SMOOTH-MUSCLE RELAXING AND HYPOTENSIVE ACTIVITIES OF SYNTHETIC CALCISEPTINE AND THE HOMOLOGOUS SNAKE-VENOM PEPTIDE FS2

The biological activities of synthetic calciseptine and FS2, a homolog ous peptide from snake venom, were determined using in vitro and in vi vo preparations. Calciseptine and FS2 produced dose-dependent relaxati on in pre-constricted rat aorta, pulmonary artery and trachea. The ons et and duration pattern of these relaxing effects were similar to thos e caused by nifedipine, an L-type Ca2+ channel blocker. Calciseptine r elaxed the contraction of rat aorta provoked by an L-type channel agon ist, Bay K 8644. This relaxation was not affected by N-G-nitro-L-argin ine, indomethacin or propranolol. Calciseptine and FS2 inhibited the c ontraction caused by acetylcholine in guinea pig ileal longitudinal mu scle. In case of in vivo study using anesthetized rats, calciseptine, FS2 and nifedipine showed depressor effects. The hypotensive effects o f the two peptides were more potent and sustained than that of nifedip ine. These findings show that both synthetic calciseptine and FS2 have similar biological activities like nifedipine, an L-type Ca2+ channel blocker. In addition, these two peptides with large molecular weights may be unique and useful tools for studying the Ca2+ channel.