Characterization of depolarization induced by palytoxin and grayanotoxin-I in isolated cardiac tissues from dogs and guinea pigs.
The mode of depolarizing action of palytoxin (PTX) was compared with that of grayanotoxin-I (GTX-I) to examine the site of action of PTX in cardiac tissues isolated from dogs and guinea pigs: PTX at above 1 X 10(-10) mol/l depolarized the membrane of canine Purkinje fibres, canine and guinea-pig ventricular muscles regardless of stimulation. The PTX-induced depolarization was resistant to 1 X 10(-5) mol/l tetrodotoxin (TTX) but was attenuated by low Na medium. GTX-I at 1 X 10(-5) mol/l depolarized the membrane of ventricular muscles from dogs and guinea pigs only when they were stimulated. Although GTX-I caused depolarization in Purkinje fibres in both stimulated and rested conditions, the effect was greater in stimulated fibres. In the presence of GTX-I, ventricular muscles generated long-lasting action potentials as a response to stimuli. TTX antagonized the GTX-I-action. After treatment of PTX, GTX-I still induced the long-lasting action potential and TTX could antagonize it. Ouabain at 1 X 10(-6) or 3 X 10(-6) mol/l partially inhibited the PTX-induced depolarization in guinea-pig papillary muscles. The data suggest that the TTX-sensitive Na channel is intact after treatment with PTX and that PTX acts on a site different from the Na channel, possibly on the Na+, K+-ATPase in cardiac cells.
Ito
K
K
Saruwatari
N
N
Mitani
K
K
Enomoto
Y
Y
D000178:Acrylamides; D000818:Animals; D003064:Cnidarian Venoms / Q000494:pharmacology*; D004224:Diterpenes / Q000494:pharmacology*; D004285:Dogs; D005260:Female; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009467:Neuromuscular Depolarizing Agents; D010042:Ouabain / Q000494:pharmacology; D010210:Papillary Muscles / Q000187:drug effects; D011690:Purkinje Fibers / Q000187:drug effects; D012964:Sodium / Q000502:physiology; D013045:Species Specificity; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D000095702:Polyether Toxins
D000178:Acrylamides; D003064:Cnidarian Venoms; D004224:Diterpenes; D009467:Neuromuscular Depolarizing Agents; D010042:Ouabain; D012964:Sodium; D013779:Tetrodotoxin; C010272:palytoxin; D000095702:Polyether Toxins; C001311:grayanotoxin I