title: Developmental changes of cerebral cortical [3H]clonidine binding in rats: influences of guanine nucleotide and cations.
abstract: Cerebral cortical [3H]clonidine binding and influences of GTP and cations were investigated in developing rats. The results from Scatchard plots were compatible with the presence of two populations of binding sites [high-affinity binding (KD = 0.59 nM) and low-affinity binding (KD = 7.12 nM)] in 70-day-old rats but only high-affinity binding (KD = 0.27 nM) on day 1. Low-affinity binding was detectable on day 7. KD values in high- and low-affinity binding were not significantly changed during development after 7 days. Bmax of high-affinity binding reached a peak on day 15, and the value of low-affinity binding gradually increased with age. The addition of 10 microM GTP caused a significant reduction in Bmax of high-affinity binding after day 7. Neither KD nor Bmax of low-affinity binding was affected by 10 microM GTP during development. NaCl (10 and 100 mM) diminished the binding on days 7 and 70. MnCl2 (0.1 and 1.0 mM) markedly increased the binding on days 15 and 70 but not on day 7. It is suggested that: (1) single binding sites of alpha 2-adrenoceptors with higher affinity seem to be present on day 1; (2) low-affinity binding appears on day 7; (3) the number of high-affinity binding sites reaches a peak on day 15, followed by changes in populations of high-affinity as well as low-affinity sites without changing affinity; (4) the regulatory mechanism in alpha 2-receptors by guanine nucleotide reaches functional maturity between days 1 and 7; and (5) the involvement of Na+ and Mn2+ in alpha 2-receptor binding becomes functional by days 7 and 15, respectively.
mesh_terms: D000375:Aging; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D003000:Clonidine / Q000378:metabolism*; D005260:Female; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D054755:Imidazoline Receptors; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2
chemical_list: D054755:Imidazoline Receptors; D011942:Receptors, Adrenergic, alpha; D018341:Receptors, Adrenergic, alpha-2; D006160:Guanosine Triphosphate; D003000:Clonidine