Ouabain caused

Cells are normally kept at osmotic (water activity) equilibrium by the action of the Na-pump. Inhibition of the pump with the specific Na -K -ATPase inhibitor, ouabain, causes cell swelling as does inhibition of it by hypothermia. The intracellular environment contains a high concentration of K (100 to 120 mM, in most mammalian cells), lower concentrations of Na (about 10 to 30 mM), and high... 

Tissue Culture Assay. Kogure et al. (48) report a novel tissue culture assay for detecting several types of sodium channel blockers. The mouse neuroblastoma cell line ATCC CCL 131 is grown in RPMI 1640 supplemented with 13.5% fetal bovine serum and 100 pg/ml gentamycin, in an atmosphere of 5% C0 95% air at 37 C. Ninety-six well plates are seeded with 1 x 10 cells in 200 pi of medium containing 1 mM ouabain and 0.075 mM veratridine. Veratridine and ouabain cause neuroblastoma cells to round-up and die. In the presence of sodium channel blockers (e.g., TTXs or STXs), the lethal action of veratridine is obviated and cells retain normal morphology and viability. An important feature of this assay is that a positive test for sodium channel blockers results in normal cell viability. Since bacterial extracts can contain cytotoxic components, this assay offers an advantage over tests that use cell death as an endpoint. The minimum detectable level of TTX is approximately 3 nM, or approximately 1/1000 mouse unit. 

Palytoxin (PTX), isolated from the zanthid Palythoa species, caused a rapid contraction followed by a slow phasic contraction of the guinea pig vas deferens. The second component of PTX-induced contraction was markedly inhibited by adrenergic blocking agents, whereas the first component was blocked by ouabain. In pheochromocytoma cells,... 

Palytoxin (PTX) is one of the most potent marine toxins known and the lethal dose (LD q) of the toxin in mice is 0.5 Mg/kg when injected i.v. The molecular structure of the toxin has been determined fully (1,2). PTX causes contractions in smooth muscle (i) and has a positive inotropic action in cardiac muscle (4-6). PTX also induces membrane depolarization in intestinal smooth (i), skeletal (4), and heart muscles (5-7), myelinated fibers (8), spinal cord (9), and squid axons (10). PTX has been demonstrated to cause NE release from adrenergic neurons (11,12). Biochemical studies have indicated that PTX causes a release of K from erythrocytes, which is followed by hemolysis (13-15). The PTX-induced release of K from erythrocytes is depress by ouabain and that the binding of ouabain to the membrane fragments is inhibited by PTX (15). 

Mechanical Response. PTX (5 x 10" to 3 x 10 M) caused a concentration-dependent contraction of the guinea pig vas deferens. The configuration of contractile response indicated the presence of two components, an initial rapid component followed by a second slow component. The first component of the response to PTX was abolished after treatment with Mg (10 mM), Ca -free medium, or ouabain (10 M), but remained almost unaffected by phentolamine (10 M), reserpine, 6-OHDA, atropine, or mecamylamine (10" M). The second component of the response to PTX was also completely inhibited after the incubation in the high or Ca -free medium. Phentolamine, reserpine, or 6-... 

In addition to genotoxicify studies with chlorophenols themselves, the corresponding activity of some of their metabolites has also been examined. The major metabolite of pentachlorophenol in mice and rats, tetrachloro-7 ora-hydroquinone, induced mutations in the hprt locus (but not the ouabain-resistance locus) of V79 Chinese hamster cells (Jansson Jansson, 1991), covalent damage (including 8-hydroxyguanine) in naked DNA in the presence of Cu(Il) (Naito et al., 1994), DNA strand breaks and accumulation of p53 in NIH 3T3 cells in vitro and transfonnation of mouse embryo fibroblasts in a two-stage model (Wang et al., 1997). The same metabolite, as well as tetrachloro-1,4-benzoquinone and tetrachloro-l,2-benzoquinone, caused DNA strand breaks in V79 Chinese hamster cells (Dahlhaus et al., 1996). 

Another study found that low doses of ouabain did not modify the acute heat pain latency, but higher doses caused excitation and motor impairment, suggesting that ouabain does not produce a pronounced effect on the pain threshold (Horvath et al., 2003). It is supposed that the controversial results might be due to the fact that ouabain produces its effect on all of the cells, inasmuch as all have Na, K -ATPase, and its net effects on transmitter releases might be dose-dependent. 

Among the other mechanism of action tested it was recently found that palytoxin caused efflux in an hybrid between the Na-K-ATPAse and the H-K-ATPase, converting this enzyme into and open channel (Farley et al. 2001). Furthermore, palytoxin stimulated a cation-dependent current in rat distal and proximal colon in a concentration-dependent manner when applied to the mucosal surface of the tissue whose apical membrane does not express Na-K-ATPase. The observation that the palytoxin-induced current was blocked by vanadate but was resistant to ouabain supported the suggestion that the toxin was able to convert a vanadate-sensitive H-K-ATPase into an electrogenic cation transporter and, consequently, that the pore-forming action of palytoxin was not restricted to Na-K-ATPase since it was also observed with the colonic H-K-ATPase (Scheiner-Bobis et al. 2002). The toxin was also found to interfere with the sarcolemmal Ca pump in cardiac myocytes (Kock-skamper et al. 2004). 

Between October 30 and November 4, 2000, 11 persons were intoxicated due to ingestion of a serranid fish Epinephelus sp. in Kochi Prefecture, Japan. Their symptoms included severe muscle pain, low back pain, and discharge of black urine. The causative agent was identified as palytoxin on the basis of delayed haemolytic activity, which was inhibited by an anti-palytoxin antibody and ouabain (Taniyama et al. 2002). Although the toxic dose of palytoxin in humans could not be determined, extrapolation of the data available in animals will give a toxic dose in a human of about 4 pg. This fact places palytoxin among the most toxic nonproteinic animal toxins known to date (Taniyama et al. 2002) however, its mechanisms of toxicity remain to be elucidated. 

Interest in the antiarrhythmic activity of quaternary ammonium compounds continues. Unlike bretylium (11a). its o-iodobenzyl trimethyl-ammonium analog (UM-360, lib) did not inhibit release of norepinephrine from sympathetic nerve endings and did not cause adrenergic stimulation on its own.UM-36O effectively antagonized ventricular arrhythmias produced by ouabain in dogs, an action bretylium did not possess. Both agents elevated the threshold to electrically induced ventricular fibrillation. The same group of workers also studied the profile of a quaternary propan-2-ol derivative (UM- 2h, 12). ° In contrast to tertiary compounds of... 

R-8I8 (17) prevented chloroform-induced ventricular fibrillation in mice as well as arrhythmias caused by hydrocarbon-epinephrine, ouabain, aconitine and coronary occlusion in dogs.5° The activity of numerous analogs in the mouse chloroform test has been described.57... 

Noebe/s That is an interesting question, but I don t know the answer. High doses of these drugs tend to cause seizures by poisoning the Na + pump. It bears investigation. There are a number of drugs that make people with epilepsy worse, and ouabain would be one of them, particularly in these individuals. 

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