The ionic basis of the resting potential of molluscan unstriated muscle

Summary The membrane potential (Vm) of unstriated, non-spiking fibres from the buccal retractor muscle of the opisthobranch molluscPhiline aperta is primarily determined by the distribution of the potassium ion across the membrane. In salines where potassium is varied and chloride remains constant or nearly so, the membrane potential varied with log external K⁺ with a slope of 50.6 (±2.3) mV per decade. In chloride-free salines the slope was 48.5 mV per decade. The experiments were conducted at temperatures of 18–20° C.A ten-fold reduction in external chloride concentration depolarised the fibres by around 10 mV, indicating that chloride permeability makes some contribution to Vm. In salines where [K]₀·[Cl]₀ is constant the Nernst slope was 55.8 mV per decade compared with the theoretical value of 58 mV.The experimental data suggest that the internal potassium concentration of the fibres is 247±31 mM and pNa/pK is 0.01, giving a predicted value of Vm in sea water of –72 mV. The membrane potential of 90 fibres measured in sea water was –74.2±1.3 mV. The membrane contains an electrogenic sodium pump which contributes 4–5 mV to the membrane potential.     

广东上川岛潮间带软体动物的分布

对上川岛潮间带软体动物进行了采集调查,共鉴定软体动物172种,分属53科。其中瓣鳃纲20科81种,占总数47．09％,腹足纲33科91种,占总数52．91％。分析表明,其区系特点是以南海亚热带-热带种和东海、南海亚热带种为主要成分。     

Biosynthesis of an acidic galactan and sulfated glycosaminoglycans during embryonic development of the mollusc Pomacea sp.

The synthesis of acidic polysaccharides by eggs of Pomacea sp. at different stages of development was studied. By day 3 after oviposition an acidic galactan became apparent. This compound reaches its maximum concentration by day 6 and then slowly decreases in concentration, no longer being detectable by day 12. Among the sulfated glycosaminoglycans, chondroitin sulfate is the first to appear (day 10), followed by heparan sulfate and other sulfate glycosaminoglycans, which were synthesized in large amounts until hatching (around day 15). Each one of the compounds was purified and characterized by chemical analysis and enzymatic degradation. The synthesis and characterization of the sulfated glycosaminoglycans was confirmed by the use of radioactive sulfate applied to intact eggs at different stages of development. These studies suggest that the main difference between vertebrate and mollusc development regarding the acidic polysaccharides is that hyaluronic acid seems to be absent during early mollusc development. It is proposed that the acidic galactan may be synthesized from the neutral galactan, already present in the eggs in high amounts, and may replace this glycosaminoglycan in the mollusc embryogenesis.     

Freezing in the Antarctic limpet, Nacella concinna

The process of organismal freezing in the Antarctic limpet, Nacella concinna, is complicated by molluscan biology. Internal ice formation is, in particular, mediated by two factors: (a) the provision of an inoculative target for ice formation in the exposed mucus-secreting foot; and (b) osmoconformity to the marine environment. With regard to the first, direct observations of the independent freezing of pedal mucus support the hypothesis that internal ice formation is delayed by the mucal film. As to the second, ice nucleation parametrics of organismal tissue (head, midgut, gonad, foot) and mucus in both inter- and subtidal populations were characterized by high melting points (range = −4.61 to −6.29 °C), with only c.50% of a given sample osmotically active. At this stage it would be premature to ascribe a cryo-adaptive function to the mucus as the protective effects are more readily attributed to the physical properties of the secretion (i.e. viscosity) and their corresponding effects on the rate of heat transfer. As it is difficult to thermally distinguish between the freezing of mucus and the rest of the animal, the question as to whether it is tolerant of internal as well as external ice formation remains problematic, although it may be well suited to the osmotic stresses of organismal freezing.     

On fixed precision level sequential sampling

Summary It is proposed that the sequential sampling design ofKuno (1969) for estimating populations with a fixed level of precision be modified by using σ²=am ^b for the variance-mean relationship for most field distributions of organisms. This function yields a straight line “stop line” rather than a curve. An example is calculated and used with field data.     

