A. Salleo

Viscosity and density of lysozyme in water

Abstract The viscosity and density of solutions of lysozyme in water have been measured in the range of concentration from 0.2% to 26% by weight. It is found that a critical concentration exists, namely 17% by weight, which separates two distinct kinds of behaviour. The results agree with those previously obtained by other authors using Raman spectroscopy, and are also compared with results obtained from some electrolytic solutions.

Diffusion Coefficient of Lysozyme in Water

The diffusion coefficient in aqueous solution of lysozyme has been measured by means of the optical beating spectroscopy, at different concentrations and scattering angles. It has been found that the decay of the fluctuation of the concentration cannot be represented by a single exponential law. There is a long tail associated with some slow decaying quantity. In addition, both the short- and the long-time behaviour turns out to be angle and concentration dependent, indicating the existence of some sort of structure. The commonly accepted literature value for the diffusion coefficient is recovered only in the limit of large scattering vectors. The above-mentioned results are also discussed in the frame of other experimental results obtained for the same system.

Hyposmotic shock-induced discharge in acontia ofCalliactis parasitica is blocked by gadolinium

On acontia ofCalliactis parasitica it was observed that mechanical stimuli applied by a gelatin probe, a method effective in tentacles of Anthozoa, do not induce the discharge of nematocytes. Hyposmotic shock, performed by treatment with NaCl solution 35% hyposmotic with respect to sea water, induces, in the presence of Ca2+, the discharge that spreads along the acontial filament, as previously observed following treatment with SCN−. The hyposmotic shock-induced discharge is blocked by Gd3+ at a concentration of 1 μM. 10 μM Gd3+ prevents also the SCN−-induced discharge. These results suggest the presence of stretch activated cation channels either in nematocytes and/or in supporting cells as well as a possible effect of SCN− on this class of ion channels.

Discharge characteristics of nematocysts isolated from acontia ofCalliactis parasitica

Experiments were performed on specimens ofCalliactis parasitica collected near Plymouth in April 1987 and in the Mediterranean between September 1987 and April 1988. Undischarged nematocysts (basitrichous isorhizas) were separated from the acontia of by using 1M glycerol, 1M citrate, 0.5% Nonidet or 0.5% Triton X-100 as isolating agents, or by freezing the acontial tissue. The mechanisms of extrusion were not studied. The effectiveness of 50 mM thioglycolate in discharging nematocysts isolated by the above methods and suspended in Ca- and Mg-free artificial sea water (ASW) was investigated. Nematocysts extruded in glycerol were more responsive to thioglycolate than those extruded in citrate. Capsules isolated in non-ionic detergents, however, and those obtained by freezing were not discharged by thioglycolate. If capsules extruded in glycerol were suspended in ASW and this was replaced with distilled water, they did not respond to thioglycolate. The effect of distilled water was only partly reversible. It was observed that these nematocysts, unlike those ofPelagia noctiluca andAiptasia mutabilis previously investigated, did not release measurable amounts of free Ca2+ during discharge. It is suggested that if calcium is not involved in the mechanism of discharge of isolatedC. parasitica nematocysts then some other ionic species may stabilize the resting condition of these capsules.

Spread of experimentally induced discharge of the nematocytes in acontia of Calliactis parasitica

Abstract 1. 1. In acontia of Calliactis parasitica 100–553 mM SCN − induces the sequential spreading of discharge of nematocytes. K + at the same concentrations causes the contemporaneous mass discharge of the entire cell population, while at 50–85 mM concentrations induces a spreading discharge. Both responses are Ca 2+ dependent. 2. 2. The same triphasic signal is associated with both SCN − and K + -induced discharge. 3. 3. I-Octanol prevents the discharging effects of either SCN − and K + . 4. 4. It is suggested that an inflow of Ca 2+ triggers the discharge and that intercellular junctions may couple the supporting cells and the nematocytes.

Generazione di potenziali elettrici durante scorrimento di fluidi nello xilema. (Nota preliminare)

Abstract Generation of electric potentials during flow of fluids in the xylem vessels (Preliminary Report).—The streaming potential generated by the flow of fluids in the xylem vessels has been studied on segments of stem of Cucurbita sechium edule recently excised. The streaming potentials encountered in such experiments exhibit a much longer time constant than those observable in glass capillaries. The streaming potential so generated induces a superimposed rapid electric activity consisting of spikes. Finally, a peculiar relationship between the streaming potential and applied Δp has been encountered. Some tentative explanations of such results are suggested.