scholarly journals Mechanism of olfactory masking in the sensory cilia

2009 ◽  
Vol 133 (6) ◽  
pp. 583-601 ◽  
Author(s):  
Hiroko Takeuchi ◽  
Hirohiko Ishida ◽  
Satoshi Hikichi ◽  
Takashi Kurahashi
Keyword(s):  
Signal Transmission ◽  
Ca Channel ◽  
Ca Channels ◽  
Caged Compounds ◽  
Whole Cell Patch Clamp ◽  
Cng Channel ◽  
Sensory Cilia ◽  
Ultraviolet Photolysis ◽  
Masking Agents ◽  
Nonlinear Signal

Olfactory masking has been used to erase the unpleasant sensation in human cultures for a long period of history. Here, we show a positive correlation between the human masking and the odorant suppression of the transduction current through the cyclic nucleotide–gated (CNG) and Ca2+-activated Cl− (Cl(Ca)) channels. Channels in the olfactory cilia were activated with the cytoplasmic photolysis of caged compounds, and their sensitiveness to odorant suppression was measured with the whole cell patch clamp. When 16 different types of chemicals were applied to cells, cyclic AMP (cAMP)-induced responses (a mixture of CNG and Cl(Ca) currents) were suppressed widely with these substances, but with different sensitivities. Using the same chemicals, in parallel, we measured human olfactory masking with 6-rate scoring tests and saw a correlation coefficient of 0.81 with the channel block. Ringer's solution that was just preexposed to the odorant-containing air affected the cAMP-induced current of the single cell, suggesting that odorant suppression occurs after the evaporation and air/water partition of the odorant chemicals at the olfactory mucus. To investigate the contribution of Cl(Ca), the current was exclusively activated by using the ultraviolet photolysis of caged Ca, DM-nitrophen. With chemical stimuli, it was confirmed that Cl(Ca) channels were less sensitive to the odorant suppression. It is interpreted, however, that in the natural odorant response the Cl(Ca) is affected by the reduction of Ca2+ influx through the CNG channels as a secondary effect. Because the signal transmission between CNG and Cl(Ca) channels includes nonlinear signal-boosting process, CNG channel blockage leads to an amplified reduction in the net current. In addition, we mapped the distribution of the Cl(Ca) channel in living olfactory single cilium using a submicron local [Ca2+]i elevation with the laser photolysis. Cl(Ca) channels are expressed broadly along the cilia. We conclude that odorants regulate CNG level to express masking, and Cl(Ca) in the cilia carries out the signal amplification and reduction evenly spanning the entire cilia. The present findings may serve possible molecular architectures to design effective masking agents, targeting olfactory manipulation at the nano-scale ciliary membrane.

scholarly journals Internal and external effects of dihydropyridines in the calcium channel of skeletal muscle.

1990 ◽  
Vol 95 (1) ◽  
pp. 1-27 ◽  
Author(s):  
H H Valdivia ◽  
R Coronado
Keyword(s):  
Skeletal Muscle ◽  
Lipid Bilayers ◽  
Radioligand Binding ◽  
Quantitative Agreement ◽  
Bay K 8644 ◽  
Single Channels ◽  
Ca Channel ◽  
Ca Channels ◽  
Receptor Sites ◽  
Internal Side

The agonist effect of the dihydropyridine (DHP) (-)Bay K 8644 and the inhibitory effects of nine antagonist DHPs were studied at a constant membrane potential of 0 mV in Ca channels of skeletal muscle transverse tubules incorporated into planar lipid bilayers. Four phenylalkylamines (verapamil, D600, D575, and D890) and d-cis-diltiazem were also tested. In Ca channels activated by 1 microM Bay K 8644, the antagonists nifedipine, nitrendipine, PN200-110, nimodipine, and pure enantiomer antagonists (+)nimodipine, (-)nimodipine, (+)Bay K 8644, inhibited activity in the concentration range of 10 nM to 10 microM. Effective doses (ED50) were 2 to 10 times higher when HDPs were added to the internal side than when added to the external side. This sidedness arises from different structure-activity relationships for DHPs on both sides of the Ca channel since the ranking potency of DHPs is PN200-110 greater than (-)nimodipine greater than nifedipine approximately S207-180 on the external side while PN200-110 greater than S207-180 greater than nifedipine approximately (-)nimodipine on the internal side. A comparison of ED50's for inhibition of single channels by DHPs added to the external side and ED50's for displacement of [3H]PN200-110 bound to the DHP receptor, revealed a good quantitative agreement. However, internal ED50's of channels were consistently higher than radioligand binding affinities by up to two orders of magnitude. Evidently, Ca channels of skeletal muscle are functionally coupled to two DHP receptor sites on opposite sides of the membrane.

