Selective inhibition of [3H]nitrendipine binding to brain and cardiac membranes by bacitracin.
The effects of bacitracin were investigated on [3H]nitrendipine binding to rat brain and cardiac membranes in a low ionic strength (5 mM Tris-HCl) buffer. Bacitracin inhibited [3H]nitrendipine binding to rat brain and cardiac membranes with IC50 values of 400 +/- 100 and 4600 +/- 400 micrograms/mL, respectively. Scatchard analysis in brain membranes revealed that bacitracin inhibited [3H]nitrendipine binding primarily by reducing the Bmax but also by producing a small increase in the Kd. In brain membranes, Na+ (100 mM) and Ca2+ (2 mM) reduced the potency of bacitracin to inhibit [3H]nitrendipine binding by approximately sixfold with IC50 values of 2600 +/- 300 and 2100 +/- 400 micrograms/mL observed for bacitracin in the presence of 100 mM Na+ and 2 mM Ca2+, respectively. The EC50 values for the effects of Na+ and Ca2+ were 800 +/- 200 microM and 25 +/- 5 mM. K+, Mg2+, choline, and increasing the assay buffer of Tris-HCl to 50 mM also decreased the inhibition of [3H]nitrendipine binding by bacitracin. These results suggest that bacitracin specifically modulates [3H]nitrendipine binding in a cation-dependent manner and that brain and cardiac dihydropyridine binding sites are either biochemically different or exist in a different membrane environment.
Smith
J D
JD
Memorial University of Newfoundland, St. John's, Canada.
Bolger
G T
GT
D000818:Animals; D001414:Bacitracin / Q000494:pharmacology*; D001667:Binding, Competitive / Q000187:drug effects; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D015220:Calcium Channels; D002412:Cations / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D009568:Nitrendipine / Q000378:metabolism*; D051381:Rats; D011978:Receptors, Nicotinic / Q000378:metabolism
D015220:Calcium Channels; D002412:Cations; D011978:Receptors, Nicotinic; D001414:Bacitracin; D009568:Nitrendipine