Thermodynamic and kinetic aspects of agonist and antagonist binding to 1,4-dihydropyridine receptors.
The kinetic and equilibrium binding properties of the 1,4-dihydropyridine activator [3H](-)-S-Bay K 8644 and the antagonist [3H](+)-PN 200-110 were determined in rat heart membrane particulate preparations at temperatures between 4 and 37 degrees C. The binding of [3H](-)-S-Bay K 8644 was temperature-dependent with a single binding site with KD = 3.57 nM and Bmax = 330 fmol/mg.protein at 25 degrees C. The association and dissociation rate constants were 3.4 x 10(7) min-1 M-1 and 0.095 min-1 respectively at 25 degrees C and decreased slightly at lower temperatures. In contrast, [3H](+)-PN 200-110 bound to high (KD(H) = 0.032 nM, Bmax(H) = 316 fmol/mg.protein) and low affinity sites (KD(L) = 27.6 nM and Bmax(L) = 6432 fmol/mg.protein) at 25 degrees C in rat heart preparation. A similar two-site binding of [3H](+)-PN 200-110 was found in rat brain preparation, but only a single binding site was detected in rat skeletal muscle. Binding of [3H](+)-PN 200-110 to the high and low affinity sites in cardiac membranes was sensitive and insensitive respectively to temperature. Association and dissociation rates of [3H](+)-PN 200-110 at the high affinity binding sites were best fitted as mono-exponential functions. Association and dissociation rates of [3H](+)-PN 200-110 were 3.94 x 10(8) min-1 M-1 and 7.86 x 10(-3) min-1 at 25 degrees C. The association rate varied only slightly (3-fold), but the rate of dissociation decreased significantly (200-fold) with temperature from 37 to 4 degrees C. Thermodynamic analysis of equilibrium binding showed that the binding of activator was enthalpy driven, whereas the binding of antagonist to the high affinity site was both entropy- and enthalpy-driven and to the low affinity site was totally entropy-driven.
Zheng
W
W
Department of Biochemical Pharmacology, School of Pharmacy, State University of New York, Buffalo 14260.
Hawthorn
M
M
Triggle
D J
DJ
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000378:metabolism*; D015220:Calcium Channels; D004095:Dihydropyridines / Q000378:metabolism*; D017275:Isradipine; D007700:Kinetics; D008297:Male; D008566:Membranes / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism / Q000648:ultrastructure; D018733:Nicotinic Antagonists; D051381:Rats; D011919:Rats, Inbred Strains; D011978:Receptors, Nicotinic / Q000378:metabolism* / Q000502:physiology; D013816:Thermodynamics; D014316:Tritium
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004095:Dihydropyridines; D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic; D014316:Tritium; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D017275:Isradipine