title: Effects of palytoxin on contractile response and calcium movement in guinea-pig taenia coli.
abstract: PTX (10(-8)M) induced a rapid increase followed by a gradual decrease in muscle tension in normal physiological salt solution (PSS), while it induced a slow increase in muscle tension in low-Na+ solution. These contractions were inhibited by Ca2+ channel blockers, verapamil and nicardipine. PTX rapidly increased tissue Na+ and decreased tissue K+ contents in normal PSS. In low-Na+ solution, PTX decreased tissue K+ content with a slower rate than that in normal PSS. PTX increased uptake of 45Ca2+ in normal as well as low-Na+ solutions with similar time course as the increase in muscle tension. However, 45Ca2+ uptake still remained high when the PTX-induced transient contraction ceased. These results suggest that PTX increases Ca2+ influx through voltage-dependent Ca2+ channels to cause contraction. After a prolonged exposure to PTX, however, muscle tension is uncoupled from Ca2+ influx.
mesh_terms: D000178:Acrylamides; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003064:Cnidarian Venoms / Q000494:pharmacology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D012503:Saponins / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology; D000095702:Polyether Toxins
chemical_list: D000178:Acrylamides; D000255:Adenosine Triphosphate; D002118:Calcium; D003064:Cnidarian Venoms; D007473:Ion Channels; D010042:Ouabain; D011188:Potassium; D012503:Saponins; D012964:Sodium; D014700:Verapamil; C010272:palytoxin; D000095702:Polyether Toxins