S.L. Friess

Further studies on biological actions of steroidal saponins produced by posionous echinoderms

Abstract Purified samples of two steroidal saponins produced by the starfish Asterias amurensis Lutken have been studied with respect to potency in irreversible blockade of contractural responses from the rat phrenic nerve-diaphragm preparation. The first, Asterosaponin A, is relatively more potent in blockade of indirectly elicited contraction (N-twitches) than against responses provoked by direct muscle stimulation (M-twitches); the second, Asterosaponin B, displays an inverted activity sequence in the blockade potency sense (M-twitch > N-twitch). These observations have been interpreted in terms of surface polarity differences among the sugars comprising model glycosidic chains in the two toxin structures. Brief studies on interactions between cholinergic tissues and the echinoderm saponin Holothurin B from H. vagabunda and H. lubrica , and Holothurin A from Actinopyga agassizi , are also reported. With the latter toxin, protection experiments employing its desulfated derivative are especially revealing.

Toxic effects induced in neuromuscular tissues by work in hyperbaric helium/oxygen/carbon dioxide environments

Abstract The rat phrenic nerve-diaphragm (PN-D) preparation working in isometric mode in vitro has been subjected to hyperbaric stress in helium/oxygen/carbon dioxide environments, at total pressures ranging upward to 315 psia. Major manifestations of twitch response failure during 1–45 min of working time have been observed as a complex function of total pressure and the partial pressures of the 3 gaseous components. Additionally, the muscle undergoes dynamic changes in baseline tension under load during working exposure to these hyperbaric atmospheres, with considerable excursions in both a positive and negative sense, but experiences no loss in fibril ATPase content. Tissue viability in terms of prolonged retention of twitch response capability in hyperbaric He/O 2 /CO 2 atmospheres appears to require gaseous CO 2 at a partial pressure level of approximately 0.05 ata or greater, and involves some degree of interdependence of CO 2 and O 2 levels at each total pressure applied. In comparison of effects produced by ternary gas mixtures at equivalent total and partial pressures, it has been observed that He as a major component is more toxic than N 2 with respect to maintenance of working viability of PN-D preparations saturated with the respective gases. These findings have been discussed in the framework of possible tissue interactions with hyperbaric gases leading to alterations in baseline tension and decay of excitability.

Effects of pressure and muscle loading on the toxic actions of echinoderm saponins in neuromuscular tissues

Abstract The toxic marine saponin holothurin A from the Bahamian sea cucumber has been studied with regard to potency in blockade of responses of phrenic nerve-diaphragm (PN-D) preparations from the rat and the guinea pig under the additional stresses of high environmental pressure or variable loading of the muscle. In the rat tissue, the toxin (H − ) and its desulfated derivative (DeH) afford a contrast in sensitivity to the effects of elevated pressure: (a) the potency of H − at 1.0 × 10 −4 m is quite high at 14.7 psia, falls sharply as pressure is increased to 130 psia, and then increases moderately as pressure is further raised toward 330 psia; (b) the effect of increased pressure on DeH potency is only marginal. At ambient pressure, the effectiveness of 1.0 × 10 −4 m H − in depressing twitch responses of rat or guinea pig PN-D preparations is quite high near zero loading of the muscle, and falls to negligible levels as the static loading factor is increased toward 10–20 g/g of tissue. These observations are interpreted in terms of a working model for toxin receptors in junctional areas of PN-D tissues.

Interactions of the echinoderm toxin holothurin a and its desulfated derivative with the cat superior cervical ganglion preparation

Abstract Purified samples of the toxin Holothurin A (H−) elaborated by the sea cucumber Actinopyga agassizi, Selenka and of its neutral desulfated derivative (DeH) were studied for actions on the cat superior cervical ganglion preparation. It was observed that each saponin produces irreversible inactivation of the ganglion on injection into its bathing circulation, and that the charged anion H− is about one order of magnitude more potent in this regard than its neutral congener DeH. However, at levels (≤5 × 10−3 M) below its own effective blockade concentration, DeH is able to extend markedly the survival of ganglionic excita- bility against the rapid destruction normally wrought by 1 × 10−3 M injections of H−. Mechanisms for toxin-receptor interactions leading to H− destruction of excitability and to the partial protection afforded by DeH are briefly discussed.

Toxic effects of carbon dioxide and ternary nitrogen-oxygen-carbon dioxide hyperbaric atmospheres on the work function of cholinergic tissues

Abstract The excised phrenic nerve-diaphragm (PN-D) preparation from the rat, working in isometric mode under direct and indirect electrical stimuli, has been subjected to hyperbaric atmospheres of N2/O2/CO2 in a total pressure (pT) range of 15–215 psi and with CO2 content varying from 1 to 5 mole percent. Work function has been found to vary sensitively with pT and CO2 content of the gaseous environment, and with total working time of the encapsulated preparation. The tissue exhibits response behavior pointing to toxic actions of both high pressures and CO2 partial pressures (ppCO2): (a) the N-twitch (indirect) response exhibits a biphasic behavioral pattern of response augmentation-blockade as a function of pT and ppCO2, with blockade at low pressure levels, augmentation at intermediate pT values, and strong blockade at high pT-high CO2 levels; (b) M-twitch (direct) responses undergo progressive blockade as pT and ppCO2 levels are increased. Working intervals under stimulus in high pT-high CO2 gaseous environment produce losses in response amplitudes which increase sharply with working time, and which are accompanied by leaching of tissue constituents from the PN-D preparation. These results are discussed in terms of possible interactions of adducts from the ternary gas phase system with PN-D tissue receptors, leading to the observed changes and losses in tissue function.

