Influence of Bistramide A on the twitch tension in rat atrial heart muscle.
Bistramide A, a new toxin isolated from the Urochordate Lissoclinum bistratum Sluiter, was applied to rat auricular heart muscle bundles. At a stimulation frequency of 0.2 Hz, the toxin induces a dose-dependent reduction of the stimulated twitch tension force; it decreases Vmax and shortens the duration of the plateau and the slow repolarizing phase of the action potential. In the control solution, switching from a stimulation frequency of 0.2 Hz to 1 Hz decreases the force with which a positive potentiation develops either at a maintained high frequency or after switching from 1 Hz to 0.2 Hz. Bistramide A reduces both the force evoked at 1 Hz and the potentiation. The data suggest that Bistramide A blocks Na+ conductance; inhibits Ca++ channels in a time- and frequency-dependent manner; reduces Na(+)-Ca++ exchange activity; but does not modify the ability of the sarcoplasmic reticulum to be refilled although the rate of Ca++ accumulation is decreased.
Sauviat
M P
MP
Laboratoire de Physiologie Cellulaire, ERS CNRS F0100, Université de Paris XI, Orsay, France.
Chesnais
J M
JM
Diacono
J
J
Biard
J F
JF
Verbist
J F
JF
D000081:Acetamides; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D016275:Atrial Function; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology; D003864:Depression, Chemical; D004553:Electric Conductivity; D004988:Ethers, Cyclic / Q000494:pharmacology*; D006325:Heart Atria / Q000187:drug effects; D007700:Kinetics; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D011714:Pyrans; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D013141:Spiro Compounds
D000081:Acetamides; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004988:Ethers, Cyclic; D011714:Pyrans; D013141:Spiro Compounds; C059975:bistratene A; D012964:Sodium; D002118:Calcium