Assessment of the pressure-volume relationship of the single ventricle of the grass shrimp, Palaemonetes pugio.

The ventricular pressure-volume (PV) relationship has been used extensively to study the mechanics and energetics in multi-chambered hearts of closed circulatory system vertebrates. In the current study we applied the use of PV loops in the assessment of cardiac mechanics and energetics in the single ventricle of a decapod crustacean possessing an open circulatory system. Anatomical differences between multi-and single-chambered hearts include multiple ostia entering and valved multiple arterial systems exiting the ventricle, and the neurogenic origin of the heartbeat in decapod crustaceans. However, the microscopic architecture and excitation-contraction coupling events are similar in both systems. Ventricular pressure and area were obtained independently and integrated into pressure-area loops. Area was then converted to volume to generate PV loops. Based on the PV loops generated in this study, the ventricle of Palaemonetes pugio processes the same primary phases of the cardiac cycle as ventricles from the multi-chambered hearts of vertebrates: (1) isovolumic contraction, (2) ventricular emptying, (3) isovolumic relaxation and (4) ventricular filling. The area enclosed by the PV loop provides a measure of stroke work and when multiplied by heart rate provides an assessment of cardiac work. This initial examination of PV loops from a single-ventricle decapod crustacean demonstrates the utility of this technique to further elucidate the cardiac mechanics and energetics of this system, and in particular during times of physiological stress.

Metabolic, respiratory and cardiovascular responses to acute and chronic hypoxic exposure in tadpole shrimp Triops longicaudatus.

Hypoxic exposure experienced during sensitive developmental periods can shape adult physiological capabilities and define regulatory limits. Tadpole shrimp were reared under normoxic (19-21 kPa O(2)), moderate (10-13 kPa O(2)) or severe (1-3 kPa O(2)) hypoxic conditions to investigate the influence of developmental oxygen partial pressure (P(O(2))) on adult metabolic, respiratory and cardiovascular physiology. Developmental P(O(2)) had no effect on metabolic rate or metabolic response to hypoxic exposure in adults. All rearing groups decreased O(2) consumption as water P(O(2)) decreased. Heart rate, stroke volume and cardiac output were independent of P(O(2)) down to 5 kPa O(2) in all rearing groups. Below this, cardiac output was maintained only in tadpole shrimp reared under severe hypoxic conditions. The enhanced ability to maintain cardiac output was attributed to an increase in hemoglobin concentration and O(2)-binding affinity in those animals. Oxygen-delivery potential was also significantly higher in the group reared under severe hypoxic conditions (1,336 microl O(2) min(-1)) when compared with the group reared under normoxic conditions (274 microl O(2) min(-1)). Differences among the rearing groups that were dependent on hemoglobin were not considered developmental effects because hemoglobin concentration could be increased within seven days of hypoxic exposure independent of developmental P(O(2)). Hypoxia-induced hemoglobin synthesis may be a compensatory mechanism that allows tadpole shrimp to regulate O(2) uptake and transport in euryoxic (O(2) variable) environments. The results of this study indicate that increased hemoglobin concentration, increased O(2)-binding affinity and transient decreases in metabolic demand may account for tadpole shrimp hypoxic tolerance.

Cardiac development in crayfish: ontogeny of cardiac physiology and aerobic metabolism in the red swamp crayfish Procambarus clarkii.

The cardiovascular system performs key physiological functions even as it develops and grows. The ontogeny of cardiac physiology was studied throughout embryonic and larval development in the red swamp crayfish Procambarus clarkii using videomicroscopic dimensional analysis. The heart begins to contract by day 13 of development (at 25 degrees C, 20 kPa O2). Prior to eclosion, heart rate (fH) decreases significantly. Previous data suggests that the decrease in cardiac parameters prior to hatching may be due to an oxygen limitation of the embryo. Throughout development, metabolizing mass and embryonic oxygen consumption primarily increased while egg surface area remains constant. The limited area for gas exchange of the egg membrane, in combination with the increasing oxygen demand of the embryo could result in an inadequate diffusive supply of oxygen to developing tissues. To determine if the decrease in cardiac function was the result of an internal hypoxia experienced during late embryonic development, early and late stage embryos were exposed to hyperoxic water (PO2 = 40 kPa O2). The fH in late stage embryos increased significantly over control values when exposed to hyperoxic water suggesting that the suppression in cardiac function observed in late stage embryos is likely due to a limited oxygen supply.

