Effect of neuraminidase on diltiazem-mediated alteration of nitrendipine binding in the hog coronary artery

A new Ca-antagonist, CD-349, binding to the Ca-channel of rat myocardium and brain and hog coronary artery

The binding to a Ca-channel of a novel 1,4-dihydropyridine (DHP) Ca-antagonist, 2-nitratopropyl 3-nitratopropyl 2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate (CD-349), was studied in rat myocardium and brain and hog coronary artery, and the binding was compared with that of other DHPs. In rat myocardium, the binding reaction of [3H]CD-349 was faster than that of nitrendipine (NTD). The association rate constant of [3H]CD-349 was about 10 times higher than that of [3H]NTD. The dissociation rate was also higher than that of [3H]NTD. Scatchard plot analysis of [3H]CD-349 binding showed one high affinity site for CD-349. The dissociation constant (Kd) and maximum number of binding sites (Bmax) were 333 pM and 286 fmoles/mg protein. They were almost the same as those for [3H]NTD. [3H]CD-349 and [3H]NTD bindings were dose dependently inhibited by 1,4-DHPs: nifedipine, nimodipine, nicardipine and CD-349. The order of the inhibitory potency of these drugs was CD-349 greater than nicardipine greater than nimodipine greater than nifedipine, when [3H]CD-349 and [3H]NTD were used as the ligands. Similar results were obtained for rat brain and hog coronary artery. [3H]CD-349 binding was not changed by alpha- or beta-adrenergic, cholinergic, histaminergic or serotonergic agents in rat myocardium. From these results, it is suggested that CD-349 binds to the Ca-channel reversibly with high affinity due to its high association rate for the site.

Characterization of calcium channel antagonist binding sites labeled by [3H]nitrendipine in porcine coronary artery and aorta

The receptor sites for dihydropyridine calcium channel antagonists in porcine coronary artery were characterized with [3H]nitrendipine (NTD), and were compared with those in the thoracic aorta. Specific [3H]NTD binding in the coronary artery and aorta was saturable, reversible and of high affinity. These sites showed a pharmacological specificity and stereoselectivity characteristic of the receptor sites for dihydropyridine calcium channel antagonists. The pharmacological potencies of nitrendipine, nifedipine, nisoldipine, (+)-PN 200-110 and (-)-PN 200-110 in the isolated porcine coronary artery correlated well with their potencies in competing for [3H]NTD binding sites. The Hill coefficients for the competition curves for these antagonists in the porcine coronary artery and aorta were close to one. Verapamil partially inhibited specific [3H]NTD binding in both tissues. The [3H]NTD binding was increased by Mg2+ and Ca2+ but was markedly reduced by EDTA. Thus, the present study has shown that [3H]NTD selectively labels the pharmacologically relevant dihydropyridine receptors in the porcine coronary artery and that there is no significant difference between the binding characteristics of the receptor sites in the coronary artery and aorta of pigs.