Smooth Muscle Relaxing and Hypotensive Activities of Synthetic Calciseptine and the Homologous Snake Venom Peptide FS₂

Abstract

activities of synthetic calciseptine and FS₂, a homologous peptide from snake venom, were determined using in vitro and in vivo preparations. Calciseptine and FS₂ produced dosedependent relaxation in pre-constricted rat aorta, pulmonary artery and trachea. The onset and duration pattern of these relaxing effects were similar to those caused by nifedipine, an L-type Ca²⁺ channel blocker. Calciseptine relaxed the contraction of rat aorta provoked by an L-type channel agonist, Bay K 8644. This relaxation was not affected by N^G-nitro-L-arginine, indomethacin or propranolol. Calciseptine and FS₂ inhibited the contraction caused by acetylcholine in guinea pig ileal longitudinal muscle. In case of in vivo study using anesthetized rats, calciseptine, FS₂ and nifedipine showed depressor effects. The hypotensive effects of the two peptides were more potent and sustained than that of nifedipine. 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.