At least two people are known to have died as a direct result of Blue-ringed Octopus bites, and other near fatalities have been recorded. Both species of Blue-ringed Octopus, Hapalochlaena lunulata (Quoy and Gaimard) and H. maculosa Hoyle, have-been responsible for human fatalities. This study of Hapalochlaena deals primarily with the structure and function of the venom apparatus, the method of secretion and composition of the venom, and the effects and mode of operation of the venom on pharmacological preparations.
The diagnosis of the genus and species and the general morphology are discussed. It is shown that while most morphological measurements and indices show range overlap, there is significant difference between some indices of body, arm and web proportion between the two species. A brief account is provided of what little is known of the life history of Hapalochlaena.
Histological and histochemical studies of the venom apparatus were conducted. The venom is elaborated in two cell types within the posterior salivary glands. Basophilic cells produce granules which contain muco- protein. Acidophilic cells produce granules which are admixtures or conjugates of carbohydrate, protein and lipid substances. The fine structure of the glandular epithelium was examined and the elaboration and secretion of the products of the secretory cells are discussed. It is suggested that the continuous activity of the gland, coupled with an asynchronous, holocrine mode of secretion is efficient for opportunistic feeding and defence. Nervous control of envenomation is discussed.
Significant amounts of tyrosine and tryptophan are shown to be present in the acidophilic secretory cells. 5-hydroxytryptamine is synthesised and stored in acidophilic cells, which exhibit the properties of entero- chromaffin cells. The role of 5-hydroxytryptamine in the venom is discussed. As well as its known effect on prey organisms, it may play a role in the control of venom extrusion within the ducts of the venom apparatus.
The effects of the venom on human victims have been recorded. Allergic and toxic reactions can be identified. Loss of muscular coordination followed by paralysis of voluntary muscle is typical and, in fatal cases, leads to respiratory and subsequent heart failure. Pharmacological studies confirm that the venom acts principally on nerves and voluntary muscle; any cardiac effects being secondary. Neurotoxic activity and direct inhibitory activity on skeletal muscle contractions elicited in response to electrical stimulation are described. There is some activity on smooth muscle, but this may be explained by the presence of unidentified amines in the venom rather than by a toxic fraction.
Nine low molecular weight fractions were isolated from the venom by thin-layer chromatography. Two of these fractions were pharmacologically active. One possessed neurotoxic activity, blocking conduction of impulses in nerves. The other proved lethal to mice and mimicked the activity of venom on pharmacological preparations. The lethal fraction is a polar molecule with hydrophilic and lipophilic properties, and its activities resemble those of maculotoxin, isolated by Croft and Howden (1972). The chemical nature of this fraction is discussed briefly.
The activity of the lethal fraction on isolated pharmacological preparations is compared with that reported for maculotoxin (Dulhunty and Gage, 1971). It is shown that activity of the venom may upset the movement of calcium ions across membranes. Experiments, especially with barnacle muscle preparations, suggest that this is achieved by upsetting the interdependent movements of sodium and calcium ions at cell membranes. The venom apparently does not complex calcium.
The lethal fraction of the venom of Hapalochlaena may prove useful in experiments conducted to ascertain the mode of action of sodium ions at cell membranes and their influences on the movements of associated ions.