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1. In guinea-pig aorta, removal of external K produced contraction which reached maximum (about 1 g) after about 3 h. Excess K (65.4 mM) produced contraction (about 1 g) at a faster rate of increase than was observed in K-free solution. 2. Verapamil, nifedipine and diltiazem (10−7–10−5 M) and the raising of [Mg]0 (8–32 mM) had no effect on the contraction induced by K-free solution, although they relaxed the contraction induced by high-K solution. Verapamil (10−6 M) also relaxed the contractions induced by other depolarizing agents, TEA (40 mM) and Ba (15 mM). 3. Following incubation in Ca- and K-free solution for 3 h, the readdition of Ca produced contraction at a faster rate of increase than in a K-free normal Ca containing solution. Verapamil (10−6 M) and Mg (16 mM) had exhibited little effect on these Ca-induced contractions. The Ca-induced contractions in high-K solution, on the other hand, were significantly suppressed in the presence of verapamil (10−6 M) and Mg (16 mM). 4. After incubation of the muscle in K-free solution for 1 h, Na depletion caused a more rapid and greater contraction than was seen in untreated muscle. This tension development was also unaffected by verapamil (10−6 M) and Mg (16 mM). 5. Substitution of Sr for Ca produced contraction in K-free or high-K solution. Sr-induced contraction in K-free solution was scarcely affected by verapamil (10−6 M), while Sr-induced contraction in high-K solution was inhibited. 6. 45Ca entry into smooth muscle during the contractions was measured by the modified “La method”. The 45Ca uptake was markedly increased both in K-free and high-K solutions. Verapamil (10−6 M) and Mg (16 mM) had no significant effect on the 45Ca uptake increase clicited by K-free solution, whereas they significantly inhibited the 45Ca uptake increased by high-K solution. 7. It is suggested that the contraction induced by K-free solution is initiated by a mechanism different from that underlying the depolarization-induced contraction, and that it is produced by an influx of Ca through Na-Ca exchange mechanism. The data also suggest that the Ca binding site on the Na-Ca exchange carrier is occupied by Sr ions but not by Mg ions. It is likely that such a carrier system is not influenced by organic “Ca antagonists”.

1 Several putative calmodulin antagonists have been examined for their inhibitory action on muscle tension and cellular Ca content in the K-depolarized vascular and intestinal smooth muscles. 2 The 65.4 mM K-induced sustained contraction in the media-intimal layer of rabbit aorta and the 45.4 mM K-induced sustained contraction in guinea-pig taenia coli were inhibited by the calmodulin antagonists, prenylamine, chlorpromazine, N2-dansyl-L-arginine-4-t-butylpiperadine amide (No. 233), and N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide (W-7), and also by the organic Ca antagonists, verapamil and diltiazem. 3 The cellular Ca content in rabbit aorta and guinea-pig taenia coli as measured by a modified lanthanum technique increased in the high-K solutions. The increments were inhibited by these antagonists at concentrations similar to those required to inhibit the K-induced contractions. However, W-7 did not change (in aorta) or only slightly decreased (in taenia coli) the K-induced increase in the cellular Ca content. 4 A high concentration (2 X 10(-4)M) of W-7 increased the resting cellular Ca content without increasing the muscle tension in aorta. The increment was inhibited by verapamil, sodium nitroprusside or hypoxia (N2 aeration). 5 It is suggested that the inhibitory effects of prenylamine, chlorpromazine and No. 233 may be attributed mainly to the Ca antagonistic effect whereas W-7 may inhibit the process beyond the transmembrane Ca influx.

