FS2. a mamba venom toxin, is a specific blocker of the L-type calcium channels.
The peptide FS2 is a mamba venom toxin, consisting of 60 amino acids, three residues of which are different from those of calciseptine (CaS), a natural L-type Ca2+ channel blocker. The biological activities of synthetic FS2 for L-type Ca2+ channels were determined under comparisons to those of CaS and nitrendipine, a 1,4-dihydropyridine derivative. Similar to CaS, FS2 competitively inhibited the binding of [3H]nitrendipine to rat brain synaptosomal membranes on Lineweaver-Bulk plot, with Kd value of 210 nM, which was similar to that of CaS being 290 nM, but did not affect binding of an N-type Ca2+ channel ligand omega-[125I]-conotoxin GVIA to the membranes. Pretreatment of A7r5 cells with either FS2 or CaS at concentrations of 10(-8) M and greater for 5 min significantly and dose-dependently reduced 10(-6) M Bay K8644-induced increase in the cytosolic free Ca2+ concentration ([Ca2+]i) of the cells determined by the fluorescent Ca2+ indicator fura-2, with the half inhibitory concentrations (IC50) of 2.3 x 10(-8) and 2.7 x 10(-8) M, being similar to that of the IC50 value of nitrendipine (4.4 x 10(-8) M). These observations indicate that FS2, similar to CaS, is an active natural L-type Ca2+ blocker sharing the binding site on the channels with the 1,4-dihydropyridines.
Yasuda
O
O
Department of Geriatric Medicine, Osaka University Medical School, Japan.
Morimoto
S
S
Jiang
B
B
Kuroda
H
H
Kimura
T
T
Sakakibara
S
S
Fukuo
K
K
Chen
S
S
Tamatani
M
M
Ogihara
T
T
D000595:Amino Acid Sequence; D000818:Animals; D002121:Calcium Channel Blockers / Q000302:isolation & purification / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002478:Cells, Cultured; D004546:Elapid Venoms / Q000378:metabolism*; D017815:Elapidae; D008969:Molecular Sequence Data; D011869:Radioligand Assay; D051381:Rats; D014118:Toxins, Biological / Q000302:isolation & purification / Q000378:metabolism*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004546:Elapid Venoms; D014118:Toxins, Biological