Inhibition of calcium signaling in terminal and soma of carp retinal bipolar cells by GABA.
AIM
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.


CONCLUSION
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.