Environmental hypoxia influences hemoglobin subunit composition in the branchiopod crustacean Triops longicaudatus.

Hemoglobin (Hb) is a highly conserved protein that provides a vital link between environmental oxygen and its use and/or storage within an organism. While ubiquitous among vertebrates, Hb occurs frequently in invertebrate phyla as well. Many arthropod species use the copper-binding pigment hemocyanin, but unique in this phylum are the branchiopod crustaceans, which express Hb. Branchiopod Hb concentration and structure are exquisitely sensitive to environmental oxygen availability. Hemoglobin concentration and oxygen-binding affinity increase with decreasing oxygen tension in Daphnia, Artemia and Triops. The change in binding affinity is attributed to differential Hb subunit expression in Daphnia and Artemia but remains unclear for Triops. This is the first study to demonstrate developmental plasticity of Hb subunit expression in a notostracan, Triops longicaudatus, reared under conditions of varying oxygen availability. In response to variable oxygen environments, T. longicaudatus differentially express four primary Hb subunits ranging between 30 and 34 kDa, with normoxic-reared animals expressing primarily the heavier subunits, and hypoxic-reared animals expressing increased proportions of the lower molecular mass subunits. Moreover, differential Hb subunit expression is induced upon transfer of normoxic-reared adults to a hypoxic environment, such that the distribution of Hb subunits in the transferred adults becomes similar to that of hypoxic-reared animals. Two-dimensional gel electrophoresis and follow-up analyses revealed several isoforms of Hb subunits that may represent differential gene expression and/or post-translational modification. Unlike Daphnia and Artemia, the Hb hypoxic response in Triops is not reversible in that there was no significant decrease in Hb concentration or change in Hb subunit expression pattern when hypoxic-reared adults were transferred to a normoxic environment.

Physiological development of the embryonic and larval crayfish heart.

The cardiovascular system is the first system to become functional in a developing animal and must perform key physiological functions even as it develops and grows. The ontogeny of cardiac physiology was studied throughout embryonic and larval developmental stages in the red swamp crayfish Procambarus clarkii using videomicroscopic dimensional analysis. The heart begins to contract by day 13 of development (at 25 degrees C, 20 kPa O(2)). Cardiac output is primarily regulated by changes in heart rate because stroke volume remains relatively constant throughout embryogenesis. Prior to eclosion, heart rate and cardiac output decreased significantly. Previous data suggest that the decrease in cardiac parameters prior to hatching may be due to an oxygen limitation to the embryo. Throughout development, metabolizing mass and embryonic oxygen consumption increased, while egg surface area remained constant. The surface area of the egg membrane is a constraint on gas exchange; this limitation, in combination with the increasing oxygen demand of the embryo, results in an inadequate diffusive supply of oxygen to developing tissues. To determine if the decrease in cardiac function was the result of an internal hypoxia experienced during late embryonic development, early and late-stage embryos were exposed to hyperoxic water (PO(2) = 40 kPa O(2)). Heart rate in late-stage embryos exposed to hyperoxic water increased significantly over control values, which suggests that the suppression in cardiac function observed in late-stage embryos is due to a limited oxygen supply.

Allometric relationship of postmolt net ion uptake, ventilation, and circulation in the freshwater crayfish Procambarus clarkii: intraspecific scaling.

