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Calcium-activated chloride conductance in frog olfactory cilia
1Department of Anatomy and Cell Biology, University of Cincinnati, Ohio 45267-0521.
Summary
Calcium ions (Ca2+) increase conductance in frog olfactory cilia. This finding suggests that odorant-induced calcium influx may alter olfactory receptor neuron function by increasing chloride permeability.
Area of Science:
- Olfactory neuroscience
- Ion channel physiology
- Cellular signaling
Background:
- Odorant detection in olfactory receptor neurons (ORNs) involves complex signaling pathways.
- The role of cytoplasmic calcium (Ca2+) in modulating ciliary function within ORNs remains incompletely understood.
- Calcium influx triggered by odorants is known to occur, but its functional consequences are unclear.
Purpose of the Study:
- To investigate the direct effects of cytoplasmic Ca2+ on the ion conductance of isolated olfactory cilia.
- To determine the relationship between Ca2+ concentration and ciliary conductance.
- To identify the ion species responsible for Ca2+-activated current and its modulation by specific inhibitors.
Main Methods:
- Excised single cilia from frog olfactory receptor neurons were used for electrophysiological measurements.
- Cytoplasmic Ca2+ levels were controlled using buffering solutions.
- Single-channel currents were recorded and analyzed to determine conductance and ion selectivity.
- The effects of a specific chloride channel inhibitor were assessed.
Main Results:
- Ciliary conductance was found to be low at 0.1 microM Ca2+ and increased significantly with higher Ca2+ concentrations.
- Maximal Ca2+-activated conductance was sevenfold higher than basal levels, with an estimated K1/2 of 5 microM, suggesting positive cooperativity.
- The Ca2+-activated current was primarily carried by chloride ions (Cl-) and was significantly inhibited (90%) by 3',5-dichlorodiphenylamine-2-carboxylate.
- Activation and deactivation kinetics of the conductance were rapid and reversible.
Conclusions:
- Cytoplasmic Ca2+ directly modulates ion channel conductance in olfactory cilia, primarily affecting chloride permeability.
- An odorant-induced Ca2+ influx into olfactory cilia is predicted to increase neuronal Cl- permeability.
- Further research is needed to determine the equilibrium potential for Cl- in ORNs to fully understand the impact on neuronal signaling.