EN
A possible role of serine/threonine protein phosphatases PP1 and PP2A in the regulation in vitro of the plasma membrane Ca2+-ATPase purified from rat cortical and cerebellar synaptosomal membranes was investigated. Calcium pump, the enzyme responsible for the maintenance of intracellular calcium homeostasis, is regulated by several mechanisms, including phosphorylation by protein kinases. Here we demonstrate that the protein phosphatases action decreased the activity of native Ca2+-ATPase, and increased the stimulatory effect of calmodulin. Moreover, the calcium pump dephosphorylated by PP1 and PP2A revealed the presence of the additional sites, accessible for a PKA-mediated phosphorylation. The subsequent PKA or PKC phosphorylation of the dephosphorylated cortical and cerebellar Ca2+-ATPase differentially regulated its hydrolytic activity. This study confirms that Ca2+-ATPase in nervous cell is phosphorylated in vivo, and shows for the first time that its activity may be directly regulated by PP1 and PP2A.