neuropeptide-y and palytoxin

A combination of pharmacological, histochemical, immunocytochemical, neurochemical and microscopic techniques has been used to test the hypothesis that smooth muscle contractions caused by palytoxin are primarily a response to toxin-induced release of transmitter from motor nerve terminals. In the anococcygeus, palytoxin caused a dose-dependent contraction; the dose-response curve was particularly steep in the dose range 0.3-100 nM. This part of the response was abolished by phentolamine and absent in the muscles of reserpinized animals. A single, large dose of palytoxin (100 nM) caused a biphasic contraction. Phentolamine blocked the first phase by 50% and the second by > 80%. Transmitter overflow studies showed that the toxin enhanced the release of 3H after loading with 3H-NA, and immunofluorescence showed the loss of adrenergic transmitters from the innervation. In the vas deferens, palytoxin caused a biphasic contraction of the muscle. Phentolamine blocked first phase by > 80% and the second by 47%. Immunofluorescence studies showed that stores of adrenergic transmitter were depleted but stores of NPY were not greatly affected. Indirect evidence suggested that palytoxin did not cause the release of purinergic transmitters. A direct component to the contraction was apparently present in most preparations, but though variable in extent it was usually slight. It is concluded that the contractions of smooth muscle caused by palytoxin are primarily the result of toxin-induced transmitter release.

Topics: Acrylamides; Animals; Autonomic Nervous System; Cnidarian Venoms; Dose-Response Relationship, Drug; Drug Interactions; Drug Synergism; Immunohistochemistry; In Vitro Techniques; Male; Microscopy, Fluorescence; Motor Neurons; Muscle Contraction; Muscle, Smooth; Nerve Endings; Neuropeptide Y; Neurotransmitter Agents; Nifedipine; Norepinephrine; Phentolamine; Rats; Rats, Wistar; Tetrodotoxin; Vas Deferens

1. The effects of a coelenterate toxin, palytoxin (PTX) have been studied in the isolated detrusor muscle. of the rat. 2. PTX (1-100 nM) initiated concentration-dependent contractions of the detrusor; the contraction led to an irreversible tachyphylaxis. Muscle desensitized to PTX continued to respond to acetylcholine (ACh) and excess K+ but the contractions were reduced compared to pre-PTX contractions. 3. Contractions evoked by PTX were not affected by the presence of atropine (10 microM), indomethacin (10 microM) or tetrodotoxin (0.5 microM) but were greatly reduced by nifedipine (3 microM) and by the absence of K+. PTX could not evoke contractions in the absence of Ca2+ or in tissues depolarized by exposure to excess K+. 4. PTX abolished the neurogenic contractile responses to electrical field stimulation (EFS). 5. Combined treatment with atropine (10 microM) plus nifedipine (3 microM) abolished contractile responses to EFS and greatly reduced the contractile response to PTX. 6. The contractile response to PTX (100 nM) was reduced following exposure of the muscle to alpha, beta-methylene ATP. 7. Exposure to PTX (100 nM) for 1-3 h reduced both the ACh content of the detrusor (by more than 80%), and the immunoreactivity of neuropeptide Y-containing nerve fibres compared to control. 8. It is concluded that the primary effect of PTX is to promote the release of endogenous motor transmitters, leading to their eventual depletion.

Topics: Acetylcholine; Acrylamides; Animals; Calcium; Cnidarian Venoms; Electric Stimulation; Immunohistochemistry; In Vitro Techniques; Male; Muscle Contraction; Muscle Tonus; Muscle, Smooth; Neuropeptide Y; Potassium; Rats; Rats, Wistar; Receptors, Purinergic; Synaptic Transmission