scholarly journals Cyclic nucleotide-gated channels of rat olfactory receptor cells: divalent cations control the sensitivity to cAMP.

1994 ◽  
Vol 103 (1) ◽  
pp. 87-106 ◽  
Author(s):  
J W Lynch ◽  
B Lindemann
Keyword(s):  
Cyclic Nucleotide ◽  
Olfactory Receptor ◽  
Divalent Cations ◽  
Membrane Surface ◽  
Regulatory Protein ◽  
Induced Response ◽  
Intact Cells ◽  
Cyclic Nucleotide Gated Channels ◽  
Olfactory Receptor Cells ◽  
Receptor Cells

cAMP-gated channels were studied in inside-out membrane patches excised from the apical cellular pole of isolated olfactory receptor cells of the rat. In the absence of divalent cations the dose-response curve of activation of patch current by cAMP had a KM of 4.0 microM at -50 mV and of 2.5 microM at +50 mV. However, addition of 0.2 or 0.5 mM Ca2+ shifted the KM of cAMP reversibly to the higher cAMP concentrations of 33 or 90 microM, respectively, at -50 mV. Among divalent cations, the relative potency for inducing cAMP affinity shifts was: Ca2+ > Sr2+ > Mn2+ > Ba2+ > Mg2+, of which Mg2+ (up to 3 mM) did not shift the KM at all. This potency sequence corresponds closely to that required for the activation of calmodulin. However, the Ca(2+)-sensitivity is lower than expected for a calmodulin-mediated action. Brief (60 s) transient exposure to 3 mM Mg2+, in the absence of other divalent cations, had a protective effect in that following washout of Mg2+, subsequent exposure to 0.2 mM Ca2+ no longer caused affinity shifts. This protection effect did not occur in intact cells and was probably a consequence of patch excision, possibly representing ablation of a regulatory protein from the channel cyclic nucleotide binding site. Thus, the binding of divalent cations, probably via a regulatory protein, controls the sensitivity of the cAMP-gated channels to cAMP. The influx of Ca2+ through these channels during the odorant response may rise to a sufficiently high concentration at the intracellular membrane surface to contribute to the desensitization of the odorant-induced response. The results also indicate that divalent cation effects on cyclic nucleotide-gated channels may depend on the sequence of pre-exposure to other divalent cations.

scholarly journals Properties of cyclic nucleotide-gated channels mediating olfactory transduction. Activation, selectivity, and blockage.

1992 ◽  
Vol 100 (1) ◽  
pp. 45-67 ◽  
Author(s):  
S Frings ◽  
J W Lynch ◽  
B Lindemann
Keyword(s):  
Cyclic Nucleotide ◽  
Olfactory Receptor ◽  
Cation Binding ◽  
Ph Effects ◽  
Induced Current ◽  
Cyclic Nucleotide Gated Channels ◽  
Olfactory Receptor Cells ◽  
Receptor Cells ◽  
Cation Binding Site ◽  
Voltage Dependent

Cyclic nucleotide-gated channels (cng channels) in the sensory membrane of olfactory receptor cells, activated after the odorant-induced increase of cytosolic cAMP concentration, conduct the receptor current that elicits electrical excitation of the receptor neurons. We investigated properties of cng channels from frog and rat using inside-out and outside-out membrane patches excised from isolated olfactory receptor cells. Channels were activated by cAMP and cGMP with activation constants of 2.5-4.0 microM for cAMP and 1.0-1.8 for cGMP. Hill coefficients of dose-response curves were 1.4-1.8, indicating cooperativity of ligand binding. Selectivity for monovalent alkali cations and the Na/Li mole-fraction behavior identified the channel as a nonselective cation channel, having a cation-binding site of high field strength in the pore. Cytosolic pH effects suggest the presence of an additional titratable group which, when protonated, inhibits the cAMP-induced current with an apparent pK of 5.0-5.2. The pH effects were not voltage dependent. Several blockers of Ca2+ channels also blocked olfactory cng channels. Amiloride, D 600, and diltiazem inhibited the cAMP-induced current from the cytosolic side. Inhibition constants were voltage dependent with values of, respectively, 0.1, 0.3, and 1 mM at -60 mV, and 0.03, 0.02, and 0.2 mM at +60 mV. Our results suggest functional similarity between frog and rat cng channels, as well as marked differences to cng channels from photoreceptors and other tissues.

