Biochemical properties of the sensitivity to GABAAergic ligands, Cl-/HCO3--ATPase isolated from fish (Cyprinus carpio) olfactory mucosa and brain.

This paper presents a comparative study of the roles of Cl- and HCO3- in the functioning of the GABAAR-associated Cl-/HCO3--ATPase of the plasma membranes of the olfactory sensory neurons (OSNs) and mature brain neurons (MBNs) of fish. The ATPase activity of OSNs and its dephosphorylation were increased twofold by Cl-(15-30 mmol l-1), whereas the enzyme from MBNs was not significantly affected by Cl-. By contrast, HCO3-(15-30 mmol l-1) significantly activated the MBN enzyme and its dephosphorylation, but had no effect on the OSN ATPase. The maximum ATPase activity and protein dephosphorylation was observed in the presence of both Cl-(15 mmol l-1)/HCO3-(27 mmol l-1) and these activities were inhibited in the presence of picrotoxin (100 µmol l-1), bumetanide (150 µmol l-1), and DIDS (1000 µmol l-1). SDS-PAGE revealed that ATPases purified from the neuronal membrane have a subunit with molecular mass of ~ 56 kDa that binds [3H]muscimol and [3H]flunitrazepam. Direct phosphorylation of the enzymes in the presence of ATP-γ-32P and Mg2+, as well as Cl-/HCO3- sensitive dephosphorylation, is also associated with this 56 kDa peptide. Both preparations also showed one subunit with molecular mass 56 kDa that was immunoreactive with GABAAR ß3 subunit. The use of a fluorescent dye for Cl- demonstrated that HCO3-(27 mmol l-1) causes a twofold increase in Cl- influx into proteoliposomes containing reconstituted ATPases from MBNs, but HCO3- had no effect on the reconstituted enzyme from OSNs. These data are the first to demonstrate a differential effect of Cl- and HCO3- in the regulation of the Cl-/HCO3--ATPases functioning in neurons with different specializations.

Odorant Metabolism Analysis by an Automated Ex Vivo Headspace Gas-Chromatography Method.

In the olfactory epithelium (OE), odorant metabolizing enzymes have the dual function of volatile component detoxification and active clearance of odorants from the perireceptor environment to respectively maintain the integrity of the tissues and the sensitivity of the detection. Although emphasized by recent studies, this enzymatic mechanism is poorly documented in mammals. Thus, olfactory metabolism has been characterized mainly in vitro and for a limited number of odorants. The automated ex vivo headspace gas-chromatography method that was developed here was validated to account for odorant olfactory metabolism. This method easily permits the measurement of the fate of an odorant in the OE environment, taking into account the odorant gaseous state and the cellular structure of the tissue, under experimental conditions close to physiological conditions and with a high reproducibility. We confirmed here our previous results showing that a high olfactory metabolizing activity of the mammary pheromone may be necessary to maintain a high level of sensitivity toward this molecule, which is critical for newborn rabbit survival. More generally, the method that is presented here may permit the screening of odorants metabolism alone or in mixture or studying the impact of aging, pathology, polymorphism or inhibitors on odorant metabolism.

Essential role of the cytochrome P450 enzyme CYP2A5 in olfactory mucosal toxicity of naphthalene.

Naphthalene (NA), a ubiquitous environmental pollutant that can cause pulmonary and nasal toxicity in laboratory animals, requires cytochrome P450 (P450)-mediated metabolic activation to cause toxicity. Our recent study using a Cyp2f2-null mouse showed that CYP2F2 plays an essential role in NA-induced lung toxicity, but not in NA-induced nasal toxicity. The aim of this study was to determine whether mouse CYP2A5, abundantly expressed in nasal olfactory mucosa (OM) and the liver, but less in the lung, plays a major role in the bioactivation and toxicity of NA in the OM. We found, by comparing Cyp2a5-null and wild-type (WT) mice, that the loss of CYP2A5 expression led to substantial decreases in rates of NA metabolic activation by OM microsomes. The loss of CYP2A5 did not cause changes in systemic clearance of NA (at 200 mg/kg, i.p.). However, the Cyp2a5-null mice were much more resistant than were WT mice to NA-induced nasal toxicity (although not lung toxicity), when examined at 24 hours after NA dosing (at 200 mg/kg, i.p.), or to NA-induced depletion of total nonprotein sulfhydryl in the OM (although not in the lung), examined at 2 hours after dosing. Thus, mouse CYP2A5 plays an essential role in the bioactivation and toxicity of NA in the OM, but not in the lung. Our findings further illustrate the tissue-specific nature of the role of individual P450 enzymes in xenobiotic toxicity, and provide the basis for a more reliable assessment of the potential risks of NA nasal toxicity in humans.

