Receptor cell responses

The specificity of an olfactory cell reflects the specificity of membrane receptors, also called acceptors, which are assumed to be located in the dendritic membranes. The possibility that the specificity might be confined to the conduction system, e.g., microtubules, was excluded by the observation that two sensory cells innervating the same sensillum, and sharing the same conduction system, could be activated by different key substances. In activating a cell, the odor molecule is thought to bind to a membrane receptor protein 

The number of s. trichodea sensory cells varies from one to five, depending on the lepidopteran species (Priesner, 1979a). In some species the cell generating the largest spike amplitude in each sensillum consistently belong to the same cell type, i.e. maximally responds to the same key substance, which is the 

It is difficult to compare the absolute sensitivities of the pheromone cells of bark beetles and moths on the basis of available experimental results, because different stimulation techniques have been used, and because the two classes of compounds have different vapor pressures. However, with cartridge-techniques, 

Recordings of olfactory receptor cells in Scolytus multistriatus and S. scolytus revealed the same degree of specialization as that found for Ips species. In males of S. multistriatus (attracted to the three-component mixture, multilure) the majority of receptor cells were keyed to either of the two compounds produced by females, (- )-a-multistriatin and (- )-threo-4-methyl-3-heptanol (Angst, 1981). 

However, no cells in the males were keyed to the third compound (- )-cubebene which is produced by the host tree. Both sexes of 5. scolytus possess a majority of receptor cells keyed to either of the two male-produced compounds, (-)-threo-4-methyl-3-heptanol and the (-)-erythro-stereo-isomer, and in this species some cells were keyed also to (- )- -multistriatin (Wadhams et al., 1982). The relative sensitivities and specificities of these cells were determined in the same way as described for Ips species. Each cell was minimally activated by pheromone components other than its own key substance. The functional types of olfactory receptor cells discussed here for Scolytus, as with the cells of Ips, apparently are all keyed to the specific isomer of the pheromone compounds. The cells specialized to (- )-a-multistriatin are 1000 times less sensitive to the geometrical isomer d-multistriatin. However, the discrimination of the optical form of multistriatin seemed to be less pronounced. The substantially lower effect of the (-l-)-stereo-isomer (optical purity 99.5%), cannot be solely ascribed to contamination with the (- )-enantiomer. It implies that these cells in fact may also respond to (-l- )-multistriatin, although to a lesser extent. The cells keyed to methyl-heptanol are, however, highly optically specific in both species. 

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Kaissling K.-E. (1986) Temporal characteristics of pheromone receptor cell responses in relation to orientation behaviour of moths. In Mechanisms in Insect Olfaction, eds T. L. Payne, M. C. Birch and C. E. J. Kennedy, pp. 193-199. Oxford University Press, New York. 

G. Sicard and A. Holley, Receptor cell responses to odorants similarities and differences among odorants. Brain Res. 292 (1984) 283-96. 

ASCOLICHRISTENSEN, A., SALOM, S.M., PAYNE, T.L., Olfactory receptor cell responses of Ips grandicollis (Eichhoff) (Coleoptera Scolytidae) to intraspecific and interspecific behavioral chemicals, J Chem. Ecol, 1993,19, 699-712. 

DIEHL, P.A., VLIMANT, M., GUERENSTEIN, P., GUERIN, P.M., Ultrastructure and receptor cell responses of the antennal grooved peg sensilla of Triatomainfestans (Hmiptera Reduviidae), Arthropod Structure and Development, 2003, 31, 271-285. 

Debruyne, M. and P. M. Guerin, Isolation of 2,6-dichlorophenol from the cattle tick Boophilus microplus Receptor cell responses but no evidence for a behavioral response. J Insect Physiol, 1994. 40(2) 143-154. 

Researchers at the MoneU Center (Philadelphia, Pennsylvania) are using a variety of electrophysical and biochemical techniques to characterize the ionic currents produced in taste and olfactory receptor cells by chemical stimuli. These studies are concerned with the identification and pharmacology of the active ion channels and mode of production. One of the techniques employed by the MoneU researchers is that of "patch clamp." This method aUows for the study of the electrical properties of smaU patches of the ceU membrane. The program at MoneU has determined that odors stimulate intraceUular enzymes to produce cycUc adenosine 3, 5 -monophosphate (cAMP). This production of cAMP promotes opening of the ion channel, aUowing cations to enter and excite the ceU. MoneU s future studies wiU focus on the connection of cAMP, and the production of the electrical response to the brain. The patch clamp technique also may be a method to study the specificity of receptor ceUs to different odors, as weU as the adaptation to prolonged stimulation (3). 

Secondly, treatment of neutrophils with pertussis toxin, which ADP-ribosylates a neutrophil G protein and causes a loss of cell responsiveness via receptor-mediated pathways (40,41), has minimal effect on the response to HCH (Figure 11, lower panel). Thus it can be concluded that HCH activation of neutrophils is independent of receptor-mediated activation of G proteins. 

G Protein Families. Cell responses to the binding of stimulatory ligands (L) to cell-surface receptors (R) proceed through a multistep... 

A few seconds after the addition of the inhibitor, cell responses begin to decay (see Figure 8, Omann and Sklar, this volume). Six cell responses have been characterized in this manner (2i). Because the slowly dissociating receptor state (Figure 2) is found on cells at a time when cell responses have ceased, we suggested that this state was inactive the rapidly dissociating state could be associated with cell activation. 

The model predicts the behavior of the active state LRG to be analogous to cell activation itself. LRG rises in seconds, disappears in minutes as binding equilibrates, and, when binding is interrupted, disappears in a few seconds as this state disappears, transduction also "collapses" and cell responses decay. The model should not be viewed as complete, however. For example, amplification steps, which permit the activation of multiple G proteins by a single receptor, would be built into the model by adding a reverse rate from LR to LRG. Such amplification would have to be verified experimentally. 

These methods, when combined with real-time analysis of cell response (Omann and Sklar, this volume), also permit a quantitative analysis of the relationship between receptor occupancy and cell response. 

Bansal G, DiVietro JA, Kuehn HS, Rao S, Nocka KH, Gilfillan AM, Druey KM RGS13 controls G protein-coupled receptor-evoked responses of 56 human mast cells. J Immunol 2008 181 7882-7890. 

Lasareff put forward a chemical theory in which each receptor was responsive to only a single taste, and that applied stimuli caused the decomposition of a material within the cell. This decomposition produced ions which then excited the nerve endings in the papillae, the concentration of the ionized products determining the magnitude of the neural activity. 

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