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Chloride equilibrium potential in salamander cones.
Wallace B Thoreson1, Eric J Bryson
1Department of Ophthalmology, University of Nebraska Medical Center, Omaha, NE, USA. wbthores@unmc.edu
BMC Neuroscience
|December 8, 2004
Summary
Chloride equilibrium potential (ECl) in cone terminals is near the dark resting potential. This finding suggests chloride-dependent mechanisms, like GABAa receptors, minimally impact cone neurotransmission.
Area of Science:
- Neuroscience
- Retinal Physiology
- Photoreceptor Function
Background:
- GABAergic inhibition and intracellular chloride ions influence calcium channel activity, potentially regulating photoreceptor neurotransmission.
- Chloride-dependent mechanisms are proposed to affect neurotransmitter release from cone cells.
Purpose of the Study:
- Determine the chloride equilibrium potential (ECl) in red-sensitive, large single cones from tiger salamander retinal slices.
- Assess the impact of chloride-dependent mechanisms on neurotransmitter release from cones.
Main Methods:
- Whole-cell recordings using gramicidin perforated patch techniques to preserve endogenous chloride (Cl-) levels.
- Measurement of ECl via depolarizing steps to activate calcium-activated chloride current (ICl(Ca)) and niflumic acid inhibition.
- Complementary ECl measurement using the Cl--sensitive dye MEQ and high potassium (K+) depolarization.
Main Results:
- Cone resting potentials averaged -46 mV.
- Electrophysiological recordings determined ECl to be approximately -46 mV.
- MEQ fluorescence measurements indicated ECl was below -36 mV.
Conclusions:
- The chloride equilibrium potential (ECl) in cone terminals is close to the dark resting potential.
- This proximity suggests a minimal impact of chloride-dependent presynaptic mechanisms, including GABAa receptors, glutamate transporters, and ICl(Ca), on cone terminal function.