Voltage Sensitive Ca-Channels and the Transient Inward Current in Paramecium Tetraurelia

1979 ◽  
Vol 78 (1) ◽  
pp. 149-161 ◽  
Author(s):  
YOUKO SATOW ◽  
CHING KUNG
Keyword(s):  
Voltage Clamp ◽  
Resting Potential ◽  
Ca Channel ◽  
Paramecium Tetraurelia ◽  
Ca Channels ◽  
Action Current ◽  
Inward Current ◽  
Transient Inward Current ◽  
Inorganic Cation ◽  
Inward Currents

Transient inward currents across the membrane of P. tetraurelia are recorded upon step depolarizations with a voltage clamp in solutions where Ca2+ is the only added inorganic cation. It is shown that the current is normally carried by Ca2+ through the Ca-channels which activate and inactivate in time. The transient inward current is dependent on both the size of the depolarizing step and the holding level before the step. Maximum inward current (Imax) occurs when the membrane is first held at the resting level (- 30 mV), then stepped to 0 mV in a solution containing 0.91 mM-Ca2+. The Imax is smaller when the membrane is first held at depolarized level. This is due to the depolarization-sensitive inactivation of the Ca-channels. The Imax is also smaller when the membrane is first held at a hyperpolarized level. This may be explained by the activation of hyperpolarization-sensitive K-channels known to exist in the Paramecium membrane. I max increases with concentration of Ca2+ up to 0.9 mM. Further increase in the Ca2+ concentration does not affect Imax. This apparent saturation at 0.9 mM-Ca2+ may reflect a rate-limiting step of Ca2+ permeation. The increase in Ca2+ concentration shifts the V-Ipeak curve in the direction of less sensitivity. This result is best explained as the effect of bound Ca2+ on the surface potential of the Paramecium membrane. These results provide the first detailed description of the properties of the action current through the Ca-channel in Paramecium. They also define the conditions under which future voltage-clamp studies of wild-type and mutant membranes of P. tetraurelia should be performed, i.e. to maximize the resolution of the Ca-channel activity, the membrane should be held at or near the resting potential and there should be over 0.9 mM-Ca2+ in the test solutions. The behaviour of the Paramecium Ca-channel and small Imax in the presence of K+ are discussed.

Enhanced single-channel K+ current in arterial membranes from genetically hypertensive rats

1993 ◽  
Vol 264 (5) ◽  
pp. H1337-H1345 ◽  
Author(s):  
S. K. England ◽  
T. A. Wooldridge ◽  
W. J. Stekiel ◽  
N. J. Rusch
Keyword(s):  
Single Channel ◽  
Muscle Cells ◽  
Ca Channel ◽  
Ca Channels ◽  
Hypertensive Rats ◽  
Genetically Hypertensive Rats ◽  
K Current ◽  
Inside Out ◽  
Genetically Hypertensive ◽  
Arterial Muscle

