Effects of trachynilysin, a protein isolated from stonefish (Synanceia trachynis) venom, on frog atrial heart muscle.
The effects of trachynilysin (TLY), a protein toxin isolated from stonefish (Synanceia trachynis) venom, were studied on the electrical and mechanical activities of frog atrial fibres. TLY (1 microg/ml) hyperpolarized the membrane, shortened the action potential (AP) duration (APD), exerted a negative inotropic effect and elicited contracture. These effects did not develop in the presence of atropine. TLY shortened the APD of fibres isolated from a frog completely paralyzed with botulinum type A toxin, in the presence of Ca2+ but not when Ca2+ was replaced by Sr2+. TLY increased the basal and the peak of the fluorescence ratio of stimulated fibres loaded with fura-2. Confocal laser scanning microscopy revealed the existence of a diffuse innervation in atrial tissue. Our results suggest that TLY enhances the release of acetylcholine from atrial cholinergic nerve terminals and activates indirectly muscarinic receptors leading to a shortening of APD. They also show that the mechanical effects induced by TLY are due to an increase of the Ca2+ influx and to a rise in intracellular Ca2+ levels which leads to (i) a slowing of the Na+/Ca2+ exchange activity, which accounts for the contracture and (ii) the activation of a Ca2+-dependent K+ current involved in the APD shortening.
Sauviat
M P
MP
Unité INSERM 451, Laboratoire d'Optique Appliquée, Ecole Polytechnique-ENSTA, Centre de l'Yvette, Palaiseau, France. sauviat@enstay.ensta.fr
Meunier
F A
FA
Kreger
A
A
Molgó
J
J
D000109:Acetylcholine / Q000378:metabolism; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D004347:Drug Interactions; D004558:Electric Stimulation; D005397:Fish Venoms / Q000494:pharmacology*; D005399:Fishes; D006325:Heart Atria / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects*; D009498:Neurotoxins / Q000494:pharmacology*; D011893:Rana esculenta
D005397:Fish Venoms; D009498:Neurotoxins; C103845:trachynilysin; D001285:Atropine; D000109:Acetylcholine; D002118:Calcium