Extracellular terbium and divalent cation effects on the red blood cell Na pump and chrysoidine effects on the renal Na pump.
We examined the effect of extracellular terbium (Tb(3+)) and divalent metal cations (Ca(2+), Sr(2+), and Ba(2+)) on (86)Rb(+) influx into rabbit and human red blood cells. We found that Tb(3+) at 15 and 25 microM was a non-competitive inhibitor of (86)Rb(+) influx suggesting that Tb(3+) is not binding to the transport site. This result reduces the usefulness of Tb(3+) as a potential probe for the E(out) conformation (the conformation with the transport site facing extracellularly). Ba(2+), Sr(2+) and Ca(2+), at concentrations >50 mM, had minimal effects on Rb(+) influx into red blood cells (1 mM Rb-out). This suggests that the outside transport site is very specific for monovalent cations over divalent cations, in contrast to the inside transport site. We also found that chrysoidine (4-phenylazo-m-phenylenediamine) competes with Na(+) for ATPase activity and K(+) for pNPPase activity suggesting it is binding to the E(in) conformation. Chrysoidine and similar compounds may be useful as optical probes of the E(in) conformation.
Reifenberger
Matthew S
MS
Department of Medical Pharmacology and Physiology, School of Medicine, Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, USA.
Arnett
Krista L
KL
Gatto
Craig
C
Milanick
Mark A
MA
D009597:4-Nitrophenylphosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D002413:Cations, Divalent / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004912:Erythrocytes / Q000166:cytology / Q000201:enzymology*; D006801:Humans; D017136:Ion Transport / Q000187:drug effects; D007668:Kidney / Q000201:enzymology*; D011817:Rabbits; D012756:Sheep; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013725:Terbium / Q000494:pharmacology*; D010128:p-Aminoazobenzene / Q000031:analogs & derivatives* / Q000494:pharmacology
D002413:Cations, Divalent; D013725:Terbium; C005562:chrysoidine; D010128:p-Aminoazobenzene; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase