Outward Currents in Olfactory Receptor Neurons Activated by Odorants and by Elevation of Cyclic AMP

2002 ◽  
Vol 37 (1) ◽  
pp. 15-26 ◽  
Author(s):  
Raymund Y. K. Pun ◽  
Steven J. Kleene
Keyword(s):  
Cyclic Amp ◽  
Olfactory Receptor ◽  
Olfactory Receptor Neurons ◽  
Outward Currents ◽  
Receptor Neurons

Divalent cations block the cyclic nucleotide-gated channel of olfactory receptor neurons

1993 ◽  
Vol 69 (5) ◽  
pp. 1758-1768 ◽  
Author(s):  
F. Zufall ◽  
S. Firestein
Keyword(s):  
Cyclic Amp ◽  
Calcium Channels ◽  
Cyclic Nucleotide ◽  
Olfactory Receptor ◽  
Single Channel ◽  
Divalent Cations ◽  
Olfactory Receptor Neurons ◽  
Gated Channel ◽  
Receptor Neurons ◽  
Single Channel Currents

1. The effects of external divalent cations on odor-dependent, cyclic AMP-activated single-channel currents from olfactory receptor neurons of the tiger salamander (Ambystoma tigrinum) were studied in inside-out membrane patches taken from dendritic regions of freshly isolated sensory cells. 2. Channels were reversibly activated by 100 microM cyclic AMP. In the absence of divalent cations, the channel had a linear current-voltage relation giving a conductance of 45 pS. With increasing concentrations of either Ca2+ or Mg2+ in the external solution, the channel displayed a rapid flickering behavior. At higher concentrations of divalent cations, the transitions were too rapid to be fully resolved and appeared as a reduction in mean unitary single-channel current amplitude. 3. This effect was voltage dependent, and on analysis was shown to be due to an open channel block by divalent ions. In the case of Mg2+, the block increased steadily with hyperpolarization. In contrast, for Ca2+ the block first increased with hyperpolarization and then decreased with further hyperpolarization beyond -70 mV, providing evidence for Ca2+ permeation of this channel. 4. This block is similar to that seen in voltage-gated calcium channels. Additionally, the cyclic nucleotide-gated channel shows some pharmacological similarities with L-type calcium channels, including a novel block of the cyclic nucleotide channel by nifedipine (50 microM). 5. Our results indicate that the sensory generator current simultaneously depends on the presence of the second messenger and on the membrane potential of the olfactory neuron.

scholarly journals Characterization of voltage- and Ca(2+)-activated K+ channels in squid olfactory receptor neurons.

1997 ◽  
Vol 200 (11) ◽  
pp. 1571-1586
Author(s):  
M T Lucero ◽  
N Chen
Keyword(s):  
Olfactory Receptor ◽  
Cell Voltage ◽  
Olfactory Receptor Neurons ◽  
Delayed Rectifier ◽  
Outward Currents ◽  
K Current ◽  
Receptor Neurons ◽  
Q10 Values ◽  
K Currents

We performed whole-cell voltage-clamp experiments on isolated olfactory neurons from the squid Lolliguncula brevis. Total outward currents were composed of three identifiable K+ currents: a delayed rectifier K+ current that showed slow inactivation and was sensitive to 5 mmol l-1 tetraethylammonium; a rapidly inactivating, 4-aminopyridine (4-AP)-sensitive, A-type K+ current and a Ca(2+)-sensitive K+ current that was blocked by 200 nmol l-1 charybdotoxin and 10 mmol l-1 Cd2+ but was insensitive to apamin. The proportion of each current type varied from cell to cell, suggesting that responses to a given odorant would depend of the complement of channels present. The kinetics of the K+ currents were affected by temperature, with Q10 values ranging from 2 to 6. The identification and characterization of these K+ currents will greatly aid our understanding of action potential generation in these cells and will facilitate modelling of how odor responses are transduced and coded in squid olfactory receptor neurons.

Cyclic AMP Cascade Mediates the Inhibitory Odor Response of Isolated Toad Olfactory Receptor Neurons

2005 ◽  
Vol 94 (3) ◽  
pp. 1781-1788 ◽  
Author(s):  
Rodolfo Madrid ◽  
Ricardo Delgado ◽  
Juan Bacigalupo
Keyword(s):  
Cyclic Amp ◽  
Olfactory Receptor ◽  
Membrane Conductance ◽  
Receptor Potential ◽  
Olfactory Receptor Neurons ◽  
Direct Role ◽  
Olfactory Neurons ◽  
Pharmacological Agents ◽  
Receptor Neurons ◽  
20 Nm

