title: Purification, subunit structure and pharmacological effects on cardiac and smooth muscle cells of a polypeptide toxin isolated from the marine snail Conus tessulatus.
abstract: The most active component in smooth muscle contraction, isolated from the whole venom of the marine snail Conus tessulatus, has a molecular mass of about 55 kDa. The toxin protein, tessulatus toxin, appeared to be constituted by two distinct polypeptide bands of 26 kDa and 29 kDa. The pure toxin caused a marked contraction of both guinea-pig ileum and rabbit aorta at nanomolar concentrations. Tessulatus-toxin-induced contraction was indirectly prevented by classical inhibitors of the voltage-dependent Ca2+ channel. Tessulatus toxin caused a large increase in the initial rate of 45Ca2+ uptake by cardiac cells. This uptake was insensitive to Ca2+ channel blockers at concentrations 100-1000 fold higher than those known to block voltage-dependent Ca2+ channels in these cells. Voltage clamp experiments have confirmed that tessulatus toxin was not directly active on the Ca2+ current. Tessulatus-toxin-stimulated 45Ca2+ influx was inhibited by dichlorobenzamil and suppressed when Na+ was substituted by Li+, indicating that the toxin acted via activation of the Na+/Ca2+ exchange system in cardiac cells. Activation by tessulatus toxin of the Na+/Ca2+ exchange system occurred via a toxin-stimulated Na+ entry into cardiac cells and was observed in the same range of toxin concentration which produced 45Ca2+ entry. The Na+ entry system that was activated by tessulatus toxin was insensitive to classic inhibitors of known Na+ entry systems in cardiac cells. Possible mechanisms by which tessulatus toxin induced Na+ entry into cardiac cells and contractions in smooth muscles are discussed. Tessulatus toxin is cytotoxic when used at high concentrations.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D004591:Electrophoresis, Polyacrylamide Gel; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D008978:Mollusk Venoms / Q000302:isolation & purification*; D009130:Muscle, Smooth / Q000187:drug effects*; D009206:Myocardium / Q000378:metabolism; D011817:Rabbits; D012908:Snails / Q000032:analysis*; D012964:Sodium / Q000378:metabolism
chemical_list: D007473:Ion Channels; D008978:Mollusk Venoms; C037829:tessulatoxin; D012964:Sodium; D002118:Calcium