title: BAY K 8644, a 1,4-dihydropyridine Ca2+ channel activator: dissociation of binding and functional effects in brain synaptosomes.
abstract: K+-stimulated 45Ca2+ uptake into rat brain and guinea pig cerebral cortex synaptosomes was measured at 10 s and 90 s at K+ concentrations of 5-75 mM. Net increases in 45Ca2+ uptake were observed in rat and guinea pig brain synaptosomes. 45Ca2+ uptake under resting or depolarizing conditions was not increased by the 1,4-dihydropyridine BAY K 8644, which has been shown to activate Ca2+ channels in smooth and cardiac muscle. High-affinity [3H]nitrendipine binding in guinea pig synaptosomes (KD = 1.2 X 10(-10) M, Bmax = 0.56 pmol mg-1 protein) was competitively displaced with high affinity (IC50 2.3 X 10(-9) M) by BAY K 8644. Thus high-affinity Ca2+ channel antagonist and activator binding sites exist in synaptosome preparations, but their relationship to functional Ca2+ channels is not clear.
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers; D002540:Cerebral Cortex / Q000378:metabolism; D006168:Guinea Pigs; D007473:Ion Channels / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D009543:Nifedipine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D009568:Nitrendipine; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D013574:Synaptosomes / Q000378:metabolism*
chemical_list: D002121:Calcium Channel Blockers; D007473:Ion Channels; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009568:Nitrendipine; D009543:Nifedipine; D011188:Potassium; D002118:Calcium