Arterial smooth muscle from hypertensive rats shows an increased membrane permeability to K+ that depends on Ca2+ influx. To define the mechanism of this membrane alteration, we tested the hypothesis that Ca(2+)-dependent K+ current (IK(Ca)) is increased in arterial muscle membranes from genetically hypertensive rats. Single-channel K+ currents measured in cell-attached and inside-out aortic membrane patches from spontaneously hypertensive rats (SHR) were compared with those from normotensive Wistar-Kyoto rats (WKY). Inside-out patches from both rat strains showed a predominant 225 pS, Ca(2+)- and voltage-dependent K+ channel in symmetrical 145 mM KCl solutions, which was blocked by tetraethylammonium [concentration for half-maximal block (IC50) < or = 0.3 mM]. In cell-attached patches of aortic muscle cells bathed in physiological salt solution, this channel [IK(Ca) channel] showed a fivefold higher open-state probability (NPo) in SHR as compared with WKY. This increased NPo of SHR IK(Ca) channels in membranes of intact aortic muscle cells was not correlated with an altered membrane potential in current-clamped SHR myocytes or with changes in cytosolic free Ca2+ concentration in fura-2-loaded aortic muscle cells. However, inside-out aortic membrane patches from SHR showed more detected IK(Ca) channels per patch, a higher IK(Ca) channel NPo, and a greater total patch current than their WKY counterparts. Further analysis revealed a greater Ca2+ sensitivity of SHR than WKY IK(Ca) channels. These results suggest that IK(Ca) channel function is altered in isolated membrane patches of arterial muscle from genetically hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular Insights into Regulation of L-Type Ca Channel Function

Physiology ◽  
1991 ◽  
Vol 6 (6) ◽  
pp. 277-281 ◽  
Author(s):  
P Lory ◽  
G Varadi ◽  
A Schwartz
Keyword(s):  
Structure Function ◽  
Splice Variants ◽  
Ca Channel ◽  
Gene Products ◽  
Ca Channels ◽  
Channel Activity ◽  
Excitable Cells ◽  
Multiple Gene ◽  
Channel Function ◽  
Voltage Dependent

The diversity of voltage-dependent Ca channels is well documented. How excitable cells produce their specific Ca channel activity is being approached by structure-function studies. The implications of multiple gene products, splice variants, and subunit assembly in Ca channel function are updated in this review.

Spike-Mediated and Graded Inhibitory Synaptic Transmission Between Leech Interneurons: Evidence for Shared Release Sites

2006 ◽  
Vol 96 (1) ◽  
pp. 235-251 ◽  
Author(s):  
Andrei I. Ivanov ◽  
Ronald L. Calabrese
Keyword(s):  
Synaptic Transmission ◽  
Synaptic Vesicles ◽  
Low Voltage ◽  
Release Site ◽  
High Threshold ◽  
Channel Blockers ◽  
Ca Channel ◽  
Ca Channels ◽  
Inhibitory Synaptic Transmission ◽  
Graded Release

Inhibitory synaptic transmission between leech heart interneurons consist of two components: graded, gated by Ca2+ entering by low-threshold [low-voltage–activated (LVA)] Ca channels and spike-mediated, gated by Ca2+ entering by high-threshold [high-voltage–activated (HVA)] Ca channels. Changes in presynaptic background Ca2+ produced by Ca2+ influx through LVA channels modulate spike-mediated transmission, suggesting LVA channels have access to release sites controlled by HVA channels. Here we explore whether spike-mediated and graded transmission can use the same release sites and thus how Ca2+ influx by HVA and LVA Ca channels might interact to evoke neurotransmitter release. We recorded pre- and postsynaptic currents from voltage-clamped heart interneurons bathed in 0 mM Na+/5 mM Ca2+ saline. Using different stimulating paradigms and inorganic Ca channel blockers, we show that strong graded synaptic transmission can occlude high-threshold/spike-mediated synaptic transmission when evoked simultaneously. Suppression of LVA Ca currents diminishes graded release and concomitantly increases the ability of Ca2+ entering by HVA channels to release transmitter. Uncaging of Ca chelator corroborates that graded release occludes spike-mediated transmission. Our results indicate that both graded and spike-mediated synaptic transmission depend on the same readily releasable pool of synaptic vesicles. Thus Ca2+, entering cells through different Ca channels (LVA and HVA), acts to gate release of the same synaptic vesicles. The data argue for a closer location of HVA Ca channels to release sites than LVA Ca channels. The results are summarized in a conceptual model of a heart interneuron release site.

