Inhibition of calcium signaling in terminal and soma of carp retinal bipolar cells by GABA.
OBJECTIVE
To investigate the effect of activation of gamma-aminobutyric acid (GABA) receptors on high K(+)-evoked Ca2+ signaling in the terminal and soma of carp retinal ON-type bipolar cells.


METHODS
Freshly dissociated carp retinal cells were loaded with fluo-3AM and then the fluorescence measurements were performed on a confocal laser-scanning microscope.


RESULTS
Ca2+ signaling evoked by high K+ 35 mmol/L was completely suppressed in both the terminal and soma of bipolar cells by GABA 100 mumol/L. However, different results were found in the terminal and soma when only one subtype of GABA receptors was activated. While activation of either GABAA or GABAC receptors totally suppressed Ca2+ signaling in the soma, a gradual elevation of [Ca2+]i appeared in the terminal. GABA 10 mumol/L could also completely suppress Ca2+ signaling in the soma, but could only partially reduce Ca2+ signaling in the terminal.


CONCLUSIONS
Activation of both GABAA and GABAC receptors could completely inhibit high K(+)-evoked Ca2+ signaling in the terminal and soma of carp retinal ON-type bipolar cells. While activation of either GABAA or GABAC receptors alone still totally suppressed Ca2+ signaling in the soma, a gradual elevation of [Ca2+]i appeared in the terminal, which may be due to desensitization of GABA receptors.
Wu
D
D
Shanghai Institute of Physiology, Chinese Academy of Sciences, Shanghai 200031, China.
Zhu
P H
PH
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002347:Carps; D002469:Cell Separation; D018079:Receptors, GABA / Q000502:physiology*; D011963:Receptors, GABA-A / Q000502:physiology*; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D015398:Signal Transduction; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
C087200:GABA-C receptor; D018079:Receptors, GABA; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D002118:Calcium