A transport mechanism of methylmercury to egg albumen was investigated in laying Japanese quail which had received a single intravenous injection of 203Hg-methylmercuric chloride. Whole body distribution of 203Hg was analyzed by means of autoradiography. It was notable that the uptake of 203Hg was higher in the oviduct than in any other tissue checked. Further, the 203Hg was detectable in egg albumen which had been synthesized and secreted in the magnumean portion of the oviduct. From the observations mentioned above, it is suggested that methylmercury in the vascular system was taken up cumulatively by the oviduct and deposited in egg albumen by the secretory way. On the tissue level of the benzene-extractable form of 203Hg compounds (RHg) quantitative analysis was made in the respective organs. RHg decreased from the blood and liver with the lapse of time. The renal level of RHg showed a gradual increase which was followed by a rapid decrease. In contrast to the tissue tested above, a magnumean uptake of RHg increased gradually and reached the highest level of the four tissue after 24 hours. The RHg content was analyzed in the egg shell, albumen and yolk. It was the largest in the albumen and second largest in the yolk, but negligible in the shell. In 7 eggs laid over a period of 8 days after the injection, the total RHg content was approximately 44% of the dose of the radiocompound administered. The largest amount of RHg was found in the albumen of an egg the third in the order of oviposition after the injection. The fecal and urinary content of 203Hg was approximately 23% of the dose during the same period of time. These quantitative data suggest that the major part of methylmercury in the body is transported into egg albumen via the secretory mechanism of the magnumean portion of the oviduct. Starch gel electrophoresis of the soluble cytoplasmic fraction of the magnumean homogenate and of egg albumen revealed that 203Hg was associated with protein bands which had migrated near the front. The protein bands were considered to be ovalbumin. It was confirmed from an examination in vitro that 203Hg-methylmercuric chloride bound to a purified hen's ovalbumin preparation. These results mentioned above suggest that methylmercury is readily bound to ovalbumin which was newly synthesized in large quantity in the magnumean portion of the oviduct.

The effects of vanadate (Na3VO4) on the contractions induced by high concentrations of K, histamine and norepinephrine in isolated guinea-pig aorta were investigated. Vanadate (10(-3) M) relaxed the high K contraction only when the external K concentration was above 85.4 mM. Vanadate showed no inhibitory action on the contraction induced by either Na-containing 45.4 mM K solution or Na-poor 45.4 mM K solution. Ouabain (2 X 10(-5) M) had no inhibitory effects on the contractions induced by these high K solutions. Vanadate failed to relax the contraction induced by histamine or norepinephrine in normal (5.4 mM) medium, while it inhibited the contraction in the presence of 142.2 mM K. Ouabain also did not inhibit the histamine- or norepinephrine-induced contraction in either normal or high K solution. These results suggest that the inhibitory actions of vanadate are not due to an inhibition of Na pump and that these effects depend on the presence of a high concentration of external K ions.

Papaverine (Pap) inhibited a tonic tension development in guinea pig taenia coli induced by an elevation of the potassium concentration of the medium to 40 mM (40-K). The ID50 of Pap was 4.5 × 10-6 M. Inhibition of the 40-K induced tonic tension by Pap was dependent on the calculated concentration of non-ionized form, but not the ionized form. Inhibition of the tonic tension by Pap and various metabolic inhibitors was not antagonized by raising the Ca++ concentration in the medium. Results obtained from simultaneous measurement of the 40-K induced O2 consumption and tension illustrated that the inhibition of O2 consumption rapidly induced the inhibition of the tension. Furthermore, glucose removal, amytal or Pap resulted in a progressive relationship between the inhibition of O2 consumption and the inhibition of tension. The inhibition of Pap as determined by O2 consumption was not reversed by application of 10-4 M 2,4-dinitrophenol (DNP). These results plus graphical analysis of the mechanical response suggest that Pap may penetrate the cell membrane and inhibit mitochondrial respiration, thereby inhibiting this very respiration-dependent contracture.