Differential responses of Ca-activated K channels to bradykinin in sensory neurons and F-11 cells

1992 ◽  
Vol 262 (2) ◽  
pp. C453-C460 ◽  
Author(s):  
K. Naruse ◽  
D. S. McGehee ◽  
G. S. Oxford
Keyword(s):  
Intracellular Signaling ◽  
Single Channel ◽  
Outward Current ◽  
Transient Outward Current ◽  
Ca Channel ◽  
Ca Channels ◽  
Drg Neurons ◽  
Open Probability ◽  
K Channels ◽  
Drg Neuron

The nonapeptide bradykinin (BK) excites a subset of dorsal root ganglion (DRG) neurons with putative nociceptive functions by stimulating an inward cation current. In addition, BK stimulates various intracellular signaling pathways including an elevation of intracellular Ca2+. In a DRG neuron x neuroblastoma hybrid cell (F-11), BK stimulates similar increases in intracellular [Ca2+] and inward current but also elicits a large transient outward current through Ca(2+)-activated K channels. We have investigated the mechanisms underlying differential expression of outward current responses in the two cell types at the single channel level. Although K(Ca) channel activity appears in inside-out patches from both cells exposed to Ca2+, BK applied to the extrapatch membrane of cell-attached patches activates K(Ca) channels in F-11 but not DRG neurons. Whereas single K(Ca) channels are quantitatively similar in terms of conductance, voltage-dependence, and sensitivity to tetraethylammonium, they differ in sensitivity to intracellular Ca2+. Channel activation in both cells requires at least four Ca2+ ions, but half-maximal activation occurs at slightly higher [Ca2+] for DRG neurons. The shift in the Ca2+ dose-response curve combined with the steep [Ca2+] dependence of channel open probability makes it less likely that a BK-induced rise in internal [Ca2+] induced will trigger a transient outward current and resultant hyperpolarization in a DRG neuron.

Effects of estrogens on Ca channels in myometrial cells isolated from pregnant rats

1995 ◽  
Vol 268 (1) ◽  
pp. C64-C69 ◽  
Author(s):  
T. Yamamoto
Keyword(s):  
Steady State ◽  
Ca Channel ◽  
Ca Channels ◽  
Inhibitory Effects ◽  
Inactivation Curve ◽  
Pregnant Rat ◽  
Negative Direction ◽  
Myometrial Cells ◽  
Steady State Inactivation ◽  
Channel Currents

Whole cell patch-clamp techniques were applied to cultured smooth muscle cells isolated from the longitudinal layer of the late pregnant rat myometrium. Effects of estrogens on Ca channels were examined. Inhibitory effects of beta-estradiol (1 microM) on Ca channel currents were recognized. The inhibitory effects of beta-estradiol depended on holding potentials. beta-Estradiol shifted the steady-state inactivation curve in the negative direction by 7 mV at mid potential (n = 9). Diethylstilbestrol, a synthetic estrogen, gave similar effects on Ca channel currents at lower concentration (2 microM) to those of beta-estradiol. Strong inhibitory effects on Ca channel currents were obtained by higher concentration (20 microM). Diethylstilbestrol shifted the steady-state inactivation curve in the negative direction by 7 mV at mid potential (n = 5). The results indicate that estrogens influence the voltage dependency and the whole cell conductance of Ca channels of pregnant rat myometrial cells. The acute effect of estrogens may cause both electrical and mechanical depression of myometrium.

scholarly journals Cardiac calcium channels in planar lipid bilayers. L-type channels and calcium-permeable channels open at negative membrane potentials.