There are few intraspecific studies relating physiological parameters to body mass. This study relates scaling of ionic regulation and respiratory parameters with body mass in crayfish (Procambarus clarkii). These animals were chosen because of their direct development, spanning four orders of magnitude in body mass. Usually, these animals are hyperregulators and must maintain hemolymph electrolyte levels above those in the ambient freshwater. This is especially important in the postmolt, when ion imbalance can occur. Maintaining hemolymph ion levels above ambient involves active processes that are independently related to metabolic rate, ventilation, and circulation. Therefore, this study investigates relationships among size and ionic regulation, heart rate, and ventilation in crayfish, spanning a size range of 0.003-24 g. Postmolt net ion uptake of Ca, titratable base, Na, Cl, and NH4 increase with body mass (positive allometry) with slopes of 0.92, 0.79, 0.90, 0.84, and 0.87, respectively. Between 72% and 97% of variation in ionic regulation was related to body mass. The slopes differed from each other for Ca and titratable base but not for Na, Cl, and NH4. For heart rate and ventilation rate, different relationships were derived for animals smaller and larger than 0.01 g (between first and third instar). Animals larger than 0.01 g show a negative allometric relationship between heart rate and body size ([body mass](0.15)), while smaller animals show positive allometry with body size, but only 29% of variation in heart rate is explained by body size alone. For ventilation rates, the negative allometry with body size for animals larger than 0.01 g is present, but less than 15% of variation in ventilation rate is explained by size, while for smaller animals the size dependency disappears. Based on these results, predictions of physiological parameters such as ionic regulation based on body size are useful in crayfish, but estimates of respiratory parameters and body size should be used with caution.

Ontogeny of neurohormonal regulation of the cardiovascular system in the crayfish Procambarus clarkii.

Adult crayfish have a neurogenic heart which is modulated via inputs from the central nervous system and neurohormones, which act on the cardiac ganglion or directly on the myocardium. This study investigates the ontogeny of cardiac regulation by exploring the temporal sequence of cardiac sensitivity to injections of cardioactive neurohormones (proctolin, serotonin and octopamine) and the neurotransmitter gamma-aminobutyric acid. The cardiac response (delta in heart rate, stroke volume, or in cardiac output) to each neurohormone at each developmental stage was assessed. The observed response elicited by each cardioactive drug was stage dependent and changed as the animals progressed from embryonic through larval and juvenile periods. During early developmental stages, octopamine, serotonin, and proctolin (10(-9)-10(-3) M) did not result in a modulation of stroke volume, yet in later developmental stages they caused significant increases in stroke volume, at comparable concentrations. Early developmental stages are capable of regulating cardiac function, however, the mechanisms appear to be quite different from those used by adults. Evidence is also provided to support the hypothesis that cardiac function is initiated prior to the establishment of an adult-like regulatory system.

Perspectives on cardiac physiological ontogeny in crustaceans.

Crustacean embryonic and larval systems offer a unique and valuable tool for furthering our understanding of both developmental processes and physiological regulatory mechanisms. The diverse array of developmental patterns exhibited by crustaceans allows species choice to be based on the specific questions being investigated, where defined larval forms are chosen based on their developmental pattern, degree of maturation or regulatory capabilities. However, this great diversity in developmental patterns, as well as crustacean diversity, can also confound ones ability to define or identify species for investigation. These issues are addressed and suggestions put forth to clarify some of the problems. The complexity and overlapping nature of adult cardio-regulatory systems makes teasing them apart difficult. Embryonic and larval systems exhibit varying degrees of regulatory complexity depending on developmental stage and ontogenetic pattern. This can allow complex adult regulatory systems to be teased apart temporally, as the developing animal builds regulatory pathways. Equally important is the nature of crustacean larvae; many undergo dramatic metamorphoses in cases where the larvae have adaptations to environments different to those of the adult. During environmental transitions physiological adaptations to immediate change should take precedence over long-term adult adaptations. It is therefore possible to look at physiological responses as a function of developmental/environmental adaptation, independent of adult functions.

Integrated physiological responses to feeding in the blue crab Callinectes sapidus.