Inhibition of glycogen synthase kinase-3 enhances the differentiation and reduces the proliferation of adult human olfactory epithelium neural precursors.

The olfactory epithelium (OE) contains neural precursor cells which can be easily harvested from a minimally invasive nasal biopsy, making them a valuable cell source to study human neural cell lineages in health and disease. Glycogen synthase kinase-3 (GSK-3) has been implicated in the etiology and treatment of neuropsychiatric disorders and also in the regulation of murine neural precursor cell fate in vitro and in vivo. In this study, we examined the impact of decreased GSK-3 activity on the fate of adult human OE neural precursors in vitro. GSK-3 inhibition was achieved using ATP-competitive (6-bromoindirubin-3'-oxime and CHIR99021) or substrate-competitive (TAT-eIF2B) inhibitors to eliminate potential confounding effects on cell fate due to off-target kinase inhibition. GSK-3 inhibitors decreased the number of neural precursor cells in OE cell cultures through a reduction in proliferation. Decreased proliferation was not associated with a reduction in cell survival but was accompanied by a reduction in nestin expression and a substantial increase in the expression of the neuronal differentiation markers MAP1B and neurofilament (NF-M) after 10 days in culture. Taken together, these results suggest that GSK-3 inhibition promotes the early stages of neuronal differentiation in cultures of adult human neural precursors and provide insights into the mechanisms by which alterations in GSK-3 signaling affect adult human neurogenesis, a cellular process strongly suspected to play a role in the etiology of neuropsychiatric disorders.

The tissue-specific toxicity of methimazole in the mouse olfactory mucosa is partly mediated through target-tissue metabolic activation by CYP2A5.

The antithyroid drug methimazole (MMZ) can cause severe, tissue-specific toxicity in mouse olfactory mucosa (OM), presumably through a sequential metabolic activation of MMZ by cytochrome P450 (P450) and flavin monooxygenases (FMO). The aims of this study were to determine whether CYP2A5, one of the most abundant P450 enzymes in the mouse OM, is involved in MMZ metabolic activation, by comparing Cyp2a5-null with wild-type (WT) mice, and whether hepatic microsomal P450 enzymes, including CYP2A5, are essential for MMZ-induced OM toxicity, by comparing liver-Cpr-null (LCN) mice, which have little P450 activity in hepatocytes, with WT mice. We showed that the loss of CYP2A5 expression did not alter systemic clearance of MMZ (at 50 mg/kg, i.p.); but it did significantly decrease the rates of MMZ metabolism in the OM, whereas FMO expression in the OM was not reduced. MMZ induced depletion of nonprotein thiols, as well as pathological changes, in the OM of WT mice; the extent of these changes was much reduced in the Cyp2a5-null mice. Thus, CYP2A5 plays an important role in mediating MMZ toxicity in the OM. In contrast, the rate of systemic clearance of MMZ was significantly reduced in the LCN mice, compared to WT mice, whereas the MMZ-induced OM toxicity was not prevented. Therefore, hepatic P450 enzymes are essential for systemic MMZ clearance, but they are not required for MMZ-induced OM toxicity. We conclude that the tissue-specific toxicity of MMZ is mediated by target tissue metabolic activation, and the reaction is partly catalyzed by CYP2A5 in the OM.

Localization of eNOS in the olfactory epithelium of the rat.

