Logarithmic receptors

For an electronic realization of their system, Land and McCann suggest using logarithmic receptors. If logarithmic receptors are used, then the sequential product turns into a sum. Let log aj be the measured data from the j-th receptor of color band i with i e r, g, h) along the path. Then the ratio between two adjacent receptors can be computed using a simple subtraction. 

Figure 7.5 Schematic diagram of Land and McCann s prototype (a). Logarithmic receptors are spaced equidistant along a path. The output of two adjacent receptors A and B is added at point C. Because the first term is added with a negative voltage, the ratio of reflectances between A and B is computed at C. At point E the existing sequential product D is added to the result from C. The black square denotes that the sequential product is set to zero if it becomes larger than zero. The reflectances are read out at point F. A circuit for two adjacent receptors A and B is shown in (b). A light bulb (F) is used to visualize the reflectances (Reproduced from Land EH and McCann JJ 1971 Lightness and retinex theory. Journal of the Optical Society of America, 61(1), 1-11 by permission from The Optical Society of America).

The dissociation content for the competitive antagonist, iCg, can be deterrnined without knowing the relationship between receptor occupancy and response. Equation 17 is often written in logarithmic form ... 

FIGURE 3.12 Dependence of constitutive receptor activity as ordinates (expressed as a percent of the maximal response to a full agonist for each receptor) versus magnitude of receptor expression (expressed as the amount of human cDNA used for transient transfection, logarithmic scale) in Xenopus laevis melanophores. Data shown for human chemokine CCR5 receptors (open circles), chemokine CXCR receptors (filled triangles), neuropeptide Y type 1 receptors (filled diamonds), neuropeptide Y type 2 receptors (open squares), and neuropeptide Y type 4 receptors (open inverted triangles). Data recalculated and redrawn from [27],... 

FIGURE 4.13 Effect of the allosteric modulator 5-(N-ethyl-N-isopropyl)-amyloride (EPA) on the kinetics dissociation of [3H] yohimbine from c/j-adrenoceptors, (a) Receptor occupancy of [3H] yohimbine with time in the absence (filled circles) and presence (open circles) of EPA 0.03 mM, 0.1 mM (filled triangles), 0.3 mM (open squares), 1 mM (filled squares), and 3 mM (open triangles), (b) Regression of observed rate constant for offset of concentration of [3H] yohimbine in the presence of various concentrations of EPA on concentrations of EPA (abscissae in mM on a logarithmic scale). Data redrawn from [13]. 

FIGURE 5.10 Effects of co-expressed G-protein (G ) on neuropeptide NPY4 receptor responses (NPY-4). (a) Dose-response curves for NPY-4. Ordinates Xenopus laevis melanophore responses (increases light transmission). Ordinates logarithms of molar concentrations of neuropeptide Y peptide agonist PYY. Curves obtained after no co-transfection (labeled 0 jig) and co-transfection with cDNA for Gai6. Numbers next to the curves indicate jig of cDNA of Ga]g used for co-transfection, (b) Maximal response to neuropeptide Y (filled circles) and constitutive activity (open circles) as a function of pg cDNA of co-transfected G g. 

Figure 17.8 Comparison of the antagonist potencies of some neuroleptics on different NT receptors. Data are shown for haloperidol (HAL), chlorpromazine (CPZ), clozapine (CLOZ) and risperidone (RISP) acting on dopamine Dj and D2, 5-HT2 (S2), alpha (0(2) adrenoceptors and cholinergic muscarinic receptors (M). The height of each column shows an average of the dissociation constants obtained from a number of publications (see Seeman 1990). The values, which can vary some fiftyfold, are expressed as the negative logarithms (i.e. 9 = 10 M,lnM) so that the higher the column, the more potent the compound. The order of potency of the four compounds at each receptor is shown alongside...

The spectral map shows three distinct poles of specificity. These are respectively the p-receptor (DHM), the 6-receptor (DADLE) and the K-receptor (EKC). The naloxone receptor (NAL) appears to be strongly correlated with the p-receptor (DHM) and, hence, provides little additional information. In spectral map analysis, correlation between variables, as well as similarity between compounds, is evidenced by the proximity of their corresponding symbols. The lines drawn through the three poles of the map represent bipolar axes of contrast. A contrast is defined in this context as a log ratio or, equivalently, as a difference of logarithms. For example, the horizontal axis through the p- and 8-receptors defines the p/6 contrast. Compounds that project on the right side of this axis bind more specifically to the p-receptor, while those that project on the left side possess more... 

Negative logarithm of ionization constant Ka Polar surface area Pregnane X receptor... 

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