Regulation of Ca2+ signaling by Na+ pump alpha-2 subunit expression.
The role of the Na(+) pump alpha2 subunit in Ca(2+) signaling was examined in primary cultured astrocytes from wild type (WT) mouse fetuses and those with a null mutation in one (Het) or both (KO) alpha2 genes. Cytosol Na(+) and Ca(2+) concentrations ([Na(+)](CYT) and [Ca(2+)](CYT)) were measured with benzofuran isophthalate (SBFI) and Fura-2. Het astrocytes express approximately 50% of normal alpha2; KO cells express none. Resting [Na(+)](CYT) = 6.5 mM in WT, 6.8 mM in Het, and 8.0 mM in KO cells; 500 nM ouabain (which inhibits only alpha2) equalized [Na(+)](CYT) at 8 mM in all genotypes. Resting [Ca(2+)](CYT) = 132 nM in WT, 162 nM in Het and 196 nM in KO cells. Cyclopiazonic acid (CPA), which inhibits endoplasmic reticulum (ER) Ca(2+) pumps, induces elevation of [Ca(2+)]CYT. These Ca(2+) responses are augmented in Het and KO cells. This correlates with alpha2 Na(+) pump and Na(+)/Ca(2+) exchanger (NCX) localization in plasma membrane (PM) microdomains that overlie the ER. Selective reduction of alpha2 Na(+) pump activity apparently elevates local [Na(+)] and, via NCX, [Ca(2+)] in the tiny cytosolic space between the PM and ER. This augments adjacent ER Ca(2+) stores and amplifies Ca(2+) signaling without elevating bulk [Na(+)](CYT).
Golovina
Vera
V
Department of Physiology, University of Maryland School of Medicine, Baltimore 21201, USA. vgolovin@umaryland.edu
Song
Hong
H
James
Paul
P
Lingrel
Jerry
J
Blaustein
Mordecai
M
D000818:Animals; D001253:Astrocytes / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D003600:Cytosol / Q000201:enzymology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D018345:Mice, Knockout; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000172:deficiency / Q000235:genetics / Q000502:physiology*
D004791:Enzyme Inhibitors; D007211:Indoles; D012964:Sodium; C401838:Atp1a2 protein, mouse; D000254:Sodium-Potassium-Exchanging ATPase; C000543:cyclopiazonic acid