Effect of growth in low-Na+ medium on transport sites in cultured heart cells.
Increases in intracellular Na+ concentration ([Na+]i) lead to an increase in the number of Na+ pump sites in the cell membrane. To investigate further the role of [Na+]i in the regulation of Na+-K+-ATPase sites, we studied the effect of reduced [Na+]i on the number of Na+ pump sites and Na+-K+ pump activity using spontaneously beating cultured chick ventricular cells. Cells incubated in medium containing 60, 80, 100, or 140 mM Na+ for 24 or 48 h showed an extracellular [Na+]-dependent alteration in cellular Na+ content. The number of Na+ pump sites identified by [3H]ouabain binding binding declined with decreasing levels of Na+ in the medium in a time-dependent manner over 48 h, with a concomitant increase in cellular Na+ content. Verapamil (1 microM) or tetrodotoxin (1 microM) significantly reduced cellular Na+ content by 30 min of exposure and the number of Na+ pump sites by 48 h of incubation. Na+ pump activity determined from the ouabain-sensitive 42K+ uptake rate was significantly reduced in cells grown in low Na+ for 48 h, as was pump capacity, determined in Na+-loaded cells. These results support the view that [Na+]i exerts a long-term modulating effect on the number of physiologically functional Na+ pump sites.
D000818:Animals; D001693:Biological Transport, Active; D002452:Cell Count; D002455:Cell Division; D002478:Cells, Cultured; D002642:Chick Embryo; D003470:Culture Media; D007700:Kinetics; D009200:Myocardial Contraction; D009206:Myocardium / Q000166:cytology*; D010042:Ouabain / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D014700:Verapamil / Q000494:pharmacology
D003470:Culture Media; D013779:Tetrodotoxin; D010042:Ouabain; D012964:Sodium; D014700:Verapamil; D011188:Potassium