Calcium-binding of Synaptosomes isolated from rat brain cortex. II. Inhibitory effects of magnesium ions and some other cations.
As in our previous report (Kamino, Uyesaka & Inouye, J. Membrane Biol. 17:13 1974), the absorbance changes of murexide caused by Ca2+ and followed up by a dual wavelength spectrophotometer were applied to measure synaptosomal Ca2+-binding in the presence of cations such as Rb+, Mn2+ or La3+. All the cations tested showed a significant inhibition of synaptosomal Ca2+-binding except Li+. The inhibitory effects could be divided into the following three categories: (1) noncompetive, co-operative K+-type, which includes alkali metal ions. The potency of inhibition is K+ greater than Rb+ greater than Cs+ greater than Li+, Na+ =0; (2) competitive Mn2+ -type which includes many divalent cations. The inhibitory potency was found to be in the following order: Mn2+ greater than Sr2+ greater than Cd2+, Ba2+ greater than Mg2+; (3) nonspecific, noncompetitive La3+ -type; among the cations tested, La3+ and Ce3+ were found to markedly reduce the Ca-binding capacity of synaptosomal particles, resulting in a noncompetitive inhibition, at least in the range of Ca2+ concentration used.
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent; D002414:Cations, Monovalent; D002540:Cerebral Cortex / Q000378:metabolism*; D007700:Kinetics; D007811:Lanthanum / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology*; D008433:Mathematics; D051381:Rats; D011955:Receptors, Drug / Q000187:drug effects*; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*
D002413:Cations, Divalent; D002414:Cations, Monovalent; D011955:Receptors, Drug; D007811:Lanthanum; D008274:Magnesium; D002118:Calcium