Allosteric interaction of trimebutine maleate with dihydropyridine binding sites.
The effects of trimebutine maleate on [3H]nitrendipine binding to guinea-pig ileal smooth muscle membranes and Ca2(+)-induced contraction of the taenia cecum were studied. Specific binding of [3H]nitrendipine to smooth muscle membranes was saturable, with a KD value and maximum number of binding sites (Bmax) of 0.16 nM and 1070 fmol/mg protein, respectively. Trimebutine inhibited [3H]nitrendipine binding in a concentration-dependent manner with a Ki value of 9.3 microM. In the presence of trimebutine (10 microM), Scatchard analysis indicated a competitive-like inhibition with a decrease in the binding affinity (0.31 nM) without a change in Bmax (1059 fmol/mg protein). However, a dissociation experiment using trimebutine (10 or 100 microM) showed that the decreased affinity was due to an increase of the dissociation rate constant of [3H]nitrendipine binding to the membrane. In mechanical experiments using the taenia cecum, trimebutine (3-30 microM) caused a parallel rightward shift of the dose-response curve for the contractile response to a higher concentration range of Ca2+ under high-K+ conditions in a noncompetitive manner. These results suggest that trimebutine has negative allosteric interactions with 1,4-dihydropyridine binding sites on voltage-dependent Ca2+ channels and antagonizes Ca2+ influx, consequently inhibiting contractions of intestinal smooth muscle.
Nagasaki
M
M
Biological Research Laboratory, Tanabe Seiyaku Co., Ltd., Saitama, Japan.
Kurosawa
H
H
Naito
K
K
Tamaki
H
H
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D002432:Cecum / Q000378:metabolism / Q000648:ultrastructure; D004095:Dihydropyridines / Q000378:metabolism*; D006168:Guinea Pigs; D007082:Ileum / Q000378:metabolism / Q000648:ultrastructure; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000378:metabolism / Q000648:ultrastructure; D009568:Nitrendipine / Q000378:metabolism / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D014287:Trimebutine / Q000494:pharmacology*; D014316:Tritium
D015220:Calcium Channels; D004095:Dihydropyridines; D014316:Tritium; D009568:Nitrendipine; D014287:Trimebutine; D011188:Potassium; D002118:Calcium