Radiation inactivation of alpha 1-adrenoceptors in rat cerebral cortex membranes has been performed with 10 MeV electrons from a linear accelerator at temperatures less than or equal to -100 degrees C. Alpha 1-adrenoceptor inactivation was monitored with [ 3H ]-prazosin and [( 125I ]-2-(beta-4-hydroxylphenyl)ethylaminomethyl)tetralone [( 125I ]-HEAT). Saturation analysis of irradiated membranes with both ligands indicated that a decrease in alpha-adrenoceptor density occurred with increasing radiation dose. The dissociation constants of [ 3H ]-prazosin and [ 125I ]-HEAT were not markedly changed by the irradiation. Application of the target volume theory gave molecular weights of 91,500 +/- 1,700 (S.D.) (D37: 19,6 +/- 0.36 Mrad) with [ 125I ]-HEAT as ligand, and 77,000 +/- 18,000 (S.D.) (D37: 23.3 +/- 4.6 Mrad) with [ 3H ]-prazosin, respectively, when an empirical temperature correction factor of 2.8 was used. [ 3H ]-flunitrazepam-labelled benzodiazepine receptor target size was used as an internal control. The molecular weight of the alpha 1-adrenoceptors, corrected for this internal control, was 85,000 +/- 1.600 [( 125I ]-HEAT) and 71,500 +/- 17,000 [( 3H ]-prazosin).
With the presently available equipment (Coulter counter in combination with a multichannel analyzer) reproducible and biologically meaningfull cell volume distributions can be recorded within a short time (2–3 min) from a large sample of cells (105). Lymph cells remain nearly stable for 2–3 hours in lymph with heparin as anticoagulant. On dilution with most of the presently available ‘isotonic’ and ‘balanced’ salt solutions the lymph cells immediately start to swell or shrink. In two diluents a labile equilibrium of volume distribution is maintained for about 10 min. During this time a reproducible size distribution diagram can be recorded. Some potentialities and limitations of the method are discussed on the basis of two experiments: the changes in size distribution of cells in the efferent lymph of an antigenically stimulated lymph node and in thoracic duct lymph in the course of a depletion of the pool of recirculating lymphocytes.
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