Age-related changes in calcium antagonist receptors in rabbit ureter

(+)-[3H]PN 200-110 (a dihydropyridine calcium channel antagonist) binding sites were studied in ureters of 1-day (neonatal), 6-week (premature), 6-month (young) and 4.5- to 5-year (old) female rabbits. Specific binding of (+)-[3H]PN 200-110 to ureteral membrane particulates was saturable, reversible and of high affinity. The densities (Bmax) of (+)-[3H]PN 200-110 binding sites were 46.7 +/- 2.5, 22.6 +/- 2.0, 12.7 +/- 1.8 and 11.9 +/- 1.6 fmol/mg protein in 1-day, 6-week, 6-month and 4.5- to 5-year rabbit ureters, respectively. The affinity constants (KD) of the binding sites for (+)-[3H]PN 200-110 were similar in all groups. Calcium agonists and antagonists inhibited (+)-[3H]PN 200-110 binding to 1-day and 6-week rabbit ureters with the following rank order of Ki values: nitrendipine < nifedipine < BAY K 8644 < verapamil. There were no significant differences in Ki values between the neonatal and premature groups. The data demonstrate the presence of an age-related down-regulation of (+)-[3H]PN 200-110 binding sites in rabbit ureteral membrane particulates.