Nitric oxide (NO) is a free radical and produced from L-arginine by nitric oxide synthase (NOS). Since NO is recently suggested to be involved in olfactory perception, the expression of eNOS, an isoform of NOS, was examined in the rat olfactory epithelium. The activity of NADPH-diaphorase was also examined as a marker of NOS. In the dorsomedial region of the nasal cavity, intensely positive reactions for NADPH-diaphorase were observed in the entire cytoplasm of sensory cells (olfactory cells). By immunohistochemistry, intensely positive reactions for eNOS were also found in the dorsomedial region of the nasal cavity. These reactions were observed on the free border of the olfactory epithelium. By immunoelectron microscopy, positive reactions for eNOS were found in the cilia of olfactory cells. In addition, in situ hybridization analysis of the olfactory epithelium revealed the expression of eNOS mRNA in the olfactory cells. These results indicate the presence of eNOS in the olfactory cells of the rat, and differential expression of eNOS in the olfactory epithelium depending on the regions of the nasal cavity. In addition, NO produced by eNOS may be involved in olfactory perception in the cilia of olfactory cells.

Effects of typical inducers on olfactory xenobiotic-metabolizing enzyme, transporter, and transcription factor expression in rats.

Several xenobiotic-metabolizing enzymes (XMEs) have been identified in the olfactory mucosa (OM) of mammals. However, the molecular mechanisms underlying the regulation of these enzymes have been little explored. In particular, information on the expression of the transcriptional factors in this tissue is quite limited. The aim of the present study was to examine the impact of five typical inducers, Aroclor 1254, 3-methylcholanthrene, dexamethasone, phenobarbital, and ethoxyquin, on the activities and mRNA expression of several XMEs in the OM and in the liver of rats. We also evaluated the effects of these treatments on the mRNA expression of transcription factors and transporters. On the whole, the intensities of the effects were lower in the OM than in the liver. Dexamethasone was found to be the most efficient treatment in the OM. Dexamethasone induced the transcription of several olfactory phase I, II, and III genes [such as cytochromes P450 2A3 and 3A9, UDP-glucuronosyltransferase (UGT) 2A1, and multidrug resistance-related protein type 1] and increased UGT activities. We observed that dexamethasone up-regulated sulfotransferase 1C1 expression in the OM but down-regulated it in the liver. Aroclor and ethoxyquin induced the gene expression of CYP1A and quinone reductase, respectively, in the OM. The transcription factors aryl hydrocarbon receptor, nuclear factor E2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor α, pregnane X receptor, and glucocorticoid receptor were detected in the OM, but no constitutive androstane receptor expression was observed. Dexamethasone and Aroclor enhanced olfactory Nrf2 expression. These results demonstrate that olfactory XME can be modulated by chemicals and that the mechanisms involved in the regulation of these enzymes are tissue-specific.

Mechanisms of olfactory toxicity of the herbicide 2,6-dichlorobenzonitrile: essential roles of CYP2A5 and target-tissue metabolic activation.

The herbicide 2,6-dichlorobenzonitril (DCBN) is a potent and tissue-specific toxicant to the olfactory mucosa (OM). The toxicity of DCBN is mediated by cytochrome P450 (P450)-catalyzed bioactivation; however, it is not known whether target-tissue metabolic activation is essential for toxicity. CYP2A5, expressed abundantly in both liver and OM, was previously found to be one of the P450 enzymes active in DCBN bioactivation in vitro. The aims of this study were to determine the role of CYP2A5 in DCBN toxicity in vivo, by comparing the extents of DCBN toxicity between Cyp2a5-null and wild-type (WT) mice, and to determine whether hepatic microsomal P450 enzymes (including CYP2A5) are essential for the DCBN toxicity, by comparing the extents of DCBN toxicity between liver-Cpr-null (LCN) mice, which have little P450 activity in hepatocytes, and WT mice. We show that the loss of CYP2A5 expression did not alter systemic clearance of DCBN (at 25 mg/kg); but it did inhibit DCBN-induced non-protein thiol depletion and cytotoxicity in the OM. Thus, CYP2A5 plays an essential role in mediating DCBN toxicity in the OM. In contrast to the results seen in the Cyp2a5-null mice, the rates of systemic DCBN clearance were substantially reduced, while the extents of DCBN-induced nasal toxicity were increased, rather than decreased, in the LCN mice, compared to WT mice. Therefore, hepatic P450 enzymes, although essential for DCBN clearance, are not necessary for DCBN-induced OM toxicity. Our findings form the basis for a mechanism-based approach to assessing the potential risks of DCBN nasal toxicity in humans.