In previous publications it was reported that barium in concentrations from 0.5 to 20 mM induced tension development in isolated guinea pig taenia coli, which response was dependent on the presence of external calcium (1), and that total Ca content did not change but 45Ca uptake of the cellular fraction which did not exchange within 4 minutes increased above control level during Ba-induced tension development (2). It was also mentioned that Ba increased Ca entry in taenia coli and that this Ca probably plays an essential role during tension development (2). On the other hand, hypertonically added 40 mM K-induced tonic tension development in taenia coli was noted to be composed of phasic and tonic phases and it was proposed that in the phasic contraction, sufficient Ca is released from a cellular site to initiate contraction, whereas in the tonic contraction enough Ca crosses the membrane to initiate and also to maintain contraction(3). However, the movement of Ca in the above processes has not been studied systematically. This work was undertaken to study the movement of Ca in taenia coli during Ba- and high-K-induced tension developments by investigating the total Ca, 45Ca uptake and efflux and 45Ca uptake of the cellular fraction which did not exchange within 4 minutes. A part of this work has already been reported (2, 4).

1. Maltoxin isolated from the malt rootlet of Hordeum distichon, L., growing in Japan was identified as candicine (p-hydroxy-β-phenylethyltrimethylammonium base) in the form of chloride and picrate.2. Amount of candicine in two kinds of “malt sprouts” made from H. distichon, L., growing in Japan and H. hexastichon, L., being native to Japan was estimated by bioassay on the frog muscle after separation of the base by paper chromatography.

The mode of action of tetrodotoxin on the frog muscle fiber membrane has been analyzed with the aid of intracellular microelectrodes. Tetrodotoxin of 10–7 concentration made the applied cathodal current ineffective in producing action potential, whereas the resting potential and resting membrane resistance underwent little or no change. With 10–8 tetrodotoxin the muscle fibers responded with the small action potentials at high critical depolarizations. These results can be explained on the basis of the membrane being stabilized by inactivation of the sodium-carrying mechanism. Although delayed rectification was not observed in normal muscle fibers, it became apparent in the fibers rendered inexcitable by tetrodotoxin. This finding, together with other evidence in the existing literature, supports an applicability of the sodium theory to the frog muscle fibers.

It was reported that an application of high-K (isotonic, 40 mM) caused an increase in oxygen consumption accompanied by an increase in tension change in guinea pig taenia coli (1) and that these changes were reversibly abolished by a depletion of Ca from the high-K medium and Sr could replace Ca only for oxygen consumption (2). These results suggest that Ca entering smooth muscle treated with high-K probably increases oxygen consumption, independent of an increase in muscle tension. In a previous paper (3), effects of factors inhibiting tension development on oxygen consumption of the muscle in high-K medium were reported. Glucose removal from the high-K medium abolished the already developed tension corresponded with a decrease in the elevated oxygen consumption rate. Addition of DNP (1×10-4M) to high-K medium further increased or maintained the increased oxygen consumption although it abolished the already developed tension, and the change in oxygen consumption was not modified by Ca removal. On the other hand ouabain (2.5×10-6 M) maintained the increased oxygen consumption in high-K medium, but almost abolished the developed tension. The increase in oxygen consumption was dependent on external calcium. In the present paper, effects of factors inhibiting high-K induced tension and/or oxygen consumption on Ca distribution in taenia coli are studied and this throws some light on a participation of Ca distribution in changes in tension and oxygen consumption of the muscle in high-K medium. A study on ouabain and DNP with high-K on Ca exchange in taenia coli has been reported by Pfaffman and Holland (4), which is incompatible with the present data.

In smooth muscle of guinea pig taenia coli, showing spontaneous activity, the curves of rhythmic changes in muscle tension appears parallel to the curves of changes in Po2 level in the medium (1-3). On the other hand, Saito et al. (3) reported that an application of high K (isotonically, 40 mM) caused an increase in oxygen consumption accompanying increase in tension change in taenia coli, and that this was in accordance with the concept (4, 5) that the K-induced tonic response resulted from a transmembrane transport of Ca that depended on the aerobic breakdown of carbohydrates. In the present paper, effects of Ca depletion on the oxygen consumption accompanying muscle tension change both spontaneous and that induced by high K were studied, and a dissociation of the changes in oxygen consumption and muscle tension change was attempted by substituting strontium (Sr) for Ca in the external medium. Some of the results have already been reported (6, 7).

