Molecular interactions of the plasma membrane calcium ATPase 2 at pre- and post-synaptic sites in rat cerebellum.

The plasma membrane calcium extrusion mechanism, PMCA (plasma membrane calcium ATPase) isoform 2 is richly expressed in the brain and particularly the cerebellum. Whilst PMCA2 is known to interact with a variety of proteins to participate in important signalling events [Strehler EE, Filoteo AG, Penniston JT, Caride AJ (2007) Plasma-membrane Ca(2+) pumps: structural diversity as the basis for functional versatility. Biochem Soc Trans 35 (Pt 5):919-922], its molecular interactions in brain synapse tissue are not well understood. An initial proteomics screen and a biochemical fractionation approach identified PMCA2 and potential partners at both pre- and post-synaptic sites in synapse-enriched brain tissue from rat. Reciprocal immunoprecipitation and GST pull-down approaches confirmed that PMCA2 interacts with the post-synaptic proteins PSD95 and the NMDA glutamate receptor subunits NR1 and NR2a, via its C-terminal PDZ (PSD95/Dlg/ZO-1) binding domain. Since PSD95 is a well-known partner for the NMDA receptor this raises the exciting possibility that all three interactions occur within the same post-synaptic signalling complex. At the pre-synapse, where PMCA2 was present in the pre-synapse web, reciprocal immunoprecipitation and GST pull-down approaches identified the pre-synaptic membrane protein syntaxin-1A, a member of the SNARE complex, as a potential partner for PMCA2. Both PSD95-PMCA2 and syntaxin-1A-PMCA2 interactions were also detected in the molecular and granule cell layers of rat cerebellar sagittal slices by immunohistochemistry. These specific molecular interactions at cerebellar synapses may allow PMCA2 to closely control local calcium dynamics as part of pre- and post-synaptic signalling complexes

Measurement of plasma membrane calcium-calmodulin-dependent ATPase (PMCA) activity.

The plasma membrane calcium-calmodulin-dependent ATPase (PMCA) is a calcium-extruding enzymatic pump that ejects calcium from the cytoplasm to the extracellular compartment. Although in excitable cells such as skeletal and cardiac muscle cells PMCA has been shown to play only a minor role in regulating global intracellular calcium concentration, increasing evidence points to an important role for PMCA in signal transduction, in particular in the nitric oxide signaling pathway. Moreover, recent evidence has shown the functional importance of PMCA in mediating cardiac contractility and vascular tone. Here we describe a method in determining PMCA activity in the microsomal membrane preparation from cultured cells that overexpress specific isoform of PMCA by using modified coupled enzyme assay