Cyclic nucleotide-activated channels in carp olfactory receptor cells

Area of Science:

• Neuroscience
• Molecular Biology
• Ion Channel Physiology

Background:

• Olfactory neurons play a crucial role in detecting odors.
• Cyclic nucleotides are important second messengers in cellular signaling pathways.

Purpose of the Study:

• To investigate the effect of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) on ion permeability in carp olfactory neuron plasma membranes.
• To characterize the properties and gating mechanisms of cyclic nucleotide-dependent (CN) channels.

Main Methods:

• Utilized inside-out patch-clamp electrophysiology on carp olfactory neuron plasma membrane.
• Applied cAMP and cGMP from the cytoplasmic side to measure changes in ion permeability.
• Analyzed dose-response relationships using Hill's equation and ion selectivity using the Goldman-Hodgkin-Katz equation.

Main Results:

• cAMP and cGMP reversibly increased ion permeability, with EC50 values of 1.3 +/- 0.6 microM and 0.9 +/- 0.3 microM, respectively.
• CN-channels exhibited weak selectivity for alkali metal cations (PNa/PK/PLi/PRb/PCs = 1:0.98:0.94:0.70:0.61) and were blocked by Ca2+ and Mg2+.
• Single channel conductance was 51 +/- 9 pS in 100 mM NaCl, with maximal open probability approaching 1.0. Dichlorobenzamil reduced open probability.

Conclusions:

• Cyclic nucleotides directly modulate ion channels in carp olfactory neurons, influencing neuronal excitability.
• The characterized CN-channels possess specific ion selectivity and gating properties, suggesting a role in olfactory signal transduction.
• A four-state kinetic model (inactivated, closed, two open states) effectively describes CN-channel gating and dose-response behavior.