[Identification in the rat olfactory epithelium new subgroup YM-1 chitinase-like protein].

Novel protein with a molecular mass of ~43 kDa from rat olfactory epithelium in pathophysiological conditions was discovered. Its amino acid sequence and affiliation with the family 18 glycohydrolase subgroup of chitinase-like proteins YM-1 were determined.

Transient nitric oxide synthase neurons in embryonic cerebral cortical plate, sensory ganglia, and olfactory epithelium.

Neuronal nitric oxide synthase (NOS), visualized immunohistochemically or with NADPH diaphorase histochemistry, is transiently expressed in discrete areas of the developing rat nervous system. In the brain transient NOS expression occurs in the cerebral cortical plate. At E15-E19, the majority of cells in the plate stain, with their processes extending through the corpus striatum to the thalamus. This staining decreases after birth and vanishes by the 15th postnatal day. Neurons in olfactory epithelium also express NOS from E15 till early postnatal life. In embryonic sensory ganglia virtually all neuronal cells are NOS positive, whereas by early adulthood only 1% express NOS. By contrast to these areas of transient NOS expression, in other neuronal sites NOS staining appears after cell bodies cease dividing and cells extend processes, and the staining persists in adult life. The transient expression of neuronal NOS may reflect a role in developmental processes such as programmed cell death.

Odorant stimulation enhances survival of olfactory sensory neurons via MAPK and CREB.

Olfactory sensory neurons (OSNs) can be sensitized to odorants by repeated exposure, suggesting that an animal's responsiveness to olfactory cues can be enhanced at the initial stage of detection. However, because OSNs undergo a regular cycle of apoptosis and replacement by ostensibly naive, precursor-derived neurons, the advantage of sensitization would be lost in the absence of a mechanism for odorant-enhanced survival of OSNs. Using recombinant adenoviruses in conjunction with surgical and electrophysiological techniques, we monitored OSN survival and function in vivo and find that odorant exposure selectively rescues populations of OSNs from apoptosis. We further demonstrate that odorant stimuli rescue OSNs in a cAMP-dependent manner by activating the MAPK/CREB-dependent transcriptional pathway, possibly as a result of expression of Bcl-2.

Electroolfactogram responses from organotypic cultures of the olfactory epithelium from postnatal mice.

Organotypic cultures of the mouse olfactory epithelium connected to the olfactory bulb were obtained with the roller tube technique from postnatal mice aged between 13 and 66 days. To test the functionality of the cultures, we measured electroolfactograms (EOGs) at different days in vitro (DIV), up to 7 DIV, and we compared them with EOGs from identical acute preparations (0 DIV). Average amplitudes of EOG responses to 2 mixtures of various odorants at concentrations of 1 mM or 100 microM decreased in cultures between 2 and 5 DIV compared with 0 DIV. The percentage of responsive cultures was 57%. We also used the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) to trigger the olfactory transduction cascade bypassing odorant receptor activation. Average amplitudes of EOG responses to 500 microM IBMX were not significantly different in cultures up to 6 DIV or 0 DIV, and the average percentage of responsive cultures between 2 and 5 DIV was 72%. The dose-response curve to IBMX measured in cultures up to 7 DIV was similar to that at 0 DIV. Moreover, the percentage of EOG response to IBMX blocked by niflumic acid, a blocker of Ca-activated Cl channels, was not significantly different in cultured or acute preparations.

Pheromone detection in male mice depends on signaling through the type 3 adenylyl cyclase in the main olfactory epithelium.

