Drugs online research references
Cell Mol Neurobiol. 1995 Aug;15(4):495-500.
Block by 5-hydroxytryptamine of neuronal acetylcholine receptor channels expressed in Xenopus oocytes.
Nakazawa K, Akiyama T, Inoue K.
Division of Pharmacology, National Institute of Health Sciences, Tokyo, Japan.
1. Effects of 5-hydroxytryptamine (5-HT) on neuronal nicotinic acetylcholine (ACh) receptor channels were investigated by expressing cloned channel subunits in Xenopus oocytes. 2. When channels were expressed with a combination of alpha 3 and beta 4 subunits, 5-HT (10 to 300 microM) reversibly inhibited an inward current activated by 100 microM ACh in a concentration-dependent manner. The inhibition was also observed when alpha 3 subunit was combined with beta 2 subunit instead of beta 4 subunit, or beta 4 subunit was combined with alpha 2 or alpha 4-1 subunit instead of alpha 3 subunit to express channels. 3. Compounds known to antagonize at 5-HT receptors (LY53857, metoclopramide and propranolol) exhibited an agonistic effect: they inhibited the ACh-activated current. 4. The results suggest that 5-HT inhibits recombinant neuronal nicotinic receptor channels through a binding-site distinct from conventional 5-HT receptors. The binding-site may not be attributed to a unique type of channel subunits.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8565050&dopt=Abstract
Nat Toxins. 1995;3(5):355-62.
Cooliatoxin, the first toxin from Coolia monotis (Dinophyceae).
Holmes MJ, Lewis RJ, Jones A, Hoy AW.
Southern Fisheries Centre, QDPI, University of Queensland, Australia.
Coolia monotis is a benthic dinoflagellate previously thought to be non-toxic. We describe a new toxin, named cooliatoxin, purified from cultures of a strain of C. monotis isolated from Australia. Cooliatoxin is likely a mono-sulphated, polyether toxin (M = 1,062; i.p. LD50 = 1 mg/kg in mice) that induces hypothermia and respiratory failure in mice after a pronounced delay period during which there are no obvious signs of intoxication. These signs in mice are similar to those reported for the shellfish toxin named yessotoxin and the molecular weight of cooliatoxin corresponds to the mono-sulphated form of yessotoxin, suggesting that cooliatoxin may be an analogue of yessotoxin. Cooliatoxin has no effect on the mouse phrenic nerve or diaphragm musculature in vitro but causes initial stimulation and subsequent block of unmylenated nerves in vitro. In isolated guinea pig left atria, cooliatoxin (above 20 nm) induced a slow developing concentration dependent sustained inotropic response. Propranolol or tetrodotoxin reversed the positive inotropic effects, indicating that the majority of the cooliatoxin induced response was mediated by stimulation of nerves associated with the atrial musculature, resulting in the release of noradrenaline. Cooliatoxin induced transient contractions in isolated guinea pig vas deferens preparations. Atria and vas deferens preparations were tachyphylactic to a second equivalent dose of cooliatoxin applied after the effects of the first dose had diminished. The observed in vitro effects of cooliatoxin on peripheral nerves are unlikely to account for the lethal effects in mice and a central action of this toxin is suspected.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8581320&dopt=Abstract
Gastroenterology. 1981 Jan;80(1):51-4.
Effect of dopamine on opossum duodenal smooth muscle.
Anuras S.
Opossum duodenum was cut into 2 mm X 1.5 cm strips. The strips cut along the oral-caudal axis were called longitudinal strips, while those cut 90 degrees to that axis were called circular strips. Dopamine produced contractions in both muscle layers. ED 50 for the longitudinal and circular muscle was 2.8 X 10(-6) M and 1.9 X 10(-5) M, respectively. The longitudinal muscle was 6.5 times more sensitive to dopamine than the circular muscle. The dopamine-produced contractions were completely blocked by phenoxybenzamine, 10(-4) M, and phentolamine, 10(-5) M. Haloperidol, 10(-5) M, or bulbocapnine, 10(-5), completely or partially blocked the contractions produced by dopamine in only one-third of the strips. Tetrodotoxin, propranolol, atropine, and curare did not affect the dopamine-produced contractions. These studies suggest that dopamine mainly stimulates alpha-excitatory adrenergic receptors in opossum duodenal muscle and that the longitudinal muscle is more sensitive to dopamine. However, we cannot exclude the existence of excitatory dopamine receptors in the opossum duodenal smooth muscle.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7450411&dopt=Abstract
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