title: Inhibition by amiloride and quinacrine of specific [3H]nitrendipine binding to rat cardiac membranes.
abstract: Binding studies were designed to test if and how amiloride and quinacrine affected the specific binding of [3H]nitrendipine (NIT) to rat cardiac membranes. Specific binding of NIT was inhibited in a dose-dependent manner by amiloride [Hill coefficient (nH), 1.46; concentration of inhibitor producing 50% inhibition (K0.5) = 9.2 x 10(-4) M] and quinacrine (nH = 0.54, K0.5 = 7.7 x 10(-6) M). The inhibitions were incomplete in the presence of 10(-3) M Ca ions. The Hofstee plot was convex upwards for amiloride and concave upwards for quinacrine. Amiloride increased the Kd, decreased the maximum specific binding and increased the k-1. Quinacrine increased the Kd without changing the maximum specific binding and increased the k-1. The effects of amiloride and quinacrine on k-1 were nonadditive. We conclude that amiloride and quinacrine bind to or close to the L-type Ca channel, and inhibit the specific binding of NIT by allosteric, complex interactions influenced by the free concentration of Ca++. The nonadditive allosteric effects suggest a shared mechanism of interaction for amiloride and quinacrine with the site(s) of NIT. Several mechanisms are discussed to explain how amiloride and quinacrine can produce such inhibition of NIT binding.
authors.affiliation: Department of Pharmacology, University of Oslo, Blindern, Norway.
authors.forename: M
authors.initials: M
authors.lastname: Stokke
authors.forename: E M
authors.initials: EM
authors.lastname: Hagelin
authors.forename: C
authors.initials: C
authors.lastname: Poulsson
authors.forename: R
authors.initials: R
authors.lastname: Patel
authors.forename: Y
authors.initials: Y
authors.lastname: Haile
authors.forename: O
authors.initials: O
authors.lastname: Brørs
mesh_terms: D000494:Allosteric Regulation; D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009568:Nitrendipine / Q000378:metabolism*; D011796:Quinacrine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D000584:Amiloride; D009568:Nitrendipine; D011796:Quinacrine