Terrestrial vertebrates have evolved two anatomically and mechanistically distinct chemosensory structures: the main olfactory epithelium (MOE) and the vomeronasal organ (VNO). Although it has been generally thought that pheromones are detected through the VNO, whereas other chemicals are sensed by the MOE, recent evidence suggests that some pheromones may be detected through the MOE. Odorant receptors in the MOE are coupled to the type 3 adenylyl cyclase (AC3), an enzyme not expressed in the VNO. Consequently, odorants and pheromones do not elicit electrophysiological responses in the MOE of AC3-/- mice, although VNO function is intact. Here we report that AC3-/- mice cannot detect mouse milk, urine, or mouse pheromones. Inter-male aggressiveness and male sexual behaviors are absent in AC3-/- mice. Furthermore, adenylyl cyclase activity in membranes prepared from the MOE of wild-type mice, but not AC3-/- mice, is stimulated by 2-heptanone, a mouse pheromone. We conclude that signaling through AC3 in the MOE is obligatory for male sexual behavior, male-male aggressiveness, and the detection of some pheromones.

Presence of Sex Steroid-Metabolizing Enzymes in the Olfactory Mucosa of Rats.

Although several lines of evidence have suggested that sex steroids influence olfaction, little is known about the cellular basis of steroid-metabolizing enzymes in the olfactory system. Thus, we aimed to examine gene expression and immunolocalization of four sex steroid-metabolizing enzymes in the olfactory mucosa (OM) of albino rats; steroid side chain-cleaving enzyme (P450scc), 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD-1), 17ß-HSD type 2 (17ß-HSD-2), and aromatase. P450scc is known to catalyze conversion from cholesterol to pregnenolone. 17ß-HSD-1 catalyzes conversion from estrone to estradiol, and 17ß-HSD-2 does the reverse. Aromatase catalyzes the conversion from testosterone to estradiol-17ß. Messenger (m) RNAs of all four enzymes mentioned above were detected in the OM. Western blot analysis demonstrated that P450scc, 17ß-HSD-1, and 17ß-HSD-2 were detected in the OM. Immunoreactivity for these three enzymes was observed in sustentacular cells of the olfactory epithelium and acinar cells of Bowman's glands. Immunoelectron microscopy analysis demonstrated immunoreactivity for P450scc in mitochondria, and for 17ß-HSD-1 and 17ß-HSD-2 in the well-developed smooth endoplasmic reticulum and myeloid bodies of the sustentacular cells. The present study suggests that sustentacular cells and acinar cells of the Bowman's glands in the rat OM express at least three of the steroid-metabolizing enzymes, that is, P450scc 17ß-HSD-1, and 17ß-HSD-2, and de novo synthesis of estradiol takes place in the OM. Anat Rec, 300:402-414, 2017. © 2016 Wiley Periodicals, Inc.

Odorant-odorant metabolic interaction, a novel actor in olfactory perception and behavioral responsiveness.

In the nasal olfactory epithelium, olfactory metabolic enzymes ensure odorant clearance from the olfactory receptor environment. This biotransformation of odorants into deactivated polar metabolites is critical to maintaining peripheral sensitivity and perception. Olfactory stimuli consist of complex mixtures of odorants, so binding interactions likely occur at the enzyme level and may impact odor processing. Here, we used the well-described model of mammary pheromone-induced sucking-related behavior in rabbit neonates. It allowed to demonstrate how the presence of different aldehydic odorants efficiently affects the olfactory metabolism of this pheromone (an aldehyde too: 2-methylbut-2-enal). Indeed, according to in vitro and ex vivo measures, this metabolic interaction enhances the pheromone availability in the epithelium. Furthermore, in vivo presentation of the mammary pheromone at subthreshold concentrations efficiently triggers behavioral responsiveness in neonates when the pheromone is in mixture with a metabolic challenger odorant. These findings reveal that the periphery of the olfactory system is the place of metabolic interaction between odorants that may lead, in the context of odor mixture processing, to pertinent signal detection and corresponding behavioral effect.