The passage of a barium meal (15 % by mass) was followed through the digestive system of the blue crab Callinectes sapidus by flash-freezing crabs at set intervals, followed by radiography of specimens. Food moved from the oesophagus into the stomach region within 15 min. After 1-2 h, food was visible in the midgut, at 6 h it had reached the hindgut, and material was still present in the stomach at this time. The stomach was emptied between 8 and 10 h after feeding, and the entire digestive system was cleared of material after 18 h. A pulsed-Doppler flowmeter was used to monitor cardiac variables and arterial haemolymph flows during a 4 h control and 24 h postprandial period. Heart rate increased immediately upon food detection and remained elevated for 16-18 h after food ingestion. There was no significant change in stroke volume of the heart, and total cardiac output increased significantly and remained elevated above pre-feeding levels for 24 h after feeding. There was no change in haemolymph flow through the anterior or posterior aorta, but flow increased in the sternal, anterolateral and hepatic arteries. These changes in haemolymph flow reflected the use of the chelae and mouthparts in feeding, contraction of the visceral muscle surrounding the gut system and mobilisation of enzymes from the hepatopancreas. There was also a postprandial increase in the rate of oxygen uptake (apparent specific dynamic action). The rate of oxygen consumption (M(dot)(O2)) reached maximal levels 4 h after feeding and decreased slowly thereafter, reflecting the increased use of oxygen in digestion and absorption.

Behavioral Physiology of Four Crab Species in Low Salinity.

Reports focusing on the behavioral responses of crabs to exposure to low salinity have involved choice chamber experiments or quantification of changes in activity. In addition to describing changes in locomotor activity in four species of crabs of differing osmoregulatory ability, the present study describes six behaviors: increased movement of the mouthparts, cleaning of the mouthparts with the chelae, cleaning of the antennae and antennules with the maxillipeds, flicking of the antennae, retraction of the antennules, and extension of the abdomen. Callinectes sapidus and Carcinus maenas are classed as efficient osmoregulators, and in general, showed an increase in these behaviors with decreasing salinity. Cancer magister, a weak regulator, and Libinia emarginata, an osmoconformer, exhibited these behaviors to a lesser degree and became inactive in the lower salinities, tending to adopt an isolation-type response. The differences in behaviors between the species correlated closely with previously reported changes in cardiovascular function and hemolymph flow. These overt reactions are discussed in relation to the osmoregulatory physiology and ecology of each crab species.

Heart rate during development in the turtle embryo: effect of temperature.

Growth and development can occur over a wide range of physical conditions in reptiles. Cardiovascular function must be critical to this ability. However, information on cardiovascular function in developing reptiles is lacking. Previous work indicated that in reptiles the effects of temperature on growth and metabolism are largely restricted to early development. This study examined whether the previously observed effects of temperature and different perinatal patterns of metabolism observed in amniotic vertebrates are correlated with cardiovascular function. Embryonic and hatchling carcass mass, heart mass and heart rate (HR) were compared for snapping turtle eggs (Chelydra serpentina) incubated at 24 degrees and 29 degrees C. Incubation time was shorter at 29 degrees C (56.2 days) than at 24 degrees C (71.1 days). Carcass and heart growth showed a sigmoidal pattern at both temperatures. However, cardiac growth showed a relative decrease as incubation proceeded. Incubation temperature significantly affected the HR pattern during development. The HR of embryos incubated at 24 degrees C was constant for most of incubation (51.8 +/- 4.8 min-1). A small decrease was observed just prior to and a large decrease immediately following hatching (posthatch, 22.3 +/- 4.1 min-1). At 29 degrees C embryonic HR was greater than at 24 degrees C early in development (72.3 +/- 3 min-1). The HR steadily decreased to values equivalent to those at 24 degrees C. The HRs of 24 degrees C and 29 degrees C hatchlings were not different. Cardiac output (estimated as the product of heart mass and HR) increased rapidly during early development and then slowed dramatically at both temperatures. These data are consistent with the suggestion that temperature exerts its effects primarily early in development. Furthermore, the changes in cardiovascular function are correlated with metabolic changes in hatching vertebrates.