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The effect of caffeine on contractile activity and Ca movement was investigated in guinuEa pig taenia coll. Caffeine at a concentration of 7 mM produced a contraction for approx. 7 min and increased 45Ca influx and efflux without a change in Ca content in the tissue. The effect of caffeine on Ca movement was the same as that of carbachol in the early phase of the contractile response. The caffeine-contraction was not potentiated by an addition of Ca up to four times that of normal concentration, however, the carbachol-contraction was potentiated. When the muscle was soaked in a Ca-free solution, it showed “Ca-free contraction” and a loss of the tissue Ca content. When caffeine was added immediately after the “Ca-free contraction” was relaxed, caffeine produced a transient contraction and increased the loss of the tissue Ca content. Under identical circumstances, carbachol did not induce a contraction or affect the Ca content of the tissue. In conclusion, caffeine was demonstrated to increase Ca exchangeability in smooth muscle cell as did carbachol, however, the results suggested the possibility that caffeine releases a bound Ca in the cell for contraction whereas carbachol induces a contraction by an increase in a permeability of the cell membrane to Ca ions.

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).

In the preceding articles (1-4), a dual mode of paralyzing action of candicine (maltoxin) on the frog muscles was reported, i.e., an overall depolarization of the muscle fiber membrane and a depression of sensitivity of the endplate membrane to acetylcholine. On the other hand, candicine has been known as a nicotine-like drug without any detail analysis (5-17). Present experiments have been carried out to elucidate the mode of the ganglion stimulating action of candicine in comparison with some other ganglionic stimulants.

Maltoxin, an amine obtained from brew malt rootlet, has been reported to have a strong contrac ile effect on the frog rec us muscle (1). Crystalline powder of maltoxin hydrochloride was isolated from the crude component, and was found to produce a peripheral paralysis in the frog. This peripheral action of maltoxin was revealed to be an effect on the neuromuscular junction. In the present paper the effect of maltoxin on the nerve-sartorius and the rec us muscle preparations of the frog is described.

Maltoxin, an amine obtained from brew malt rootlet, causes a neuromuscular block in the frog. Its mode of action on the frog's sartorius muscle has been studied mainly with the aid of intracellular microelectrodes. Maltoxin of 10–5 concentration caused an over-all depolarization of the muscle fibers; therefore, direct and indirect stimulations of the muscle were ineffective in producing muscle action potential. Progressive repolarization took place thereafter and the muscle became excitable by direct stimulation, though indirect stimulation remained ineffective for a long period of time. Small end-plate potentials observed could not be explained in terms of depolarization. It was found that the sensitivity of the end-plate membrane to acetylcholine was effectively depressed by maltoxin, and that this is responsible for the persistent neuromuscular block. The initial over-all depolarization caused by maltoxin was fairly antagonized by a previous treatment with d-tubocurarine. It is concluded that maltoxin has a dual mode of action, having some resemblance to acetylcholine, decamethonium, succinylcholine and nicotine.

In the previous paper (1), it was reported that HCl-ethanol extract obtained from wheat gluten malt rootlet exhibited potent toxicity against mouse. In connection to the finding, further experiments have been carried out employing brew malt rootlet as a test material. As it has been known, the rootlet contains various amines, such as hordenine, choline, betaine, tyramine and N-methyltyramine, some of which exert certain pharmacological activities (2-10). During the course of our present studies, another amine was found in the HCl-ethanol extract of the brew malt rootlet. Differing from other amines noted, the amine, named “maltoxin, ” was revealed to exhibit a strong contractile activity on the rectus muscle of frog. In this paper the method of preparation and some of the chemical and pharmacological properties of this active principle are described.

It was reported that high-potassium (K) solution produced a contracture (K-induced contracture) in the guinea pig taenia coli, and the tension development in the muscle depolarized with high-K was dependent on calcium (1, 2), and that 45Ca uptake and exchangeable fraction of cellular Ca increased with high-K (2). Furthermore, it was demonstrated that K-induced contracture was composed of phasic and tonic phases and was proposed that in the phasic contraction, sufficient calcium was released from a cellular site to initiate contraction, whereas in the tonic contraction, enough calcium crossed the membrane to initiate it and that the transmembrane calcium transport involved in the latter response was dependent on metabolism (3). On the basis of these results, the role of metabolism in the K-induced contracture of taenia coli was examined by the use of various metabolic intermediates, inhibitors of metabolism and active transport, revealing that the factors such as substrate removal, a decrease of temperature, DNP, ouabain and a substitution of external sodium chloride with lithium chloride abolished the tonic response whereas the same factors had little or no effect on the phasic response. Hence it was considered that the phasic response was a passive process, while the tonic contraction was an active one depending on metabolism and possibly linked to active Na transport (4). This consideration was also supported by the electrophysiological experiments (5). In the present paper, further evidence was obtained concerning to the influences of the physiological components in the external media, that is, magnesium chloride (MgCl2), sodium bicarbonate (NaHCO3) and sodium phosphate (NaH2PO4) on the K-induced tension development of taenia coli.