Uptake and specific binding of 2,3,7,8-tetrachlorodibenzo-p-dioxin in the olfactory mucosa of mice and rats.

Whole-body autoradiography of mice and rats after i.v. administration of 2,3,7,8-[14C]tetrachlorodibenzo-p-dioxin ([14C]TCDD) showed a selective localization of radioactivity in the liver and nasal olfactory mucosa. In microautoradiograms of solvent extracted sections of the skulls of mice given injections of [3H]TCDD, no radioactivity was observed in the olfactory mucosa, suggesting that TCDD is not covalently bound in this tissue. The amount of specific [3H]TCDD binding sites in cytosol from the ethmoturbinates of rats (33 fmol/mg cytosolic protein) was comparable to that of the liver cytosol as estimated by electrophoresis in polyacrylamide concentration gradient gel, and therefore probably too low to explain the retention of radioactivity in the olfactory mucosa. The specific TCDD binding species in the mucosa of the ethmoturbinates exhibited a similar binding affinity for [3H]TCDD, ligand specificity, and molecular weight as the TCDD receptor from rat liver. The 7-ethoxyresorufin O-deethylase activity of the mucosa of the ethmoturbinates was induced less than twice by administration of the TCDD receptor ligand beta-naphthoflavone (5,6-benzoflavone) 40 h before killing. By administration of beta-naphthoflavone (5,6-benzoflavone) 16 h before killing, mRNA coding for cytochrome P-450d but not for cytochrome P-450c was induced to detectable levels in the mucosa of the ethmoturbinal tissue of the rat. The basal activity of 7-ethoxyresorufin O-deethylation of the mucosa of the ethmoturbinates of the rat was comparable to the corresponding activity of the liver. This basal metabolic activity of the ethmoturbinal tissue was only marginally inhibited by antibodies raised against beta-naphthoflavone (5,6-benzoflavone) induced hepatic cytochrome P-450s. Thus, enzymes other than cytochrome P-450c may possibly account for a part of the basal 7-ethoxyresorufin O-deethylase activity in the rodent olfactory mucosa.

Canine olfactory ensheathing cells from the olfactory mucosa can be engineered to produce active chondroitinase ABC.

A multitude of factors must be overcome following spinal cord injury (SCI) in order to achieve clinical improvement in patients. It is thought that by combining promising therapies these diverse factors could be combatted with the aim of producing an overall improvement in function. Chondroitin sulphate proteoglycans (CSPGs) present in the glial scar that forms following SCI present a significant block to axon regeneration. Digestion of CSPGs by chondroitinase ABC (ChABC) leads to axon regeneration, neuronal plasticity and functional improvement in preclinical models of SCI. However, the enzyme activity decays at body temperature within 24-72h, limiting the translational potential of ChABC as a therapy. Olfactory ensheathing cells (OECs) have shown huge promise as a cell transplant therapy in SCI. Their beneficial effects have been demonstrated in multiple small animal SCI models as well as in naturally occurring SCI in canine patients. In the present study, we have genetically modified canine OECs from the mucosa to constitutively produce enzymatically active ChABC. We have developed a lentiviral vector that can deliver a mammalian modified version of the ChABC gene to mammalian cells, including OECs. Enzyme production was quantified using the Morgan-Elson assay that detects the breakdown products of CSPG digestion in cell supernatants. We confirmed our findings by immunolabelling cell supernatant samples using Western blotting. OECs normal cell function was unaffected by genetic modification as demonstrated by normal microscopic morphology and the presence of the low affinity neurotrophin receptor (p75(NGF)) following viral transduction. We have developed the means to allow production of active ChABC in combination with a promising cell transplant therapy for SCI repair.

Pituitary adenylyl cyclase-activating peptides and alpha-amidation in olfactory neurogenesis and neuronal survival in vitro.