Evolution and biomineralization of pteropod shells

Shelled pteropods, known as sea butterflies, are a group of small gastropods that spend their entire lives swimming and drifting in the open ocean. They build thin shells of aragonite, a metastable polymorph of calcium carbonate. Pteropod shells have been shown to experience dissolution and reduced thickness with a decrease in pH and therefore represent valuable bioindicators to monitor the impacts of ocean acidification. Over the past decades, several studies have highlighted the striking diversity of shell microstructures in pteropods, with exceptional mechanical properties, but their evolution and future in acidified waters remains uncertain. Here, we revisit the body-of-work on pteropod biomineralization, focusing on shell microstructures and their evolution. The evolutionary history of pteropods was recently resolved, and thus it is timely to examine their shell microstructures in such context. We analyse new images of shells from fossils and recent species providing a comprehensive overview of their structural diversity. Pteropod shells are made of the crossed lamellar and prismatic microstructures common in molluscs, but also of curved nanofibers which are proposed to form a helical three-dimensional structure. Our analyses suggest that the curved fibres emerged before the split between coiled and uncoiled pteropods and that they form incomplete to multiple helical turns. The curved fibres are seen as an important trait in the adaptation to a planktonic lifestyle, giving maximum strength and flexibility to the pteropod thin and lightweight shells. Finally, we also elucidate on the candidate biomineralization genes underpinning the shell diversity in these important indicators of ocean health.     

The Effects of Lithium on a Neuronal in Vitro Orcadian Pacemaker

Previous studies have suggested a causal connection between abnormalities of the circadian system and affective disorders. The effectiveness of lithium or rubidium as a treatment for affective disorders and the ability of lithium or rubidium to influence circadian pacemakers has stimulated research into the mechanism of lithium's action on circadian systems. In this study we used a neuronal in vitro circadian pacemaker preparation, the eye of the mollusc Bulla, to examine the cellular effects of lithium and rubidium. Continuous extracellular LiCl application lengthens the period of the circadian rhythm of the Bulla pacemaker in a concentration-dependent manner. Rubidium was found to be more effective than lithium in period lengthening. Stable phase delays were generated by 2-h pulses of 395 mM LiCl applied extracellularly from zeitgeber time (ZT) 5-7 (mid subjective day). Concomitant continuous application of 16 mM LiCl and light (a depolarizing agent) generated period lengthening substantially greater than the arithmetic sum of the modest period lengthening of each treatment alone. Furthermore, LiCl pulses, applied together with depolarizing extracellular KC1 concentrations, yielded an increasing magnitude of phase delays with increasing KC1 concentration. These data suggest that LiCl acts intracellularly on the circadian pacemaker cells by entering through a voltage-dependent channel, most likely a sodium channel.     

Functional neuroanatomy of the rhinophore of <Emphasis Type="Italic">Archidoris pseudoargus</Emphasis>

For sea slugs, chemosensory information represents an important sensory modality, because optical and acoustical information are limited. In the present study, we focussed on the neuroanatomy of the rhinophores and processing of olfactory stimuli in the rhinophore ganglion of Archidoris pseudoargus, belonging to the order of Nudibranchia in the subclass of Opisthobranchia. Histological techniques, fluorescent markers, and immunohistochemistry were used to analyse neuroanatomical features of the rhinophore. A large ganglion and a prominent central lymphatic channel are surrounded by longitudinal muscles. Many serotonin-immunoreactive (IR) processes were found around the centre and between the ganglion and the highly folded lobes of the rhinophore, but serotonin-IR cell bodies were absent inside the rhinophore. In contrast to the conditions recently found in Aplysia punctata, we found no evidence for the presence of olfactory glomeruli within the rhinophore. Using calcium-imaging techniques with Fura II as a calcium indicator, we found differential calcium responses in various regions within the ganglion to stimulation of the rhinophore with different amino acids. The lack of glomeruli in the rhinophores induces functional questions about processing of chemical information in the rhinophore.