Divalent cations increase the binding capacity of the [3H]mepyramine binding site, a possible histamine H1 receptor, in rat liver membranes.
The [3H]mepyramine binding to rat liver membranes was about 2-fold higher in the presence of 2 mM CaCl2 than in the absence. However, the [3H]mepyramine binding to rat brain membranes was not affected by the presence of 2 mM CaCl2. Scatchard analysis showed that 2 mM CaCl2 did not change the affinity (KD) of liver membranes to [3H]mepyramine, but increased the binding capacity (Bmax). CaCl2 had a half maximal effect (ED50) at 3 microM and a maximal effect at concentrations of more than 10 microM. Other divalent cations, Mg++, Mn++, Sr++ and Ba++, also increased the [3H]mepyramine binding, whereas monovalent cations, Na+, K+, Li+ and Rb+, had no effect.
Fukui
H
H
Department of Pharmacology II, Osaka University School of Medicine, Japan.
Wang
N P
NP
Sawai
S
S
Tanaka
F
F
Wada
H
H
D000631:Aminopyridines / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D002412:Cations / Q000494:pharmacology*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011738:Pyrilamine / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011969:Receptors, Histamine H1 / Q000187:drug effects / Q000378:metabolism*
D000631:Aminopyridines; D002412:Cations; D011506:Proteins; D011969:Receptors, Histamine H1; D011738:Pyrilamine; D002118:Calcium