We investigated the role of amidated neuropeptides, and specifically pituitary adenylyl cyclase-activating polypeptide (PACAP), in olfactory neurogenesis and olfactory receptor neuronal survival. Using both immunohistochemistry and in situ hybridization, we find that both peptidylglycine alpha-amidating monooxygenase (PAM), the enzyme responsible for amidation and therefore activation of all amidated neuropeptides, and amidated PACAP are expressed in developing and adult olfactory epithelium. Amidated PACAP is highly expressed in proliferative basal cells and in immature olfactory neurons. The PACAP-specific receptor PAC(1) receptor is also expressed in this population, establishing that these cells can be PACAP responsive. Experiments were conducted to determine whether amidated neuropeptides, such as PACAP38, might function in olfactory neurogenesis and neuronal survival. Addition of PACAP38 to olfactory cultures increased the number of neurons to >250% of control and stimulated neuronal proliferation and survival. In primary olfactory cultures, pharmacologically decreased PAM activity, as well as neutralization of PACAP38, caused neuron-specific loss that was reversed by PACAP38. Mottled (Brindled) mice, which lack a functional ATP7A copper transporter and serve as a model for Menkes disease, provided an in vivo partial loss-of-function PAM knock-out. These mice had decreased amidated PACAP production and concomitant decreased numbers of olfactory receptor neurons. These data establish amidated peptides and specifically PACAP as having important roles in proliferation in the olfactory system and suggest that a similar function exists in vivo.

Guanylate cyclase in olfactory cilia from rat and pig.

A guanylate cyclase was identified in cilia from rat and pig olfactory epithelia. Enzyme activities were 200-250 and 90-100 pmol/min.mg-1, respectively. Activity required the presence of non-ionic detergents, e.g., 0.1% Lubrol PX. MnGTP, not MgGTP was used as a substrate. Furthermore, 0.9 mM free Mn2+ was necessary for optimal activity indicating a regulatory site for a divalent cation. The guanylate cyclase displayed sigmoidal Michaelis-Menten kinetics suggesting cooperativity between MnGTP and enzyme. S0.5 was 160 microM MnGTP. The Hill coefficient of 1.7 indicates that more than one class of substrate-binding sites interact in a positive cooperative manner. ATP inhibited the enzyme and linearized plots of substrate kinetics with MnGTP. SH-Blocking agents reversibly inhibited enzyme activity. Sodium azide and nitroprusside were without effect as were several odorants. A guanylate cyclase activity in cilia from tracheal tissue had properties similar to the olfactory enzyme.

High-affinity Ca2+,Mg(2+)-ATPase in plasma membrane-rich preparations from olfactory epithelium of Atlantic salmon.

High-affinity Ca2+,Mg(2+)-ATPase was identified in a plasma membrane-rich fraction of olfactory epithelium from Atlantic salmon (Salmo salar). The enzyme required both Ca2+ and Mg2+ for activation. The apparent Km for Ca2+ was 9.5 nM and Vmax was 0.85 mumol Pi/mg of protein per min. Stimulation by Ca2+ was optimal at 5-100 microM MgCl2. Bovine brain calmodulin had no effect on Ca2+,Mg(2+)-ATPase, even after multiple washes of the membrane preparation with EDTA or EGTA. Endogenous calmodulin was somewhat resistant to removal and could be detected with immunoblotting after multiple washes of the membrane preparation with EDTA or EGTA. This endogenous calmodulin may regulate Ca2+,Mg(2+)-ATPase activity because the activity was inhibited by calmidazolium. Vanadate inhibited Ca2+,Mg(2)-ATPase activity and thapsigargin, a specific inhibitor for Ca2+,Mg(2+)-ATPase of endoplasmic reticulum, had no effect on the enzyme activity. High affinity Ca2+,Mg(2+)-ATPase exists in both ciliary and nonciliary membranes with a similar Km for Ca2+. Ca2+,Mg(2+)-ATPase activity is greater in cilia preparations than in membranes from the deciliated olfactory epithelium. As a putative plasma membrane Ca2+ pump, this high-affinity Ca2+,Mg(2+)-ATPase may play an important role in the regulation of intracellular Ca2+ in olfactory epithelia. In particular, the ciliary membrane may play a prominent role in the removal of Ca2+ from ciliated olfactory receptor cells after odorant stimulation.