In a previous report (1) it was shown that in guinea pig taenia coli hypertonically added 40 mM K induced a large tension and that both tissue Ca and 45Ca uptake of the muscle measured after a 4 minutes wash increased, while in 152 mM K/0 mM Na medium only a small tension remained and 45Ca uptake did not increase while tissue Ca decreased. It has also been shown that the tonic response in hypertonic 40 mM K medium is dependent on aerobic breakdown of carbohydrates and blocked by sodium transport inhibitor (2-4). The tonic response in 152 mM K/0 mM Na medium was however shown to be unaffected by a sodium transport inhibitor and not solely dependent on aerobic breakdown of carbohydrates (4). The present investigation is concerned with the changes in tension, uptake of 45Ca measured after a 4 minutes wash and tissue Ca in varying concentrations of Na and K in the external medium, and also the effects of inhibitors of metabolism and sodium transport in guinea pig taenia coli. A part of this work has already been represented (5).

Palytoxin (PTX), a highly toxic and sugar-containing substance isolated from Palythoa tuberculosa, caused K+ release from rabbit red blood cells. Cardiac glycosides, such as ouabain, convallatoxin, cymarin, digoxin and digitoxin, inhibited the PTX-induced K+ release. Their corresponding aglycones did not inhibit the K+ release, but antagonized the inhibitory effect of the glycosides. All these cardiotonic steroids equally inhibited the activity of (Na+ + K+-ATPase prepared from hog cerebral cortex. These results suggest that the sugar moiety of the cardiac glycosides is important for the inhibitory effect on the K+ release induced by PTX and that the inhibition is not related to their inhibitory potency on the (Na+ + K+)-ATPase activity.

Palytoxin (PTX) caused K+ release from rabbit erythrocytes at a concentration as low as 10−11 M. The K+ release due to PTX at a concentration below 10−9 M was dependent on Ca2+ in medium. The effect of Ca2+ was substituted fully by Sr2+ and partially by Ba2+. W-7 (2 × 10−4 M), a known inhibitor of calmodulin, markedly inhibited the rate of K+ release due to PTX. W-5 (2 × 10−4 M), an analog of W-7 with lower affinity to calmodulin than W-7, showed weaker inhibition. Other calmodulin antagonists, such as prenylamine, chlorpromazine and compound 48 80 , also inhibited the PTX-induced K+ release. These results suggest that the K+ release induced by PTX involves the process(es) mediated by intracellular Ca2+ and calmodulin.

The effects of the Na+ ionophore monensin on contractile responses were investigated in guinea-pig aorta in normal and high K+ solutions. In normal K+ (5.4 mM) solution, monensin (2 × 10−5 M) produced a rapid increase in tension followed by slow relaxation. This contraction was markedly inhibited by phentolamine (10−5 M) or prazosin (10−6 M) and was accompanied by an increase in tritium efflux from tissue preloaded with [3H]norepinephrine. In the presence of phentolamine, monensin (1–2 × 10−5 M) or ouabain (1−2 × 10−5 M) caused only a small and slowly developing contraction. Simultaneous application of these agents caused a more rapid and greater contraction. Either monensin or ouabain gradually increased cellular Na+ and decreased cellular K+ content. When monensin was applied simultaneously with ouabain, there was a rapid increase in cellular Na+ and loss of cellular K+. In high K+ (65.4 mM) solution, monensin (10−6 M) slightly reduced the increased tension level but when external glucose was omitted monensin markedly inhibited the contraction. A significant decrease in tissue ATP content was observed only when monensin was applied in glucose-free solution. Similarly, hypoxia (N2 bubbling) markedly inhibited the high K+ contraction and decreased the tissue ATP content only in the absence of glucose. These results suggest that monensin produces a neurogenic contraction due to the release of endogenous catecholamines and also produces a myogenic contraction by a decrease in transmembrane Na+ and K+ gradients when the Na+ and -K+ pump is inhibited by ouabain, and that monensin inhibits aerobic energy metabolism of vascular smooth muscle.

