Dibutyryl-Cyclic GMP Stimulation of Ca2+-ATPase Activity in Rat Brain Synaptic Membranes

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Abstract
The effects of dibutyryl cAMP (db-cAMP) and dibutyryl cGMP (db-cGMP) were tested on Ca2+-ATPase, Mg2+-ATPase, and (Ca2+ + Mg2+)-ATPase activities in lysed synaptosomes prepared from whole rat brains (minus cerebellum). At concentrations from 0.1-2.0 mM, db-cGMP produced a selective, concentration-dependent increase in Ca2+-ATPase activity. Both db-cGMP and db-cAMP slightly reduced Mg2+-ATPase activity, whereas neither compound had concentration-dependent effects on (Ca2+ + Mg2+)-ATPase activity. The Mg2+-independent, Ca2+-ATPase activity in rat brain apparently is regulated by a cGMP-dependent process. The Ca2+-ATPase activity in lysed synaptosomal membranes represents an enzyme that is distinguishable from both the Mg2+- and (Ca2+ + Mg2+) ATPase.