Odor stimulation may excite or inhibit olfactory receptor neurons (ORNs). It is well established that the excitatory response involves a cyclic AMP (cAMP) transduction mechanism that activates a nonselective cationic cyclic nucleotide-gated (CNG) conductance, accompanied by the activation of a Ca2+-dependent Cl− conductance, both causing a depolarizing receptor potential. In contrast, odor inhibition is attributed to a hyperpolarizing receptor potential. It has been proposed that a Ca2+-dependent K+ (KCa) conductance plays a key role in odor inhibition, both in toad and rat isolated olfactory neurons. The mechanism underlying odor inhibition has remained elusive. We assessed its study using various pharmacological agents and caged compounds for cAMP, Ca2+, and inositol 1,4,5-triphosphate (InsP3) on isolated toad ORNs. The odor-triggered KCa current was reduced on exposing the cell either to the CNG channel blocker LY83583 (20 μM) or to the adenylyl cyclase inhibitor SQ22536 (100 μM). Photorelease of caged Ca2+ activated a Cl− current sensitive to niflumic acid (10 μM) and a K+ current blockable by charybdotoxin (20 nM) and iberiotoxin (20 nM). In contrast, photoreleased Ca2+ had no effect on cells missing their cilia, indicating that these conductances are confined to the cilia. Photorelease of cAMP induced a charybdotoxin-sensitive K+ current in intact ORNs. Photorelease of InsP3 did not increase the membrane conductance of olfactory neurons, arguing against a direct role of InsP3 in chemotransduction. We conclude that a cAMP cascade mediates the activation of the ciliary Ca2+-dependent K+ current and that the Ca2+ ions that activate the inhibitory current enter the cilia through CNG channels.

scholarly journals Voltage- and Ca(2+)-gated currents in zebrafish olfactory receptor neurons.

1996 ◽  
Vol 199 (5) ◽  
pp. 1115-1126 ◽  
Author(s):  
F S Corotto ◽  
D R Piper ◽  
N Chen ◽  
W C Michel
Keyword(s):  
Olfactory Receptor ◽  
Receptor Potential ◽  
Cell Voltage ◽  
Olfactory Receptor Neurons ◽  
Peak Amplitude ◽  
Delayed Rectifier ◽  
Maximal Conductance ◽  
Outward Currents ◽  
K Current ◽  
Receptor Neurons

Voltage- and Ca(2+)-gated currents were recorded from isolated olfactory receptor neurons (ORNs) of the zebrafish Danio rerio using the whole-cell voltage-clamp technique. Zebrafish ORNs had an average capacitance of 0.66 pF and an average apparent input resistance of 8.0 G omega. Depolarizing steps elicited transient inward currents followed by outward currents with transient and sustained components. The transient inward current (INa) was sensitive to 1 mumol l-1 tetrodotoxin, activated between -74mV and -64mV, and reached half-maximal conductance at -28 mV. Its peak amplitude averaged -101pA. Steady-state inactivation of INa was half-maximal at an average test potential of -78mV and recovery from inactivation proceeded with two time constants averaging 23 ms and 532 ms. A sustained, Co(2+)-sensitive current (ICa) activated between -44mV and -34mV and reached a peak amplitude averaging -9pA at -14mV. Outward currents were carried by K+, based on the reversal potentials of tail currents, and consisted of a Ca(2+)-dependent K+ current, a delayed rectifier current (IDR) and a transient K+ current (IA). The Ca(2+)-dependent K+ current (IK(Ca)) activated between -44mV and -34mV, whereas IDR and IA activated between -34mV and -24mV. In summary, zebrafish ORNs possess a complement of gated currents similar but not identical to that of ORNs from other vertebrates and which appears well suited for encoding a graded receptor potential into a train of action potentials.

scholarly journals An electrophysiological survey of frog olfactory cilia.

1994 ◽  
Vol 195 (1) ◽  
pp. 307-328 ◽  
Author(s):  
S J Kleene ◽  
R C Gesteland ◽  
S H Bryant
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Olfactory Receptor ◽  
Second Messengers ◽  
Olfactory Receptor Neurons ◽  
Cyclase Activity ◽  
Membrane Channels ◽  
Olfactory Cilia ◽  
Receptor Neurons ◽  
Gamma S

Individual olfactory receptor neurons vary widely in their responses to odorants. Olfactory stimulus reception occurs in the cilia of the receptor neurons. Thus, the variability among individual neurons could in part be due to differences among the olfactory cilia. We have quantified the known conductance properties of each of 117 frog olfactory cilia. From a strictly qualitative viewpoint, the cilia were very homogeneous. All but a few of them had a basal conductance in the absence of odorants and second messengers, conductances stimulated by cytoplasmic cyclic AMP and by Ca2+ and a conductance measured in the presence of ATP and stimulated by GTP gamma S. However, the magnitudes of the conductances varied widely among the cilia. Amplitudes of the cyclic-AMP- and Ca(2+)-activated ciliary currents correlated strongly with one another across the 117 cilia and 24 frogs studied, suggesting that expression of the underlying channels may be co-regulated. None of the conductance properties correlated strongly with ciliary length, a marker of cell maturity. Given cytoplasmic MgATP as substrate, ciliary adenylate cyclase apparently produced cyclic AMP, which in turn gated membrane channels and increased the ciliary conductance. In some cilia, MgATP alone caused a very large increase in conductance. In others, there was little effect unless GTP gamma S, which increases cyclase activity, was also added. No effect of cytoplasmic inositol trisphosphate on ciliary conductance was detectable.

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