The inhibitory effects of nicorandil, nitroglycerin and isosorbide dinitrate on the contractions induced by 10(-6) M norepinephrine or by 65.4 mM K+ were compared in the vascular smooth muscle of rabbit aorta. These compounds relatively selectively inhibited the contraction induced by norepinephrine. Norepinephrine induced a sustained contraction in the aorta depolarized with high K+ and treated with 10(-6) M verapamil, and this contraction was also inhibited by these compounds. The increase in Ca2+ influx induced by norepinephrine, but not by high K+, was inhibited by the three compounds. The norepinephrine-induced transient contraction, which is due to release of stored Ca2+, was inhibited by these compounds. The inhibitory effects of nicorandil and nitroglycerin on this contraction were attenuated by high-K+ depolarization. Methylene blue (10(-5) M) antagonized and M&B 22948 (10(-5) M) potentiated the inhibitory effects of these compounds. These results suggest that nicorandil, nitroglycerin and isosorbide dinitrate have a similar mechanism of action. These compounds inhibit the norepinephrine-induced sustained contraction possibly by inhibiting the Ca2+ influx through receptor-linked Ca2+ channels, and inhibit the transient contraction by membrane hyperpolarization and also by direct inhibition of Ca2+ release although other mechanism of action may also be involved.

Palytoxin (PTX), at extremely low concentrations (0.01-1 nM), caused K+ release from rabbit erythrocytes. Among the various chemical compounds tested, cardiac glycosides potently inhibited the PTX-induced K+ release. The order of inhibitory potency (IC50) was cymarin (0.42 microM) greater than convallatoxin (0.9 microM) greater than ouabain (2.3 microM) greater than digitoxin (88 microM) greater than digoxin (90 microM). Their corresponding aglycones, even at 10 microM, did not inhibit the K+ release, but competitively antagonized the inhibitory effect of the glycosides. All these cardiotonic steroids inhibited the activity of (Na+ + K+)-ATPase prepared from hog cerebral cortex in narrow concentration ranges (IC50 = 0.15-2.4 microM), suggesting that the inhibition of K+ release is not related to their inhibitory potency on the (Na+ + K+)-ATPase activity, and the sugar moiety of cardiac glycosides is involved in the inhibition. On the other hand PTX, at higher concentrations (greater than 0.1 microM), inhibited the (Na+ + K+)-ATPase activity. However, this inhibitory effect of PTX was not antagonized by ouabain. It is suggested that, compared with ouabain, PTX has additional binding site(s) on the (Na+ + K+)-ATPase.

The properties of contractions induced by ouabain and by K depletion were studied in comparison with those induced by other stimulants in guinea pig taenia coli. Ouabain 7.5 X 10(-6) M and K depletion produced biphasic contractions with similar time courses. Both contractions were slightly inhibited by low (0.25 mM) and high (7.5 mM) Ca concentrations, while the high K contraction was strongly inhibited by low Ca and potentiated by high Ca. Contractions induced by ouabain and K depletion were highly sensitive to lowering of the temperature and abolished at 15 degrees C, although contractions induced by carbachol 1.1 X 10(-7) M and histamine 5 X 10(-7) M were still observed below 15 degrees C. In Cl deficient solution substituted by SO4 or propionate, contractions induced by ouabain and K depletion were potentiated, while contractions induced by high K, carbachol and histamine were suppressed. These results indicate a striking similarity between contractions induced by ouabain and K depletion suggesting a common mechanism for both contractions.

