Plasma membrane-cytoskeleton-endoplasmic reticulum complexes in neurons and astrocytes.
The possibility that certain integral plasma membrane (PM) proteins involved in Ca(2+) homeostasis form junctional units with adjacent endoplasmic reticulum (ER) in neurons and glia was explored using immunoprecipitation and immunocytochemistry. Rat brain membranes were solubilized with the mild, non-ionic detergent, IGEPAL CA-630. Na(+)/Ca(2+) exchanger type 1 (NCX1), a key PM Ca(2+) transporter, was immunoprecipitated from the detergent-soluble fraction. Several abundant PM proteins co-immunoprecipitated with NCX1, including the alpha2 and alpha3 isoforms of the Na(+) pump catalytic (alpha) subunit, and the alpha2 subunit of the dihydropyridine receptor. The adaptor protein, ankyrin 2 (Ank 2), and the cytoskeletal proteins, alpha-fodrin and beta-spectrin, also selectively co-immunoprecipitated with NCX1, as did the ER proteins, Ca(2+) pump type 2 (SERCA 2), and inositol-trisphosphate receptor type 1 (IP(3)R-1). In contrast, a number of other abundant PMs, adaptors, and cytoskeletal proteins did not co-immunoprecipitate with NCX1, including the Na(+) pump alpha1 isoform, PM Ca(2+) pump type 1 (PMCA1), beta-fodrin, and Ank 3. In reciprocal experiments, immunoprecipitation with antibodies to the Na(+) pump alpha2 and alpha3 isoforms, but not alpha1, co-immunoprecipitated NCX1; the antibodies to alpha1 did, however, co-immunoprecipitate PMCA1. Antibodies to Ank 2, alpha-fodrin, beta-spectrin and IP(3)R-1 all co-immunoprecipitated NCX1. Immunocytochemistry revealed partial co-localization of beta-spectrin with NCX1, Na(+) pump alpha3, and IP(3)R-1 in neurons and of alpha-fodrin with NCX1 and SERCA2 in astrocytes. The data support the idea that in neurons and glia PM microdomains containing NCX1 and Na(+) pumps with alpha2 or alpha3 subunits form Ca(2+) signaling complexes with underlying ER containing SERCA2 and IP(3)R-1. These PM and ER components appear to be linked through the cytoskeletal spectrin network, to which they are probably tethered by Ank 2.
Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
Lubomira
L
Lencesova
Andrea
A
O'Neill
Wendy G
WG
Resneck
Robert J
RJ
Bloch
Mordecai P
MP
Blaustein
D000818:Animals; D017487:Ankyrins / Q000378:metabolism; D001253:Astrocytes / Q000378:metabolism* / Q000648:ultrastructure; D020013:Calcium Signaling; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D003599:Cytoskeleton / Q000378:metabolism* / Q000648:ultrastructure; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism* / Q000648:ultrastructure; D021381:Protein Transport; D051381:Rats; D017207:Rats, Sprague-Dawley; D013049:Spectrin / Q000378:metabolism
D017487:Ankyrins; D008565:Membrane Proteins; D013049:Spectrin