Dose-dependent reversal of digoxin-inhibited activity of an in vitro Na+K+ATPase model by digoxin-specific antibody.
We investigated the potency of digoxin-specific Fab fragments to reverse digoxin-induced Na+K+ATPase inhibition in rat brain microsomes according to (a) the extent of initial inhibition of Na+K+ATPase and (b) the neutralizing dose of antibody. Mathematical analysis of the digoxin concentration-Na+K+ATPase inhibition curve supports the existence of 2 digoxin sensitive Na+K+ATPase isoforms. The IC50 was 1.3 x 10(-4) M and 2.5 x 10(-8) M for the low (alpha 1) and high (alpha 2) digoxin affinity isoenzyme, respectively. The reversal of digoxin-induced Na+K+ATPase inhibition was dependent on the digoxin-specific Fab concentration. The maximal effect was observed when the Fab:digoxin ratio was stoichiometrical and addition of an excess of antibodies did not result in a complete reversal of inhibition at the 4 digoxin concentrations studied. This simple and rapid in vitro model will be a useful tool to predict the efficacy of a new generation of antibodies.
Cano
N J
NJ
INSERM U26 Hôpital Fernand Widal, Paris, France.
Sabouraud
A E
AE
Debray
M
M
Scherrmann
J M
JM
D000818:Animals; D000937:Antigen-Antibody Reactions; D001921:Brain / Q000201:enzymology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004077:Digoxin / Q000276:immunology* / Q000494:pharmacology*; D004306:Dose-Response Relationship, Immunologic; D007140:Immunoglobulin Fab Fragments / Q000276:immunology / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D008861:Microsomes / Q000201:enzymology; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*
D007140:Immunoglobulin Fab Fragments; D004077:Digoxin; D000254:Sodium-Potassium-Exchanging ATPase