Effects of atropine (ATR, 0.5 mg/kg, i.v.), proglumide (PGM, 100 mg/kg, i.v.)and metiamide (MTM, 0.4 mg/kg, i.v.) on gastric acid secretion induced by vagal stimulation, carbamylcholine (CCh, 5μg/kg, i.v.), tetragastrin (TG, 5μg/kg, i.v.) and histamine (Hist, 10μg/kg, i.v.) injections were examined by means of continuous pH recording of proventricular effluent in urethan anesthetized chickens. Birds were operated for fitting an esophageal cannula and gastric fistel, artificial respiration, bilateral vagotomy and instillation of physiological saline solution. Electrical stimulation (0.1msec duration, 30volts, 50 Hz, for 40 to 60 sec) was applied to Trunks communis n. vagi at the proximal region of the proventriculus where the proventricular rami (Rr. gastrici glandulares) branched. The vagal stimulation and the administration of CCh produced a biphasic profile of pH fall response consisting of an early transient and a secondary lasting phases. The transient response was larger in the degree of pH fall than the lasting one, and was inhibited by ATR but not by PGM and MTM. The lasting response was reduced by all of the three inhibitors. PGM and MTM inhibited pH fall responses induced by TG and Hist, respectively. These results show that the vagally stimulated acid secretion consists of an early transient response which is major component and a secondary lasting response Which is minor component. It is suggested that the transient response is directly mediated by cholinergic transmission and the lasting response is possibly mediated by endogenous gastrin and histamine in the pathways sensitive to PGM and MTM.

Effects of palytoxin (PTX) on isolated papillary muscles of guinea pigs were studied in an attempt to elucidate the mechanical and electrical activities. Inotropic effects of PTX above 3×10−9 g/ml were; an early positive inotropic effect, slowly developing contracture accompanied by decline in phasic tension, appearance of aftercontractions and arrhythmias at high doses. The positive inotropic effect of PTX was enhanced in high Ca2+ medium but was not modified by propranolol. PTX induced a sustained depolarization and decrease in the amplitude, upstroke velocity and duration of action potential. During development of depolarization, arrhythmias occurred, which lasted for 5–10 min and reappeared 30–60 min after. Oscillatory afterpotential often appeared. Neither reserpine nor practolol prevented the PTX-induced arrhythmia while propranolol prevented it. Tetrodotoxin slowed the development of depolarization due to PTX and inhibited PTX-arrhythmias. In low Na+ medium, PTX exerted fewer effects on resting and action potentials and produced no arrhythmia. The results suggest that PTX-induced depolarization is responsible for the generation of contracture and arrhythmia and that the depolarization is due to the change in membrane Na permeability.

Experiments were designed to assess the mode of action of palytoxin (PTX), isolated from Palythoa tuberculosa, on mechanically denervated rabbit aortic strips. PTX induced a sustained contraction in the muscle dose dependently. The contraction was irreversible. In the depolarized aorta, PTX did not induce a contraction whereas norepinephrine (NE) did. Removal of calcium from the bathing medium prevented PTX and high K+ contractions, whereas phasic responses were elicited by NE. D600 also inhibited the contraction induced by PTX or high K+ but had a lesser effect on that induced by NE. Sodium nitroprusside inhibited only the effect of NE. PTX increased dose dependently the 45Ca uptake of a fraction not removable by La3+ treatment and the increase was inhibited by D600. High K+ also increased the 45Ca uptake although NE did not. It is suggested that PTX increased Ca2+ influx into the smooth muscle cell to cause a contraction, which may be analogous to the action of high K+.

Effects of the toxic component of jellyfish (Carybdea rastonii) (pCrTX) on the smooth muscle tension of isolated rabbit thoracic aorta were examined. pCrTX, at concentrations higher than 10(-7) g/ml, caused slowly developing tension that reached its maximum after about 1 hr. This contraction was partially inhibited by pretreatment of the tissue with phentolamine (5 X 10(-6) M) or indomethacin (10(-5) M). The contraction induced by pCrTX was partially inhibited by nicardipine (10(-7) M) and markedly augmented by Bay k8644 (10(-6) M). In low-Na+ solution, the rate of rise of the pCrTX-induced contraction was significantly reduced. Removal of external Ca2+ inhibited the pCrTX-induced contraction by about 30%, while chlorpromazine, trifluoperazine, prenylamine and papaverine (10(-4) M) completely inhibited the contraction. pCrTX itself did not cause any contraction in saponin-skinned smooth muscle and had no effect on the Ca2+-induced contractile tension. It has been reported that pCrTX-induced contraction is attributable to the release of endogenous catecholamines and also to the increase in Ca2+ influx in smooth muscle (Azuma et al., 1986). The present results confirmed the previous suggestion and further suggested that a portion of the contraction is due to release of prostaglandin(s) and also to the direct effect on smooth muscle which is not dependent on Ca2+ influx.

