ADENYLYL CYCLASES - MESSENGER-RNA AND CHARACTERISTICS OF ENZYME-ACTIVITY IN 3 AREAS OF BRAIN

RNase protection assays were used in a comparative analysis of the qua ntities of mRNA for five ''calcium-sensitive'' (types I, III, V, VI, a nd VIII) adenylyl cyclases and one ''calcium-insensitive'' (type II) a denylyl cyclase in mouse cerebral cortex, cerebellum, and nucleus accu mbens. The mRNA levels for type V adenylyl cyclase were dominant in th e nucleus accumbens, Type V adenylyl cyclase mRNA was also found in th e cerebral cortex and at low levels in the cerebellum, Type I adenylyl cyclase mRNA was the major form in the cerebellum with 15-50-fold hig her levels compared with other adenylyl cyclase mRNAs, Type I adenylyl cyclase mRNA was also the most prominent adenylyl cyclase mRNA in the cerebral cortex, although the mRNA levels of other adenylyl cyclase f orms were more comparable to those of the type I enzyme in this brain area, The mRNA levels for adenylyl cyclase types II, III, VI, and VIII were intermediate to low depending on the brain area. Cell membranes from the nucleus accumbens demonstrated adenylyl cyclase activity that was synergistically activated by concomitant addition of GTP and fors kolin to assay mixtures, reflecting a characteristic of type V adenyly l cyclase protein. Calcium/calmodulin stimulated adenylyl cyclase acti vity in membranes from all three brain areas, However, synergistic act ivation of adenylyl cyclase activity by GTP and calcium/calmodulin was noted only with cortical membranes, and this characteristic may refle ct the presence of type VIII adenylyl cyclase mRNA in the cortex, Alth ough mRNA for type VIII adenylyl cyclase was almost equivalent in the cortex and cerebellum, the lack of a synergistic effect of GTP plus ca lcium/calmodulin on the cerebellar enzyme activity may be a result of the significant dominance of type I adenylyl cyclase mRNA (and protein ) in the cerebellum, In general, the mRNA levels for the various adeny lyl cyclases were predictive of the regulatory characteristics of aden ylyl cyclase activity in membranes of the brain areas studied.