Odorant receptors activated by amino acids in sensory neurons of the channel catfish Ictalurus punctatus.
Odorant receptors activated by amino acids were investigated with patch-clamp techniques in olfactory receptor neurons of the channel catfish, Ictalurus punctatus. The L-isomers of alanine, norvaline, arginine, and glutamate, known to act predominantly on different olfactory receptor sites, activated nondesensitizing inward currents with amplitudes of -2.5 to -280 pA in olfactory neurons voltage-clamped at membrane potentials of -72 or -82 mV. Different amino acids were shown to induce responses in the same sensory neurons; however, the amplitude and the kinetics of the observed whole cell currents differed among the stimuli and may therefore reflect activation of different amino acid receptor types or combinations of receptor types in these cells. Amino acid-induced currents appeared to have diverse voltage dependence and could also be classified according to the amplitude of the spontaneous channel fluctuations underlying the macroscopic currents. A mean single-channel conductance (gamma) of 360 fS was estimated from small noise whole-cell currents evoked by arginine within the same olfactory neuron in which a mean gamma value of 23.6 pS was estimated from 'large noise' response to norvaline. Quiescent olfactory neurons fired bursts of action potentials in response to either amino acid stimulation or application of 8-Br-cyclic GMP (100 microM), and voltage-gated channels underlying generation of action potentials were similar in these neurons. However, in whole-cell voltage-clamp, 8-Br-cyclic GMP evoked large rectangular current pulses, and single-channel conductances of 275, 220, and 110 pS were obtained from the discrete current levels. These results suggest that in addition to the cyclic nucleotide-gated transduction channels, olfactory neurons of the channel catfish possess a variety of odor receptors coupled to different types of transduction channels.
Ivanova
T T
TT
Department of Zoology and Physiology, Louisiana State University, Baton Rouge 70803-1725.
Caprio
J
J
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D004594:Electrophysiology; D007059:Ictaluridae / Q000378:metabolism*; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D009296:Nasal Cavity / Q000378:metabolism / Q000648:ultrastructure; D009475:Neurons, Afferent / Q000187:drug effects* / Q000648:ultrastructure; D017459:Receptors, Amino Acid / Q000187:drug effects / Q000378:metabolism; D018035:Receptors, Odorant / Q000187:drug effects* / Q000648:ultrastructure; D015398:Signal Transduction / Q000187:drug effects
D000596:Amino Acids; D017459:Receptors, Amino Acid; D018035:Receptors, Odorant; D015124:8-Bromo Cyclic Adenosine Monophosphate