In Ca-deficient smooth muscle of guinea-pig taenia coli, repeated application of high-K solution (45.4 mM) containing Ca induced contractions of similar shape and magnitude. In muscle treated by a Ca- and Mg-deficient solution, however, addition of Ca and K either did not induce contraction or induced only a delayed contraction. Ouabain (1×10−3 M) also inhibited Ca- and K-induced contraction. Na content of taenia coli smooth muscle increased and K content decreased during incubation in Ca- and Mg-deficient solution. Ouabain produced similar, but smaller, changes in Na and K contents. Contractility of Ca- and Mg-deficient taenia partially recovered if the muscle was treated with Na-deficient solution which resulted in a large decrease in Na content. Similar treatment produced only a small decrease in Na content in ouabain-treated taenia, and contractility did not recover in these muscles. Application of hyperosmotic NaCI (160 mM) decreased tissue weight in both control and ouabain-treated taenia. In muscle treated with Ca- and Mg-deficient solution, however, hyperosmotic NaCI application had little effect on tissue weight. Following pretreatment of muscle with Ca- and Mg-deficient solution (containing 2 mM EDTA) for 2 hr, graded contractions were induced by cumulative application of Ca between 10−7 to 10−6 M in the presence of Mg and ATP. It is concluded that Ca- and Mg-deficient solution increases membrane permeability and also abolishes transmembrane gradients of Na and K in guinea pig taenia coli.

Effects of pretreatment with selenate, as well as selenite, on the retention of 203Hg in male and laying Japdnese quail were investigated. Birds were killed 24 hOuTs after a single intravenous injection with 203Hg-mercuric nitrate. The radioelement increased in concentration in most of the tissues checked, especially in the blood corpuscle fraction and liver, in the birds had been treated with both selenium compounds than in the controls. On the other hand, the pretreatment decreased the concentration of 203Hg ill the kidney of both sexes of birds and ova of laying ones. In the brain uptake of 203Hg was little affected by the pretreatment which caused a reduction of fecal and urinary excretion of the radiomercury. The selenium-response patterns in the pretreated birds was not altered by the sex of birds and the type of selenium compound used. The results obtained in Japanese quail agreed well with those reported in mammals treated with selenite.

In Ca-free solution norepinephrine (NE) produced only a phasic contraction in the media-intima layer of rabbit aorta. The second application of NE was almost ineffective. Incubation of the muscle with Ca for a short period (Ca loading) restored the ability to produce a phasic contraction in Ca-free solution. Various ions and compounds were applied to the muscle prior to the Ca loading or prior to NE application and it was found that these treatments variously affected the NE-induced phasic contraction. The data suggest that the NE-induced phasic contraction in Ca-free solution results from Ca release from cellular sites and that a hyperbolic relationship exists between the amount of Ca at these sites and the magnitude of the contraction. These sites take up extracellular Ca by a process sensitive to La 3+ but not to D600; the Ca influx stimulated by high K solution, which is sensitive to D600 also contributes to refilling of these sites; NE releases this stored Ca by a process sensitive to procaine, caffeine and theophylline and, in this manner, elicits a phasic contraction.

