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

Abstract: The effects of dibutyryl cyclic AMP (dbcAMP) and dibutyryl cyclic GMP (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 to 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. These findings suggest that the Mg²⁺‐independent, Ca²⁺‐ATPase activity in rat brain is regulated by a cyclic GMP‐dependent process. Further, the data provide evidence that the Ca²⁺‐ATPase activity in lysed synaptosomal membranes represents an enzyme that is distinguishable from both the Mg²⁺‐ and (Ca²⁺+ Mg²⁺‐ATPase.