 33 degrees C, decreased between 33 and 37 degrees C and increased thereafter. The infection point of increased basal taurine release seen around 37 degrees C (most prominent in astrocytes), may be of physiological significance. Results presented also show that the ion (Na+, Ca2+ and K+) sensitivities of taurine efflux for cultured hypothalamic astrocytes are similar to those previously reported for cultured astrocytes from the cerebellum.
Tigges
G A
GA
Department of Pharmacology, College of Medicine, University of Iowa, Iowa City 52242.
Philibert
R A
RA
Dutton
G R
GR
D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005110:Extracellular Space / Q000378:metabolism; D007031:Hypothalamus / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D013654:Taurine / Q000378:metabolism*; D013696:Temperature
D013654:Taurine; D012964:Sodium; D011188:Potassium; D002118:Calcium