title: Properties of a 3H-adenine prelabeled vesicular preparation from guinea pig cerebral cortex. Optimization of incubation conditions for basal- and histamine-stimulated 3H-cyclic AMP levels.
abstract: The effects of several variables related to incubation conditions were studied on both the basal and the histamine-stimulated 3H-cyclic AMP levels in a 3H-adenine prelabeled vesicular preparation of guinea pig cerebral cortex. Varying the preincubation time (i.e., the duration of incubation before labeling) caused pronounced differences in the postlabeling time course of 3H-cyclic AMP levels. A preincubation time of 45 min was found to minimize time-related postlabeling declines in 3H-cyclic AMP basal activity. Labeling of the homogenate for an entire experiment in one vessel ("bulk labeling") also contributed to time-related declines in activity; these changes were minimized by labeling aliquots of homogenate individually. Rapid sample mixing during incubation was found to be necessary to ensure adequate suspension of the preparation and to achieve a stable basal activity. Such mixing altered the pH of the samples; maintenance of the pH at 7.4 required a decrease in the bicarbonate concentration and/or use of supplementary buffers. Several parameters related to histamine concentration-response curves were found to be affected by various combinations of buffers and labeling methods. Individual labeling in Krebs-ringer-bicarbonate (15 mM) buffer gave the most stable and reproducible responses to histamine. This method permits detailed pharmacological characterization of transmitter-stimulated cyclic AMP changes in a cell-free system that retains many characteristics of brain slices.
mesh_terms: D000225:Adenine / Q000378:metabolism*; D000818:Animals; D002540:Cerebral Cortex / Q000032:analysis*; D000242:Cyclic AMP / Q000032:analysis* / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D006632:Histamine / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008297:Male; D013997:Time Factors; D014316:Tritium
chemical_list: D014316:Tritium; D006632:Histamine; D000242:Cyclic AMP; D000225:Adenine