1988 ◽  
Vol 92 (1) ◽  
pp. 27-54 ◽  
Author(s):  
R L Rosenberg ◽  
P Hess ◽  
R W Tsien
Keyword(s):  
Lipid Bilayers ◽  
Single Channel ◽  
Detailed Comparison ◽  
Membrane Potentials ◽  
Bay K 8644 ◽  
Ca Channel ◽  
Ca Channels ◽  
Channel Activity ◽  
Intact Cells ◽  
Free System

Planar lipid bilayer recordings were used to study Ca channels from bovine cardiac sarcolemmal membranes. Ca channel activity was recorded in the absence of nucleotides or soluble enzymes, over a range of membrane potentials and ionic conditions that cannot be achieved in intact cells. The dihydropyridine-sensitive L-type Ca channel, studied in the presence of Bay K 8644, was identified by a detailed comparison of its properties in artificial membranes and in intact cells. L-type Ca channels in bilayers showed voltage dependence of channel activation and inactivation, open and closed times, and single-channel conductances in Ba2+ and Ca2+ very similar to those found in cell-attached patch recordings. Open channels were blocked by micromolar concentrations of external Cd2+. In this cell-free system, channel activity tended to decrease during the course of an experiment, reminiscent of Ca2+ channel "rundown" in whole-cell and excised-patch recordings. A purely voltage-dependent component of inactivation was observed in the absence of Ca2+ stores or changes in intracellular Ca2+. Millimolar internal Ca2+ reduced unitary Ba2+ influx but did not greatly increase the rate or extent of inactivation or the rate of channel rundown. In symmetrical Ba2+ solutions, unitary conductance saturated as the Ba2+ concentration was increased up to 500 mM. The bilayer recordings also revealed activity of a novel Ca2+-permeable channel, termed "B-type" because it may contribute a steady background current at negative membrane potentials, which is distinct from L-type or T-type Ca channels previously reported. Unlike L-type channels, B-type channels have a small unitary Ba2+ conductance (7 pS), but do not discriminate between Ba2+ and Ca2+, show no obvious sensitivity to Bay K 8644, and do not run down. Unlike either L- or T-type channels, B-type channels did not require a depolarization for activation and displayed mean open times of greater than 100 ms.

scholarly journals Regulators of G Protein Signaling Attenuate the G Protein–mediated Inhibition of N-Type Ca Channels

1999 ◽  
Vol 113 (1) ◽  
pp. 97-110 ◽  
Author(s):  
Karim Melliti ◽  
Ulises Meza ◽  
Rory Fisher ◽  
Brett Adams
Keyword(s):  
G Protein ◽  
G Proteins ◽  
G Protein Signaling ◽  
Rgs Proteins ◽  
Ca Channel ◽  
Protein Signaling ◽  
Ca Channels ◽  
Channel Inhibition ◽  
Kinetics Of ◽  
In Cells

Regulators of G protein signaling (RGS) proteins bind to the α subunits of certain heterotrimeric G proteins and greatly enhance their rate of GTP hydrolysis, thereby determining the time course of interactions among Gα, Gβγ, and their effectors. Voltage-gated N-type Ca channels mediate neurosecretion, and these Ca channels are powerfully inhibited by G proteins. To determine whether RGS proteins could influence Ca channel function, we recorded the activity of N-type Ca channels coexpressed in human embryonic kidney (HEK293) cells with G protein–coupled muscarinic (m2) receptors and various RGS proteins. Coexpression of full-length RGS3T, RGS3, or RGS8 significantly attenuated the magnitude of receptor-mediated Ca channel inhibition. In control cells expressing α1B, α2, and β3 Ca channel subunits and m2 receptors, carbachol (1 μM) inhibited whole-cell currents by ∼80% compared with only ∼55% inhibition in cells also expressing exogenous RGS protein. A similar effect was produced by expression of the conserved core domain of RGS8. The attenuation of Ca current inhibition resulted primarily from a shift in the steady state dose–response relationship to higher agonist concentrations, with the EC50 for carbachol inhibition being ∼18 nM in control cells vs. ∼150 nM in RGS-expressing cells. The kinetics of Ca channel inhibition were also modified by RGS. Thus, in cells expressing RGS3T, the decay of prepulse facilitation was slower, and recovery of Ca channels from inhibition after agonist removal was faster than in control cells. The effects of RGS proteins on Ca channel modulation can be explained by their ability to act as GTPase-accelerating proteins for some Gα subunits. These results suggest that RGS proteins may play important roles in shaping the magnitude and kinetics of physiological events, such as neurosecretion, that involve G protein–modulated Ca channels.

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