Influence of plasma membrane depolarization on cAMP level in rat brain synaptosomes

We studied the influence of plasma membrane depolarization on cAMP content in presynaptic nerve endings (synaptosomes) isolated from brain hemispheres (HS) and cerebellum (CS). Depolarization by elevated [K+]o decreased basal cAMP level in both types of synaptosomes; reduced cAMP content in HS and increased cAMP in CS in the presence of IBMX; and lowered forskolin-stimulated cAMP accumulation in both the HS and the CS. Similar results were obtained when depolarization was induced by veratrine or when [Ca2+]i was elevated by treatment of the synaptosomes with the ionophore A23187. In Ca2+-free media, depolarization was not able to affect the synaptosomal cAMP levels. These data suggest that in brain synaptosomes intracellular cAMP pathway is modulated by alterations in [Ca2+]i.