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

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.

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

Journal of Experimental Biology ◽

10.1242/jeb.199.5.1115 ◽

1996 ◽

Vol 199 (5) ◽

pp. 1115-1126 ◽

Cited By ~ 1

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.

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Voltage-dependent and odorant-regulated currents in isolated olfactory receptor neurons of the channel catfish.

The Journal of General Physiology ◽

10.1085/jgp.99.4.505 ◽

1992 ◽

Vol 99 (4) ◽

pp. 505-529 ◽

Cited By ~ 37

Author(s):

T Miyamoto ◽

D Restrepo ◽

J H Teeter

Keyword(s):

Action Potentials ◽

Olfactory Receptor Neurons ◽

Olfactory Neurons ◽

Outward Currents ◽

Na Currents ◽

Voltage Dependent ◽

Inward Currents ◽

K Current ◽

Receptor Neurons ◽

K Currents

The electrical properties of olfactory receptor neurons, enzymatically dissociated from the channel catfish (Ictalurus punctatus), were studied using the whole-cell patch-clamp technique. Six voltage-dependent ionic currents were isolated. Transient inward currents (0.1-1.7 nA) were observed in response to depolarizing voltage steps from a holding potential of -80 mV in all neurons examined. They activated between -70 and -50 mV and were blocked by addition of 1 microM tetrodotoxin (TTX) to the bath or by replacing Na+ in the bath with N-methyl-D-glucamine and were classified as Na+ currents. Sustained inward currents, observed in most neurons examined when Na+ inward currents were blocked with TTX and outward currents were blocked by replacing K+ in the pipette solution with Cs+ and by addition of 10 mM Ba2+ to the bath, activated between -40 and -30 mV, reached a peak at 0 mV, and were blocked by 5 microM nimodipine. These currents were classified as L-type Ca2+ currents. Large, slowly activating outward currents that were blocked by simultaneous replacement of K+ in the pipette with Cs+ and addition of Ba2+ to the bath were observed in all olfactory neurons examined. The outward K+ currents activated over approximately the same range as the Na+ currents (-60 to -50 mV), but the Na+ currents were larger at the normal resting potential of the neurons (-45 +/- 11 mV, mean +/- SD, n = 52). Four different types of K+ currents could be differentiated: a Ca(2+)-activated K+ current, a transient K+ current, a delayed rectifier K+ current, and an inward rectifier K+ current. Spontaneous action potentials of varying amplitude were sometimes observed in the cell-attached recording configuration. Action potentials were not observed in whole-cell recordings with normal internal solution (K+ = 100 mM) in the pipette, but frequently appeared when K+ was reduced to 85 mM. These observations suggest that the membrane potential and action potential amplitude of catfish olfactory neurons are significantly affected by the activity of single channels due to the high input resistance (6.6 +/- 5.2 G omega, n = 20) and low membrane capacitance (2.1 +/- 1.1 pF, n = 46) of the cells.(ABSTRACT TRUNCATED AT 400 WORDS)

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Electrophysiological characterization of rat and mouse olfactory receptor neurons from an intact epithelial preparation

Journal of Neuroscience Methods ◽

10.1016/s0165-0270(99)00089-8 ◽

1999 ◽

Vol 92 (1-2) ◽

pp. 31-40 ◽

Cited By ~ 50

Author(s):

Minghong Ma ◽

Wei R Chen ◽

Gordon M Shepherd

Keyword(s):

Olfactory Receptor ◽

Olfactory Receptor Neurons ◽

Receptor Neurons ◽

Electrophysiological Characterization

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Characterization of Calcium-activated Chloride Channels in Patches Excised from the Dendritic Knob of Mammalian Olfactory Receptor Neurons

The Journal of Membrane Biology ◽

10.1007/s002329900323 ◽

1998 ◽

Vol 161 (2) ◽

pp. 163-171 ◽

Cited By ~ 40

Author(s):

M. Hallani ◽

J.W. Lynch †, ‡ , P.H. Barry

Keyword(s):

Olfactory Receptor ◽

Chloride Channels ◽

Olfactory Receptor Neurons ◽

Receptor Neurons

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Odor sensitivity of cultured lobster olfactory receptor neurons is not dependent on process formation.

Journal of Experimental Biology ◽

10.1242/jeb.174.1.215 ◽

1993 ◽

Vol 174 (1) ◽

pp. 215-233 ◽

Cited By ~ 3

Author(s):

D A Fadool ◽

W C Michel ◽

B W Ache

Keyword(s):

Voltage Clamp ◽

Olfactory Receptor ◽

Cell Voltage ◽

Response Spectra ◽

Olfactory Receptor Neurons ◽

Process Formation ◽

Receptor Neurons ◽

Dual Polarity ◽

Odor Sensitivity

Cultured lobster olfactory receptor neurons (ORNs) were surveyed for their odor sensitivity with whole-cell, voltage-clamp recording. The nature of the adequate stimuli, the degree of tuning (response spectra) of the cells, the threshold of sensitivity and the dual polarity of the odor-evoked currents are consistent with chemosensitivity in the cultured ORNs being olfactory. The ability of odors to evoke currents in cultured ORNs that lack processes suggests that lobster ORNs can be induced in vitro to insert all the elements of the transduction cascade in the soma, including those that might normally be confined to processes. This should greatly facilitate analysis of olfactory transduction in these cells.

