ABSTRACT
1 We studied the pharmacological properties of native rat brain and heterologously expressed rat alpha4beta2 nicotinic receptors immunoprecipitated onto a fixed substrate with the anti-alpha4 antibody mAb 299. 2 Immunodepletion with the anti-beta2 antibody mAb 270 showed that 89% of the mAb-299-precipitated rat brain receptors contained beta2. 3 The association and dissociation rate constants for 30 pM +/-[3H]-epibatidine binding to alpha4beta2 receptors expressed in oocytes were 0.02+/-0.01 and 0.03+/-0.01 min-1 (+/-standard error, degrees of freedom=7 - 8) at 20 - 23 degrees C. 4 The Hill coefficients for +/-[3H]epibatidine binding to the native brain, alpha4beta2 receptors expressed in oocytes, and alpha4beta2 receptors expressed in CV-1 cells (using recombinant adenovirus) were 0.69 - 0.70 suggesting a heterogeneous receptor population. Fits of the +/-[3H]-epibatidine concentration-binding data to a two-site model gave KD s of 8 - 30 and 560 - 1,200 pM. The high-affinity sites comprised 73 - 74% of the native brain and oocyte alpha4beta2 receptor population, 85% of the CV-1 alpha4beta2 receptor population. 5 The expression of rat alpha4beta2 receptors in CV-1 cells using vaccinia viral infection-transfection resulted in a more homogeneous receptor population (Hill coefficient of 1. 0+/-0.2). Fits of the +/-[3H]-epibatidine binding data to a single-site model gave a KD of 40+/-3 pM. 6 DHbetaE (IC50=260-470 nM) and the novel nicotine analogue NDNI (IC50=7-10 microM) inhibited 30 pM+/-[3H]-epibatidine binding to the native brain and heterologously expressed alpha4beta2 receptors equally well. 7 The results show that alpha4beta2-containing nicotinic receptors in the rat brain and heterologously expressed rat alpha4beta2 receptors have similar affinities for +/-[3H]-epibatidine, DHbetaE, and NDNI.
Subject(s)
Brain/metabolism , Receptors, Nicotinic/metabolism , Animals , Antibodies, Monoclonal/immunology , Antibodies, Monoclonal/metabolism , Binding, Competitive/drug effects , Bridged Bicyclo Compounds, Heterocyclic/metabolism , Bridged Bicyclo Compounds, Heterocyclic/pharmacology , Cell Line , Dihydro-beta-Erythroidine/metabolism , Dihydro-beta-Erythroidine/pharmacology , Female , Gene Expression , Humans , Kinetics , Nicotine/analogs & derivatives , Nicotine/pharmacology , Oocytes/cytology , Oocytes/metabolism , Precipitin Tests , Pyridines/metabolism , Pyridines/pharmacology , Rats , Receptors, Nicotinic/genetics , Receptors, Nicotinic/immunology , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Tritium , XenopusABSTRACT
Wavelength and temperature-dependent characteristics of silicon reach-through avalanche photodiodes (RAPD) are studied using the modified Baraff's theory. The temperature and wavelength regions discussed are 100-500 K and 0.655-1.06 microm, respectively, for Si photodetectors. The effects of breakdown voltage, depletion region width, and efficiency on the avalanche region width are widely studied. Both n(+) (front) side and p(+) (back) side illumination are also considered. The noise equivalent power is significantly reduced with light incident on the p(+) surface with little sacrifice of efficiency. An RAPD structure is proposed in which the direction of radiation incidence causes photogeneration to precede avalanche multiplication reducing the multiplication noise substantially. This result should be useful in the design of RAPD laser detectors.