Nagase, H., Karaki, H. and Urakawa, N. The inhibitory effects of calmodulin antagonists on the endothelium-dependent relaxation in rabbit aorta . Japanese Journal of Smooth Muscle Research 1986, 22 (2), 97-102 .-Effects of trifluoperazine (TFP, 10-5 M), trifluoperazine sulfoxide (TFP-SO, 10-5 M), N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7, 10-4 M), N-(6-aminohexyl)-1-naphthalenesulfonamide (W-5, 10-4 M) and verapamil (10-5 M) on the endothelium-dependent relaxation of the contractions induced in the isolated rabbit aorta were studied . Carbachol (10-6-10-5 M) and A23187 (10-8 M) relaxed the contraction due to norepinephrine (10-6 M) and histamine (10-5 M) in the aorta with endothelium. TFP and W-7 completely inhibited the relaxation induced by carbachol and A23187. In contrast, TFP-SO and W-5, which have lower affinity to calmodulin, had little or no effect on either the carbachol- or A23187-induced relaxation . An organic calcium antagonist, verapamil, did not change the relaxation induced by carbachol or A23187. W-7 did not modify the relaxing effect of sodium nitroprusside (10-8-10-6 M) which is not mediated by endothelium. These results suggest that either formation or release of endoth -elium-derived relaxing factor involves the process mediated by calmodulin in the rabbit aorta.

1. 1. A toxic component (pCrTX) of jellyfish Carybdea rastonii (10−8−10−6 g/ml) caused a contraction in both rat aorta and guinea-pig taenia coli which was partially inhibited by indomethacin or aspirin. 2. 2. pCrTX (10−7−10−6 g/ml) relaxed the norepinephrine-induced contraction in rat aorta which was inhibited by removing endothelium or by adding methylene blue. 3. 3. These results suggest that a portion of the pCrTX-induced contraction is due to release of prostaglandin(s) and that the pCrTX-induced relaxation is due to release of an endothelium-derived relaxing factor.

During the course of the survey of causes of ciguatera poisoning, a pharmacologically very active substance was obtained from the zoanthid (Coelenteratd), Palythoa tuberculosa Esper (Kimuraet al., 1972; Kimura and Hashimoto, 1973) found in the digestive tract of a filefish, Alutera scripta, one most widely re puted as ciguatoxic in the tropical and subtropical regions (Hashimoto et al. 1969). This substance has been found to be selectively distributed in female polyps of the zoanthid, especially concentrated in their matured stage (Kimura et al., 1972). The lethal dose of this substance has been estimated to be 0.6 µg/ kg in mice when intraperitoneally injected (Kimura and Hashimoto, 1973). This toxicity far exceeds that of tetrodotoxin or saxitoxin, and may even exceed that of batrachotoxin, the most potent of natural toxins of low molecular weight ever known (Daly et al., 1965). This substance, here designated as palythoatoxin, has been reported to be very similar, if not identical, to palytoxin previously isolated by Moore and Scheuer (1971) from closely related Palythoa species (P. vestitus and P. toxica) (Kimura and Hashimoto, 1973). The latter reportedly has an estimated molecular weight of about 3300, is not a polypeptide or a protein nor does it contain sugar, and has lethal doses of 0.4 µg/kg (i.p.) and 0.15 µg/kg O-v.) in mice (Moore and Scheuer, 1971; see also Sheikh, 1970).

This study deals with the effects of monensin, a Na ionophore, on contraction, cellular Na content, oxygen consumption and tissue ATP content of smooth muscle of the guinea-pig taenia coli depolarized by high K (62.7 mM) solution. The application of monensin (10(-8) -10(-6) M) had little effect on the phasic component of the K contraction while it decreased the tonic component. The inhibitory effect of monensin, unlike that of verapamil, was not antagonized by raising the concentration of external Ca. Under hypoxic conditions, the inhibitory action of monensin (10(-7) M) was greatly reduced. The removal of Na (choline or sucrose substitution) from the high K solution did not attenuate the inhibitory effect of hypoxia or monensin. Monensin (10(-7) M) produced only a small increase in cellular Na in the depolarized muscle. The K-induced increase in the rate of oxygen consumption was suppressed by monensin (10(-6) M). In high K solution, but not in normal solution, monensin (10(-6) M) decreased the tissue ATP content. These results suggest that the relaxing action of monensin is mainly due to the inhibition of aerobic energy metabolism of the smooth muscle of guinea-pig taenia coli.