Blood volume of the ascidian Pyura praeputialis

Blood dilution curves have been obtained by injecting ¹²⁵I labelled albumin and ¹²⁵I labelled gamma-globulin into the blood of Pyura praeputialis . After mixing is complete the dilution curve shows a two-stepped pattern.
There is some question as to how the two steps of the curve should be interpreted. The first step has been extrapolated to give blood volume s.s. , i.e. volume of the vessels, sinuses and lacunae of the vascular system. Values for this range from 30% to 45 % of body weight, with a mean value of 35%.
The second step has been extrapolated to give total extracellular fluid volume, i.e. blood volume plus interstitial fluid volume. Values for this range from 21 % to 52 % of body weight, the average being 38 %.
The interstitial space ranges from 15 % to 32 % of the weight of the visceral mass, the average being 23 %.
The rationale for the above interpretation of the dilution curve is stated and discussed. Most reliable is extracellular fluid volume which probably corresponds to the blood volume of other invertebrates with open systems.
An attempt was made to assess the relative importance of (a) the visceral circuit and (b) the tunic circuit, by comparing the specific activities of the visceral mass and the tunic. The specific activities indicate little or no blood in the tunic circuit: this result is suspect.     

Vascular physiology of the ascidian Pyura praeputialis

Blood pressure was measured at both ends of the heart of Pyura praeputialis (Heller) after removing the tunic.
For posterior anterior heart waves average upstream pressures were 23–25 mm H₂O (positive): corresponding downstream pressures averaged 8 mm H₂O (negative). For anterior posterior waves average upstream pressures were 17–18 mm H₂O (+) and downstream values were 7–8 mm H₂O (-). Maximum pulse amplitudes recorded were about 30 mm H₂O (upstream).
Speed of the peristaltic wave was 25-31 mm/s. In one experiment the speed was demonstrably different over the two halves of the heart (48 mm/s over the rear half and 29 mm/s over the front half).
Number of peristaltic waves per series (i.e. between successive reversals) varied from 20 to 178. Duration of each series varied from 120 s to 690 s. Wave frequency ranged from 8 to 21 per min. Reversal frequency ranged from 5 to 30 reversals per hour.
Most preparations showed periods of reduced heart activity (rest periods) during the the 2 4 h of the experiment. All showed spasmodic contractions of the mantle muscles which caused pressure surges in the vascular system.
It is shown that, in both directions of beat, most or all of the pressure wave is contributed by the front half of the heart (half towards which peristaltic wave is travelling). This can be related to the reversed spiral structure of the heart: each half of the heart (i.e. each spiral) serves primarily as the pump for one direction.     

Foraging behavior of the American oystercatcher Haematopus palliatus pitanay (Murphy 1925) on the intertidal ascidian Pyura praeputialis (Heller 1878) in the Bay of Antofagasta, Chile

Oystercatcher foraging behavior has been described for diverse intertidal prey such as limpets, mussels, and oysters. This paper describes foraging behavior of the American oystercatcher, Haematopous palliatus pitanay, on attached and wave-dislodged ascidians, Pyura praeputialis (prey with a restricted geographic range of 70 km) in the Bay of Antofagasta, Chile. Stabbed holes on the top of the ascidian's tunic, probing excursions, handling time, and five prey-handling sequential stages (striking, hammering, prying, cavity food searching, and swallowing) are described and measured. The need to determine ascidian profit-ability for oystercatcher species in Australia and Chile is highlighted. Received: January 19, 2000 / Accepted: July 23, 2000     

Passive flow through an unstalked intertidal ascidian: orientation and morphology enhance suspension feeding in Pyura stolonifera

Passive flow is believed to increase the gains and reduce the costs of active suspension feeding. We used a mixture of field and laboratory experiments to evaluate whether the unstalked intertidal ascidian Pyura stolonifera exploits passive flow. We predicted that its orientation to prevailing currents and the arrangement of its siphons would induce passive flow due to dynamic pressure at the inhalant siphon, as well as by the Bernoulli effect or viscous entrainment associated with different fluid velocities at each siphon, or by both mechanisms. The orientation of P. stolonifera at several locations along the Sydney-Illawarra coast (Australia) covering a wide range of wave exposures was nonrandom and revealed that the ascidians were consistently oriented with their inhalant siphons directed into the waves or backwash. Flume experiments using wax models demonstrated that the arrangement of the siphons could induce passive flow and that passive flow was greatest when the inhalant siphon was oriented into the flow. Field experiments using transplanted animals confirmed that such an orientation resulted in ascidians gaining food at greater rates, as measured by fecal production, than when oriented perpendicular to the wave direction. We conclude that P. stolonifera enhances suspension feeding by inducing passive flow and is, therefore, a facultatively active suspension feeder. Furthermore, we argue that it is likely that many other active suspension feeders utilize passive flow and, therefore, measurements of their clearance rates should be made under appropriate conditions of flow to gain ecologically relevant results.     

