The effects of crude venoms of Conus magus and Conus striatus on the contractile response and electrical activity of guinea-pig cardiac musculature.

R. Endean, P. Gyr and J. Surridge. The effects of crude venoms of Conus magus and Conus striatus on the contractile response and electrical activity of guinea-pig cardiac musculature. Toxicon17, 381–395, 1979.—Positive inotropic activity of long duration elicited in atrial or ventricular musculature by the venom of Conus striatus or that of C. magus can be antagonized by manganese, lanthanum, verapamil or tetrodotoxin. The block of ventricular contractility by each of these four blocking agents can be overcome by either venom as can the block of atrial contractility by tetrodotoxin or lanthanum. Positive inotropic activity similar to that in non-reserpinized guinea-pigs was produced in ventricular musculature from reserpinized guinea-pigs by standard doses of either venom but atrial musculature from reserpinized guinea-pigs required increased amounts of the venoms before such activity was exhibited. Although the crude venoms did not affect resting potentials they caused marked increases in overshoot and overall duration of action potentials in both atrial and ventricular musculature. The abolishing, by manganese and lanthanum, of the plateau of the action potentials in atrial musculature was reversed by C. striatus venom but not C. magus. The venom of C. magus, but not C. striatus, antagonizes the depressant effect of tetrodotoxin on the rate of rise and overshoot of the action potential of atrial or ventricular musculature.