Stimulus-coupled taurine efflux from cerebellar neuronal cultures: on the roles of Ca++ and Na+.
Primary cultures of cerebellar neurons obtained from 7-9-day-old rats and grown 7-9 days in vitro (DIV) were used to study the effects of Na+ and Ca++ on K+-evoked taurine release. These cultures, made up largely of granule neurons (90%) and inhibitory interneurons (5-7%), produced a dose-dependent, depolarization-evoked taurine release that was Ca++-dependent at 40 mM K+, and Ca++-independent at K+ concentrations above 40 mM. The dihydropyridine Ca++ channel agonist BAY K 8644 (1 microM) augmented 30 mM K+-evoked release, while the antagonist nifedipine (5 microM) abolished both the BAY K 8644- and K+-enhanced release. Depolarization with the Na+ channel agonist veratridine (50 microM) stimulated taurine efflux, which was completely blocked by pretreatment with tetrodotoxin (2 microM). However, 50 mM K+-evoked taurine release was not affected by tetrodotoxin pretreatment. Substitution of choline Cl for NaCl partially antagonized 50 mM K+-evoked release, and by itself, the Na+ ionophore monensin (50 microM) stimulated release. These results suggest that both K+-evoked and basal taurine release from primary cerebellar neuronal cultures are sensitive to the levels of both intracellular and extracellular Na+ and Ca++. In contrast to previous findings using cerebellar astrocytes, neuronal L-type Ca++ channels, but not voltage-dependent Na+ channels, also appear to be necessary. The implications of these results on taurine's status as a putative neurotransmitter are discussed.
Philibert
R A
RA
Department of Pharmacology, College of Medicine, University of Iowa, Iowa City 52242.
Rogers
K L
KL
Dutton
G R
GR
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D002531:Cerebellum / Q000378:metabolism*; D002794:Choline / Q000494:pharmacology; D007700:Kinetics; D008985:Monensin / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000494:pharmacology*; D013654:Taurine / Q000378:metabolism*; D014701:Veratridine / Q000494:pharmacology
D013654:Taurine; D014701:Veratridine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D008985:Monensin; D012964:Sodium; D009543:Nifedipine; D002794:Choline; D002118:Calcium