Interactions between exogenous and endogenous retroviruses

Retroviruses are distinguished from other viruses by several features. Notably, some retroviruses are present as normal elements in the genomes of virtually all vertebrates (endogenous proviruses). Others are exogenous, i.e. horizontally transmitted agents, many of which cause fatal diseases. The endogenous retroviruses are genetically transmitted and to a large extent their significance is uncertain. However, there is evidence suggesting that they contribute to the development of diseases in several animal species. Most importantly, some endogenous retroviruses are capable of interacting with exogenous counterparts through a variety of different mechanisms with serious consequences to the host. Conversely, others are advantageous in that they protect against exogenous retroviruses. In this review various types of interactions between endogenous and exogenous retroviruses are discussed, including receptor interference, recombination, phenotypic mixing, immunological interactions and heterologoustrans-activation.     

Troponin and its components from ascidian smooth muscle

Troponin was isolated from the thin filaments of ascidian smooth muscle and separated into three components by ion-exchange chromatography, the molecular weights of which were 33,000, 24,000, and 18,000, respectively. The three components were designated as troponin t (TN-T), troponin I (TN-I), and troponin C (TN-C) in order of molecular weight, since each component had properties similar to those of the respective components of vertebrate skeletal-muscle troponin. The ascidian troponin or the mixture of the three components conferred Ca2+-sensitivity on reconstituted rabbit actomyosin in the presence of tropomyosin. One of the characteristics of the ascidian troponin was Ca2+-dependent activation of actin-myosin interaction in collaboration with tropomyosin, whereas its inhibitory action on the actomyosin ATPase in the absence of Ca2+ was less remarkable. From this, it is concluded that in the ascidian smooth muscle actin-myosin interaction is regulated by an actin-linked troponin-tropomyosin system, but the ascidian troponin acts as a Ca2+-dependent activator of an actomyosin system.     

Interactions between human endogenous and exogenous retroviruses

Retrovirus genes have become inserted into the human genome for more than one million years. These retroviruses are now inactivated due to mutation, such as deletions or nonsense mutations. After mutation, retroviruses eventually become fixed in the genome in the endogenous form and exist as traces of ancient viruses. These retroviruses are called human endogenous retroviruses (HERVs). HERVs cannot make fully active viruses, but a number of viral proteins (or even virus particles) are expressed under various conditions. By comparison with ERVs, some exogenous retroviruses are still infectious and cause serious diseases threatening human life. Recent studies have shown that some elements of HERVs are closely related to other exogenous retroviruses, including human immunodeficiency virus (HIV). This review will describe the regulation and interaction between HERVs and other active viral infections. In addition, we introduce the development of vaccines and therapeutic agents against these viral infections through the use of HERV elements.     

Ethanolaminephosphotransferase in rat lung: selectivity for endogenous and exogenous diacylglycerol

Ethanolaminephosphotransferase (EC 2.7.8.1) activity was determined in lung microsomes using diacylglycerols generated endogenously from [14C]glycerol 3-phosphate and different mixtures of fatty acids. Ethanolaminephosphotransferase used endogenously generated dipalmitoylglycerol better than dioleoylglycerol. The apparent Km and the reaction rates for four different endogenously generated mixtures were the same (16 nmol/mg microsomal proteins). The apparent Km values for CDP-ethanolamine were the same (0.26 mm) for endogenously generated dipalmitoylglycerol and dioleoylglycerol. The amount of diacylglycerol generated in microsomes was 2-3-times the apparent Km for diacylglycerol. Dipalmitoylglycerol, supplied exogenously as a Tween 20/phosphatidylglycerol emulsion, was nearly twice as active as dioleoylglycerol. Both dipalmitoylglycerol and dioleoylglycerol were more active as substrates when emulsions were made with phosphatidylglycerol/Tween 20 than with Tween 20 alone. The results suggest that ethanolaminephosphotransferase in lung is relatively nonselective for molecular species of diacylglycerol. In addition, the results suggest that the concentration of diacylglycerol and the physical state in which it is presented to the enzyme can affect the apparent selectivity of ethanolaminephosphotransferase for diacylglycerols.