Alterations in chemical blockade of cat gastrocnemius-soleus tissues under hyperbaric HeO2 atmospheres☆

Abstract The blockade responses of gastrocnemius-soleus (G-S) tissues to infusion with the quaternary ester tropine-p-tolylacetate methiodide (T) have been studied in vivo in the cat as a function of the composition and total pressure of the environmental breathing atmosphere. The G-S preparation itself is fully viable and capable of performing sustained isometric work under burst stimuli (40, 100 Hz) to the nerve for periods in excess of 2 hr, at tissue saturation with pressures ranging from 1 absolute atmospheric pressure (ata) ( N 2 O 2 ) to 266 psig ( He O 2 ). The standard blockade at 1 ata elicited by slow infusion of 1.0 × 10−2 m ester T amounts to extinction of response tension within 3–8 min. As the pressure is increased to 100 psig using He O 2 mixture, the degree of blockade induced by T at reference infusion times is sharply reduced, remains low at a total saturating pressure of 200 psig, and rises somewhat at 266 psig to modest levels that are still well below the blocking efficacy met at atmospheric pressure. Reasons for this striking dependency of blockade potency of a quaternary ester on external pressure are sought in terms of a deformable pore or crevasse model for receptor surfaces in striated muscle systems.

Changes in contractility of cat gastrocnemius tissues controlled by aryl ester infusion and stimulus burst frequency

Intravenous infusion of the quaternary aminoester tropine p-tolylacetate methiodide (I) or its tertiary desmethyl derivative (II) into the blood supply of the cat medial gastrocnemius preparation results in graded degrees of augmentation (20% maximum) and blockade of isometric muscle contraction, in response to electrical stimuli. The biphasic response perturbation pattern is dependent on ester infusion concentration, and in part on the frequency of pulses in the bursts of electrical stimuli delivered to the innervation trunk: (a) with ester I, burst frequencies in the 25–40 Hz region generate peak response augmentation with ester concentrations near 1 × 10−4 to 1 × 10−5 m; (b) at higher stimulus frequencies in the 65–100 Hz range, a second muscle response augmentation peak is uncovered at the 1 × 10−9 m infusion level of I; and (c) at approximately 5 × 10−3 m concentration of I in the infusate, a reference response blockade is attained which is nearly independent of stimulus frequency employed. Ester II in conjunction with 40 Hz stimulus frequency is weaker than I in evocation of response augmentation by about one order of magnitude in concentration requirement. These results on response alteration with the medial gastrocnemius preparation, in contrast with results of corresponding ester infusion experiments using the cat soleus tissues, are in accord with the concept that chemical events underlying muscle response perturbation involve a higher degree of neural control with the soleus than with the gastrocnemius neuromuscular tissues.

Ester and stimulus frequency mediated perturbations of response patterns from cat soleus tissues

Abstract Contractile response patterns evoked by the tertiary aminoester tropine p -tolylacetate (II) and its quaternary methiodide (I), on steady-state infusion into the in situ cat soleus neuromuscular preparation, have been studied as a function of ester concentration and frequency of electrical stimuli to nerve. With spaced bursts of stimuli to nerve producing isometric response bursts from muscle, intraarterial administration of either ester results in a biphasic action pattern; at low ester concentrations small degrees (5–10%) of response amplification are met, with a progressive transition to response blockade at higher ester levels. For the quaternary ester I, the effects of individual variation in concentration of agent and mean frequency of stimulus mode employed appear to be inversely related in production of response amplification from soleus muscle, with pairing of high concentration-low frequency or conversely low concentration-high frequency parameters leading, respectively, to optimum amplification. These results are discussed in terms of possible mechanisms governing chemical effects mediated at the soleus neuromuscular junction.

Aryl ester infusion and evoked responses from the soleus-gastrocnemius tissue complex in the cat.

The in vivo soleus-gastrocnemius neuromuscular preparation in the cat, working in isometric mode under burst electrical stimuli to the nerve trunk, has been perfused at constant rate with variable concentrations of the quaternary ester tropine-p-tolylacetate methiodide (I). Elements of response augmentation and blockade as a function of ester I infusate concentration and neural stimulus frequency have been observed. The augmentation phase of response perturbation is of brief duration, with optimum responses at low stimulus frequencies (25–40 Hz pulses) and infusate I concentrations near 1 × 10−6 and 1 to 5 × 10−3m, while response blockade is nearly independent of stimulus frequency and becomes prominent at I levels of 5 × 10−3m and greater. On comparison of these ester I-frequency induced perturbations of fused soleus-gastrocnemius muscle responses with those previously noted for the separate in vivo soleus and gastrocnemius preparations, it appears that the fused muscle complex is most nearly related to the gastrocnemius in its response properties.

Blockade of superior cervical ganglionic transmission by tropine-p-tolylacetate and its quaternary methiodide derivative

Abstract The in vivo cat superior cervical ganglion (G) preparation was used in a study of ganglionic blockade evoked by the tertiary ester tropine- p -tolylacetate(II) and its quaternary methiodide derivative (I), singly and in mixtures. It was observed that the individual potency indexes for induction of blockade fell in the strength sequence I > II, that sensitivity of the ganglionic tissues to blockade by these esters was less than that of phrenic nerve-diaphragm tissues, and that quaternary I and tertiary II engaged in a strong antagonism at ganglionic receptors. The extent of the antagonism increased with total concentration level of ester mixtures reaching the ganglion and was fairly independent of the I:II ratio at any given total concentration of injected ester mixture. The antagonism phenomenon was examined in terms of possible mechanisms underlying the reversible blocking interactions of the two esters with G tissue receptor systems.