Ca(2+)-dependent release of [3H]GABA in cultured chick retina cells.
Depolarization by K+ (50 mM) of cultured chick retina cells released 1.14 +/- 0.28% of the accumulated [3H] gamma-aminobutyric acid (GABA) in the absence of Ca2+, but when 1.0 mM Ca2+ was present, the internal free calcium ion concentration [Ca2+]i rose by about 750 nM and the [3H]GABA release about doubled to a value of 2.22 +/- 0.2% of the total [3H]GABA. Nitrendipine (0.1 microM), a blocker of the L-type Ca2+ channels, blocked the [Ca2+]i response to K+ depolarization by about 65%, and the omega-Conotoxin GVIA (omega-CgTx) (0.5 microM), a blocker of the N-type of Ca2+ channels, inhibited by 27% the [Ca2+]i rise due to K+ depolarization. Parallel experiments showed that nitrendipine inhibits [3H]GABA release to the level observed in the absence of Ca2+, whereas omega-CgTx did not inhibit significantly the release of [3H]GABA. The results also show that the release of [3H]GABA due to K(+)-depolarization in the absence of Ca2+ can be totally blocked by 1-(2-(((Diphenylmethylene) amino)oxy)ethyl)-1,2,5,6-tetrahydro-3-pyridine-carboxylic acid hydrochloride (NNC-711), an inhibitor of the GABA carrier. However, in the presence of Ca2+, NNC-711 blocks the release only by about 66%, corresponding to the Ca(2+)-independent release. Thus, it is concluded that [3H]GABA is released in chick retina cells by the exocytotic mechanism, which is Ca(2+)-dependent, and by reversal of the carrier, which is Ca(2+)-independent, in much the same way as has been found for other GABAergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)
Duarte
C B
CB
Center for Neurosciences of Coimbra, Department of Zoology, University of Coimbra, Portugal.
Ferreira
I L
IL
Santos
P F
PF
Oliveira
C R
CR
Carvalho
A P
AP
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D002642:Chick Embryo; D005456:Fluorescent Dyes; D007211:Indoles; D009568:Nitrendipine / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012160:Retina / Q000378:metabolism*; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D005456:Fluorescent Dyes; D007211:Indoles; D010456:Peptides, Cyclic; D014316:Tritium; D005680:gamma-Aminobutyric Acid; D020866:omega-Conotoxin GVIA; D009568:Nitrendipine; C048960:indo-1; D011188:Potassium; D002118:Calcium