Genesis of cilia and microvilli of rat nasal epithelia during pre-natal development. II. Olfactory epithelium, a morphometric analysis

1985 ◽  
Vol 78 (1) ◽  
pp. 311-336
Author(s):  
B.P. Menco ◽  
A.I. Farbman
Keyword(s):  
Olfactory Receptor ◽  
Primary Cilia ◽  
Average Rate ◽  
Membrane Surface ◽  
Supporting Cells ◽  
Epithelial Surface ◽  
Olfactory Cilia ◽  
Olfactory Receptor Cells ◽  
Receptor Cells ◽  
Multiciliated Cells

Rat foetuses from intra-uterine days E14 through E22 (day before parturition) and adults were used for a quantitative scanning electron-microscopic examination of ciliogenesis in olfactory receptor cells and microvillogenesis in olfactory supporting cells. Four developmental stages in olfactory ciliogenesis can be discerned. Two of these are characterized by the presence of primary cilia only, the other two concern outgrowth in number and length of secondary cilia. (1) Primary cilia on undifferentiated cells; this stage occurs up to E14. (2) Primary cilia on differentiating olfactory receptor and also olfactory supporting cells. This stage begins at E14 and lasts, for the olfactory receptor cells, at least up to E22. On the supporting cells primary cilia are rarely observed after E18. Virtually all primary cilia are about 1 micron long. Up to E21 dendritic endings with primary cilia occur more frequently than those with any other number of cilia; all endings have a transitional stage in which they bear primary cilia only. (3) Secondary olfactory cilia increase in number. From E16 onwards the cells become multiciliated. Beginning at this stage and continuing up to E22 an average of one cilium per day is added to the endings. At E22 the average number of cilia observed per ending is about 70% of that in adults; more than 90% of the endings are multiciliated. From E15 to E22 the exchange rate between receptor cells with only primary cilia and multiciliated cells is about 0.5 X 10(6) cells/cm2 per day. When considered in the light of electrophysiological data on developing rats, our data suggest that when the cells have just primary cilia, they may respond indiscriminately to all odorants, whereas multiciliated cells display odorant specificity. (4) Secondary olfactory cilia increase in length. From E14 to E19 and over the whole population of receptor cells the cilia grow at an average rate of about 0.5 micron/day. Proximal parts of olfactory cilia are longer than primary cilia; olfactory cilia begin to taper in increasing numbers around E18. At E19 the receptive membrane surface, i.e. regions of the cells facing the nasal lumen, of individual cells is about 8%, and the increase in epithelial surface due to sprouting of cilia is 5% of such values in adult animals. Concomitant with the onset of tapering of olfactory cilia, i.e. around E18, microvilli of supporting cells show a spurt in growth from about 0.4 micron to about 1.3 micron. Unlike olfactory cilia they show no growth, on average, after E19.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Na+-dependent Ca2+ Extrusion Governs Response Recovery in Frog Olfactory Receptor Cells

1998 ◽  
Vol 112 (5) ◽  
pp. 529-535 ◽  
Author(s):  
Johannes Reisert ◽  
H.R. Matthews
Keyword(s):  
Cyclic Nucleotide ◽  
Olfactory Receptor ◽  
Ionic Composition ◽  
External Solution ◽  
Free Solution ◽  
Olfactory Cilia ◽  
Olfactory Receptor Cells ◽  
Receptor Cells ◽  
Response Recovery ◽  
Extrusion Mechanism

To study the mechanism by which Ca2+, which enters during the odor response, is extruded during response recovery, recordings were made from isolated frog olfactory receptor cells using the suction pipette technique, while superfusing the olfactory cilia with solutions of modified ionic composition. When external Na+ was substituted with another cation, the response to odor was greatly prolonged. This prolongation of the response was similar irrespective of whether Na+ was replaced with Li+, which permeates the cyclic nucleotide-gated conductance, or choline, which does not. The prolonged current was greatly reduced by exposure to 300 μM niflumic acid, a blocker of the calcium-activated chloride channel, indicating that it is carried by this conductance, and abolished if Ca2+ was omitted from the external solution, demonstrating that Ca2+ influx is required for its generation. When the cilia were exposed to Na+-free solution after odor stimulation, the recovery of the response to a second stimulus from the adaptation induced by the first was greatly reduced. We conclude that a Na+-dependent Ca2+ extrusion mechanism is present in frog olfactory cilia and that it serves as the main mechanism that returns cytoplasmic Ca2+ concentration to basal levels after stimulation and mediates the normally rapid recovery of the odor response and the restoration of sensitivity after adaptation.

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