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Characterization of macroscopic outward currents of canine colonic myocytes

AJP Cell Physiology ◽

10.1152/ajpcell.1989.257.3.c461 ◽

1989 ◽

Vol 257 (3) ◽

pp. C461-C469 ◽

Cited By ~ 25

Author(s):

W. C. Cole ◽

K. M. Sanders

Keyword(s):

Outward Current ◽

Cell Voltage ◽

Muscle Cells ◽

Time Dependent ◽

Delayed Rectifier ◽

Delayed Rectifier Current ◽

Outward Currents ◽

Voltage Dependent ◽

K Current ◽

Time Courses

Outward currents of colonic smooth muscle cells were characterized by the whole cell voltage-clamp method. Four components of outward current were identified: a time-independent and three time-dependent components. The time-dependent current showed strong outward rectification positive to -25 mV and was blocked by tetraethylammonium. The time-dependent components were separated on the basis of their time courses, voltage dependence, and pharmacological sensitivities. They are as follows. 1) A Ca2+-activated K current sensitive to external Ca2+ and Ca2+ influx was blocked by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (0.1 X 10(-3) M) and nifedipine (1 X 10(-6) and was increased by elevated Ca2+ (8 X 10(-6) M) and BAY K 8644 (1 X 10(-6) M). 2) A "delayed rectifier" current was observed that decayed slowly with time and showed no voltage-dependent inactivation. 3) Spontaneous transient outward currents that were blocked by ryanodine (2 X 10(-6) M) were also recorded. The possible contributions of these currents to the electrical activity of colonic muscle cells in situ are discussed. Ca2+-activated K current may contribute a significant conductance to the repolarizing phase of electrical slow waves.

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Functional properties of vertebrate olfactory receptor neurons

Physiological Reviews ◽

10.1152/physrev.1986.66.3.772 ◽

1986 ◽

Vol 66 (3) ◽

pp. 772-818 ◽

Cited By ~ 144

Author(s):

T. V. Getchell

Keyword(s):

Olfactory Receptor ◽

Olfactory Receptor Neuron ◽

Olfactory Nerve ◽

Sensory Transduction ◽

Olfactory Receptor Neurons ◽

Receptor Neuron ◽

Olfactory Pathway ◽

Receptor Neurons ◽

Molecular Biological Techniques

The interaction of an odorant with the chemosensitive membrane of olfactory receptor neurons initiates a sequence of molecular and membrane events leading to sensory transduction, impulse initiation, and the transmission of sensory information to the brain. The main steps in this sequence are summarized in Figure 6. Several lines of evidence support the hypothesis that the initial molecular events and subsequent stages of transduction are mediated by odorant receptor sites and associated ion channels located in the membrane of the cilia and apical dendritic knob of the olfactory receptor neuron. Similarly, the membrane events associated with impulse initiation and propagation are mediated by voltage-gated channels located in the initial axonal segment and the axolemma. The ionic and electrical events associated with the proposed sequence have been characterized in general using a variety of experimental techniques. The identification, localization, and sequence of membrane events are consistent with the neurophysiological properties observed in specific regions of the bipolar receptor neuron. The influence of other cells in the primary olfactory pathway such as the sustentacular cells in the olfactory epithelium, the Schwann cells in the olfactory nerve, and the astrocytes in the olfactory nerve layer in the olfactory bulb on the physiological activity of the olfactory receptor neuron is an emerging area of research interests. The general principles derived from the experimental results described in this review provide only a framework that is both incomplete and of necessity somewhat speculative. As noted in the Introduction, the multidisciplinary study of the primary olfactory pathway is undergoing a renaissance of research interest. The application of modern biophysical, cell, and molecular biological techniques to the basic issues of odorant recognition and membrane excitability will clarify the speculations and lead to the establishment of new hypotheses. Three broad areas of research will benefit from such studies. First, the application of biophysical techniques will lead to a detailed characterization of the membrane properties and associated ion conductance mechanisms. Second, the isolation and biochemical characterization of intrinsic membrane and cytosolic proteins associated with odorant recognition, sensory transduction, and the subsequent electrical events will result from the utilization of cell and molecular biological techniques.(ABSTRACT TRUNCATED AT 400 WORDS)

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Somatostatin increases voltage-dependent potassium currents in rat somatotrophs

AJP Cell Physiology ◽

10.1152/ajpcell.1990.259.6.c854 ◽

1990 ◽

Vol 259 (6) ◽

pp. C854-C861 ◽

Cited By ~ 40

Author(s):

C. Chen ◽

J. Zhang ◽

J. D. Vincent ◽

J. M. Israel

Keyword(s):

Growth Hormone ◽

Cell Voltage ◽

Inhibitory Effect ◽

Delayed Rectifier ◽

Hormone Release ◽

Growth Hormone Release ◽

Voltage Dependent ◽

Inward Currents ◽

K Current ◽

K Currents

To study the modulatory effects of somatostatin on membrane K+ currents, whole cell voltage-clamp recordings were performed on identified rat somatotrophs in primary culture. In the presence of Co2+ (2 mM) and tetrodotoxin (1 microM) in the bath solution to block Ca2+ and Na+ inward currents, two types of voltage-activated K+ currents were identified on the basis of their kinetics and pharmacology. First, a delayed rectifier K+ current (IK) had a threshold of -20 mV, did not decay during voltage steps lasting 300 ms, and was markedly attenuated by extracellular application of tetraethylammonium (TEA, 10 mM). Second, a transient outward K+ current (IA) was activated at -40 mV (from a holding potential of -80 mV) and persisted despite the presence of TEA. This IA was blocked by 4-aminopyridine (2 mM). Somatostatin (10 nM) increased IK by 75% and IA by 45% without obvious effects on steady-state voltage dependency of activation or inactivation, and these effects were reversible. This increase in K+ currents may contribute in part to the inhibitory effect of somatostatin on growth hormone release.

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