Palytoxin-induced contraction and release of endogenous noradrenaline in rat tail artery.
1. The mechanism of the contractile effect of a potent marine toxin, palytoxin (PTX) on the rat isolated tail artery was examined. 2. PTX (10(-7) M) induced a contraction in the tail artery which was dependent on external Ca2+. This contraction was inhibited (by 75% or more) by 10(-6) M prazosin, 2.4 x 10(-5) M bretylium and 10(-4) M 6-hydroxydopamine (6-OHDA), and partially (by 40%) by 10(-5) M indomethacin. However, this contraction was not affected by 10(-6) M tetrodotoxin (TTX), 10(-6) M nifedipine or reserpine treatment. The PTX-induced contraction in reserpine-treated artery was partially inhibited by nifedipine and indomethacin but not by prazosin. 3. Transmural electrical stimulation induced a transient contraction which was dependent on external Ca2+. The contraction induced by electrical stimulation was inhibited by TTX, prazosin, bretylium, reserpine treatment and 6-OHDA but not by nifedipine or indomethacin. 4. PTX increased the release of noradrenaline from this artery. However PTX did not release noradrenaline from reserpine-treated arteries. PTX-induced noradrenaline release was only partially inhibited by TTX or by Ca2+-free solution. 5. These results suggest that PTX has pre- and postsynaptic effects in the rat tail artery. PTX may stimulate adrenergic nerves and release noradrenaline mainly by a TTX-insensitive and Ca2+-independent mechanism and partially by a TTX-sensitive and Ca2+-dependent mechanism. Further, PTX may also release prostaglandins and depolarize smooth muscle cell membrane to induce a contraction.
Karaki
H
H
Department of Veterinary Pharmacology, Faculty of Agriculture, University of Tokyo, Bunkyo-ku.
Nagase
H
H
Ohizumi
Y
Y
Satake
N
N
Shibata
S
S
D000178:Acrylamides; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000502:physiology; D003064:Cnidarian Venoms / Q000494:pharmacology*; D004558:Electric Stimulation; D006892:Hydroxydopamines / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism*; D016627:Oxidopamine; D051381:Rats; D011919:Rats, Inbred Strains; D012110:Reserpine / Q000494:pharmacology; D000095702:Polyether Toxins
D000178:Acrylamides; D002118:Calcium; D003064:Cnidarian Venoms; D006892:Hydroxydopamines; D009543:Nifedipine; D009638:Norepinephrine; D016627:Oxidopamine; D012110:Reserpine; C010272:palytoxin; D000095702:Polyether Toxins