Calciseptine binding to a 1,4-dihydropyridine recognition site of the L-type calcium channel of rat synaptosomal membranes.
Calciseptine (CaS) is a natural peptidic L-type Ca2+ channel blocker consisting of 60 amino acids with four disulfide bonds. The effects of synthetic CaS on the binding of various ligands to Ca2+ channels of rat brain synaptosomal membranes were studied. The membranes possessed specific binding sites for L-type Ca2+ channel ligands [3H]nitrendipine, [3H]diltiazem and [3H]verapamil, derivatives of 1,4-dihydropyridine, benzothiazepine and papaverine, respectively, and also for N-type Ca2+ channel ligand omega-[125I]-conotoxin GVIA (omega-[125I]CTX). Lineweaver-Bulk plot analysis disclosed that CaS competitively inhibited the binding of [3H]nitrendipine, with maximal binding capacity of 0.19 pmol/mg protein and dissociation constant (Kd) of 290 nM, being about 10(3) times the Kd value of [3H]nitrendipine. Similar to nitrendipine, CaS noncompetitively enhanced the binding of [3H]diltiazem, but did not affect the binding of [3']verapamil. CaS at up to 10.0 microM did not affect the binding of omega-[125I]CTX. These observations indicate that CaS shares the properties of 1,4-dihydropyridine derivatives, and allosterically modulates the binding of other L-type Ca2+ channel ligands.
Department of Geriatric Medicine, Osaka University Medical School, Japan.
O
O
Yasuda
S
S
Morimoto
Y
Y
Chen
B
B
Jiang
T
T
Kimura
S
S
Sakakibara
E
E
Koh
K
K
Fukuo
S
S
Kitano
T
T
Ogihara
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002458:Cell Fractionation; D004095:Dihydropyridines / Q000378:metabolism*; D004110:Diltiazem / Q000378:metabolism; D004546:Elapid Venoms / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D008297:Male; D009568:Nitrendipine / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013574:Synaptosomes / Q000378:metabolism* / Q000648:ultrastructure; D014700:Verapamil / Q000378:metabolism; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004095:Dihydropyridines; D004546:Elapid Venoms; D008024:Ligands; D010455:Peptides; D020960:omega-Conotoxins; C053423:Conus magus toxin; C067971:calciseptine; D009568:Nitrendipine; D014700:Verapamil; D004110:Diltiazem