The Discharge of Nematocysts in Relation to Properties of the Capsule

Robson, E. A.

doi:10.5134/175752

Cited by 23 publications

(17 citation statements)

References 18 publications

(15 reference statements)

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“…The rest of the overall volume will be taken up by the volume of the capsule wall and the inverted tubule. Robson (1973) estimated the volume of the inverted tubule to be in excess of 50% of the overall capsule volume, which agrees with the present results. The relatively small volume of venom elaborated from p-mastigophores (3%) is probably due to the relatively large volume occupied by the shaft region of the tubule in this type of nematocyst.…”

Section: Discussionsupporting

confidence: 92%

Cnida discharge and the mechanism of venom delivery in Anemonia viridis (Cnidaria, Actiniaria)

Thomason

1991

Hydrobiologia

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Cnida discharge in the actinian Anemonia starts with the extrusion of the capsule from the cnidocyte followed by the eversion of the tubule. As the tubule everts, it maintains a tightly closed tip until fully everted. This is considered to be essential for a capsule to discharge as a result of an increase in intracapsular pressure. Venom volumes were measured in 3 types of nematocyst: 408 pm 3 , 98 pm 3 , and 9 pm 3 . Venom flow rates were estimated to range from >43 to 324 tm 3 s -. It is suggested that the' intracapsular pressures required for these flow rates range from 9.7 x 105 to 1.9 x 106 Pa.

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Section: Discussionsupporting

confidence: 92%

Cnida discharge and the mechanism of venom delivery in Anemonia viridis (Cnidaria, Actiniaria)

Thomason

1991

Hydrobiologia

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“…Although the structural events during eversion of the thread have been described in detail (1), little is known about the mechanism of discharge (2)(3)(4)(5). Recently, Lubbock and Amos (6) found that discharge could be initiated in vitro by the removal of bound calcium from the fluid inside the nematocyst; calcium removal increased the osmotic pressure of the nematocyst fluid, thus producing an influx of water from the external medium and an increase in the internal hydrostatic pressure of the capsule.…”

mentioning

confidence: 99%

Novel role of calcium in exocytosis: mechanism of nematocyst discharge as shown by x-ray microanalysis.

Lubbock¹,

Gupta²,

Hall³

1981

Proc. Natl. Acad. Sci. U.S.A.

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Mature nematocysts of the sea anemones Rhodactis rhodostoma and Anthopleura elegantissima contain a fluid that has a high concentration of solutes and is extraordinarily rich in calcium (ca. 500-0 mmol/kg wet weight); this contrasts with the surrounding cytoplasm which is rich in potassium but poor in calcium. The undischarged capsule is surrounded by a membrane that probably acts as a selective permeability barrier between the cytoplasm and the nematocyst fluid. During discharge the nematocyst moves to the surface of the nematocyte and comes into contact with the external sea water medium. Calcium, which may be bound to proteins in the undischarged state, is rapidly lost from the fluid; at the same time, sea water enters the capsule. In vitro experiments have already shown that calcium loss increases the osmotic pressure of the capsular fluid, causing an influx of water from the external medium; this influx appears to increase the hydrostatic pressure inside the capsule to the point that the thread everts explosively.Nematocysts are stinging organelles found in cnidarians; each one consists ofa closed capsule which contains an inverted harpoon-like thread that can be discharged explosively. Although the structural events during eversion of the thread have been described in detail (1), little is known about the mechanism of discharge (2-5). Recently, Lubbock and Amos (6) found that discharge could be initiated in vitro by the removal of bound calcium from the fluid inside the nematocyst; calcium removal increased the osmotic pressure of the nematocyst fluid, thus producing an influx of water from the external medium and an increase in the internal hydrostatic pressure of the capsule. It was notable that alterations in the permeability of the capsule wall to water did not seem to be involved in controlling discharge in vitro. At that time, the relevance of the in vitro experiments to nematocyst discharge in vivo was not clearly established because data were not available on the ionic changes occurring under natural conditions.In the present study, we examined, by x-ray microanalysis of frozen sections, the elemental composition of both excited and unexcited nematocytes in the sea anemones Rhodactis rhodostoma and Anthopleura elegantissima. Our results enable us to present a generalized model of the events that take place during excitation. MATERIALS AND METHODSMesenterial filaments from R. rhodostoma were placed in synthetic seawater (Tropic Marin Neu; specific gravity, 1.021) containing 16.8% (wt/wt) dextran (250,000 daltors; Sigma, clinical grade). To quench freeze, filaments with droplets of dextran/ sea water were placed on the truncated conical tips of copper pins and rapidly immersed in a well-stirred slush of (monochlorodifluoromethane, m.p. -181'C) (7-9). In certain cases, filaments mounted on copper pins were electrically stimulated <3 sec before instant quenching in order to induce nematocyst discharge. Acrorhagial tissue was obtained from A. elegantissima by removing inflated acrorhagi with ...

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“…For further examples of recent contributions in this field, see MATTERN, PARK, and DANIEL (1965), WESTFALL (1965), andSLAUTTERBACK (1967). In the present symposium also, good many interesting pictures have been presented by RoBSON (1973). Such a situation is apt to divert the imaginative mind of observers in various ways, as it was just the case in past in the golden age of light microscope.…”

Section: Determinism and Mechanism Of Dischargementioning

confidence: 94%

The "Cnidoblast" as an Excitable System

Yanagita¹

1973

Publ. SMBL

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It seems established by now that nettling response as it is given normally by cnidarian nematocysts belongs to a rather standard type of physiological excitation event, though there is still some question about the functional significance of the morphological "cnidoblasts". It is instructive to consider this subject in comparison with that of muscle contraction response provided that one adopts the view of "post-energization' rather than that of "pre-energization". One of the centers of interest is at present in identification of coupler agent that mediates between the external excitation event and internal explosion event. For this problem, the experimentation with isolated nematocysts are of critical role. It was shown that apparently inconsistent situations are to be found even among the same type of cnida from closely related species, and it is interesting to see how one can negotiate such diversions to bring them into fundamental uniformity. Efforts so far made revealed us that there is still need for studying somewhat intricated interrelationship between, water, anions, and cations as to triggering of the isolated cnidae. Such study may lead to an understanding of the mode of operation of cnidae in situ in the normal response system. The discussion extends further to include the problem of remote control of nematocyst discharge.

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The Discharge of Nematocysts in Relation to Properties of the Capsule

Cited by 23 publications

References 18 publications

Cnida discharge and the mechanism of venom delivery in Anemonia viridis (Cnidaria, Actiniaria)

Cnida discharge and the mechanism of venom delivery in Anemonia viridis (Cnidaria, Actiniaria)

Novel role of calcium in exocytosis: mechanism of nematocyst discharge as shown by x-ray microanalysis.

The "Cnidoblast" as an Excitable System

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