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Slow changes in Ca2(+) cause prolonged release from GABAergic retinal amacrine cells
Erika D Eggers1, Justin S Klein, Johnnie M Moore-Dotson
1Department of Physiology, University of Arizona, Tucson, AZ 85724, USA. eeggers@u.arizona.edu
Journal of Neurophysiology
|May 10, 2013
Summary
Inhibitory amacrine cells in the retina release GABA slowly due to prolonged calcium buildup in their terminals, influencing visual signaling timing.
Area of Science:
- Neuroscience
- Retinal Physiology
- Synaptic Transmission
Background:
- Retinal bipolar cells use synaptic ribbons for graded glutamate release.
- Inhibitory amacrine cells modulate bipolar cell output but typically lack ribbons.
- Slow GABAergic inputs from amacrine cells influence bipolar cell output timing.
Purpose of the Study:
- To investigate the inherent release properties of GABAergic amacrine cells.
- To determine if slow GABA release is due to amacrine cell activation or intrinsic release kinetics.
- To elucidate the mechanisms underlying prolonged GABA release in the retina.
Main Methods:
- Direct electrical stimulation of amacrine cell inputs to bipolar cells.
- Measurement of GABAC receptor-mediated inhibitory currents.
- Deconvolution analysis to estimate GABA release kinetics.
- Manipulation of intracellular calcium dynamics (buffering, channel blockade).
Main Results:
- Electrically evoked GABA release showed prolonged decay, exceeding GABAC receptor kinetics.
- GABA release was inherently slow, not solely due to upstream activation.
- Transient release was observed with enhanced calcium buffering or blockade of L-type calcium channels and intracellular calcium release.
- Prolonged calcium buildup in amacrine terminals causes slow, asynchronous GABA release.
Conclusions:
- GABAergic amacrine cells exhibit slow, asynchronous release due to sustained presynaptic calcium accumulation.
- This slow release mechanism may synchronize amacrine inhibition with bipolar cell glutamate release.
- Findings reveal a novel mechanism for temporal modulation of visual information processing in the retina.
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