Biochemical characteristics and modulation by external and internal factors of aminopeptidase-N activity in the hepatopancreas of a euryhaline burrowing crab

The role of the renin-angiotensin system (RAS) in salinity adaptation in Pacific white shrimp (Litopenaeus vannamei)

The renin-angiotensin system (RAS) is a hormonal system that plays an important role in the regulation of blood pressure and cardiovascular homeostasis in mammals. In fishes, the RAS pathway participates in osmoregulation and salinity adaptation. However, the role of the RAS pathway in invertebrates, particularly in crustaceans, remains unknown. In this study, four key genes of the RAS pathway (LV-ACE, LV-APN, LV-AT1R, and LV-RR) were cloned, characterized, and their expression levels were detected in the eyestalk, hepatopancreas, and muscle of Litopenaeus vannamei during long-term and short-term low salinity stress. The results showed that LV-ACE, LV-APN, LV-AT1R, and LV-RR encode 666, 936, 175, and 323 amino acids, respectively. Low salinity stress downregulated the expression levels of LV-ACE, LV-APN, LV-AT1R, and LV-RR in L. vannamei, indicating that the RAS pathway was suppressed under low salinity. Moreover, these genes play important roles in the regulation of drinking rate, controlling urine output, blood glucose, and blood pressure, indicating that their downregulation probably affected the homeostasis of shrimps. These findings provide novel insights into the mechanism of salinity adaptation in L. vannamei.

Prejuveniles of Mugil liza (Actinopterygii; Fam. Mugilidae) show digestive and metabolic flexibility upon different postprandial times and refeeding

Many animals face periods of feeding restrictions implying fasting and refeeding. The determination of digestive/metabolic and body condition parameters at different times of food deprivation and after refeeding allows to evaluate the postprandial dynamics, the transition from feeding to fasting and the capacity to reverse digestive and metabolic alterations. In spite of its physiological importance, studies on estuarine-dependent detritivore fish are lacking. We determined total mass (TM), relative intestine length (RIL), hepatosomatic index (HSI), digestive enzymes activities in the intestine and energy reserves in liver and muscle at 0, 24, 72, 144 and 240 h after feeding and at 72 h after refeeding in prejuveniles of Mugil liza (Mugilidae) as a model species. After feeding, a decrease occurred in: TM (144 h, 25%), RIL (144 h, 23%); amylase and maltase (72 h, 45 and 35%), sucrase (24 h, 40%) and lipase (24 h, 70%) in intestine; glycogen and free glucose (72 h, 90 and 92%) in liver. In muscle, glycogen (72-144 h) and free glucose (144 h) (170% and 165%, respectively) peak increased; triglycerides decreased at 24-240 h (50%). After refeeding TM, RIL, carbohydrases activities in intestine, glycogen and free glucose in liver were recovered. In muscle, glycogen and free glucose were similar to 0 h; lipase activity and triglycerides were not recovered. Trypsin and APN in intestine, triglycerides in liver, protein in liver and muscle and HSI did not change. The differential modulation of key components of carbohydrates and lipid metabolism after feeding/refeeding would allow to face fasting and recover body condition. Our results improve lacking knowledge about digestive and metabolic physiology of detritivore fish.

Understanding the early ontogenetic stages of Mugil liza (Mugilidae): Morphological traits and digestive/metabolic profile of pre-juveniles after recruitment

The family Mugilidae consists mainly of diadromous species, whose reproduction occurs in offshore waters. Pre-juveniles shift their diet in the surf zone (zooplanktophagous to iliophagous). Later, during their recruitment into estuaries, huge changes take place in their digestive system. However, digestive and metabolic characteristics and some morphological traits at recruitment are unknown for Mugilidae. We performed comparative studies on early and late pre-juveniles of Mugil liza recruited in Mar Chiquita Coastal Lagoon (37°32'-37°45'S, 57°19'-57°26'W, Argentina). We determined digestive enzyme activities (intestine), energy reserves (liver/muscle), total/standard length, total weight, intestinal coefficient, hepatosomatic index and retroperitoneal fat. Pre-juveniles exhibited amylase, maltase, sucrase, lipase, trypsin and aminopeptidase-N (APN) activities, which were maintained over a wide range of pH and temperature, and exhibited Michaelis-Menten kinetics. In late pre-juveniles, amylase (422 ± 131 μmol maltose min^-1 mgprot^-1 ), sucrase (86 ± 14 mg glucose min^-1 mgprot^-1 ), trypsin (84 ± 9 μmoles min^-1 mgprot^-1 ) and APN (0.58 ± 0.08 μmoles min^-1 mgprot^-1 ) activities were higher (42%, 28%, 35% and 28%, respectively) than in the early stage. Also, the intestinal coefficient was higher in late (3.04) compared to early (2.06) pre-juveniles. Moreover, the liver appeared to be a main site of glycogen and triglyceride storage in late pre-juveniles, muscle being the site of storage in early pre-juveniles, exhibiting higher glycogen, free glucose and protein concentrations (92%, 82%, 32%, respectively). The results suggest that pre-juveniles of M. liza exhibit an adequate digestive battery to perform complete hydrolysis of various dietary substrates, availability of energy reserves and morphological characteristics to support their feeding habit and growth after recruitment. Our results represent an important contribution to knowledge of the ecology and digestive physiology of pre-juveniles of Mugilidae in the wild.

Differential modulation after feeding in different salinities and response to abscisic acid (ABA) and extracellular Ca2+ of aminopeptidase N (APN) activity in the hepatopancreas of the intertidal euryhaline crab Neohelice granulata

Modulation of aminopeptidase N (APN) activity in the digestive tract by various factors would be important to adjust digestive and absorptive processes under different physiological and (or) environmental conditions. We studied the postprandial responses at different salinities and the effect of abscisic acid (ABA) and extracellular Ca2+ on APN activity in the hepatopancreas (the main site for nutrient digestion and absorption) of the model species Neohelice granulata (Dana, 1851). Enzyme activity was determined at different times (0, 24, 48, and 72 h) after feeding in crabs acclimated either to 35 psu (osmoconformation) or 10 psu (hyper-regulation). APN activity increased around 50% at 24 h after feeding at 35 psu, whereas no changes occurred at 10 psu. Enzyme activity was also assayed in the presence of ABA (1 × 10–4 mol·L–1) or extracellular Ca2+ (1 × 10–4 mol·L–1), showing increments of 60% and 56%, respectively. The results suggest a role of APN in postprandial adjustments and its modulation by different chemical messengers by direct effect on the hepatopancreas. Moreover, to our knowledge, this work is the first to show the effect of ABA on a digestive enzyme in the digestive tract of an animal.

Two sodium pumps in the hepatopancreas of the intertidal euryhaline crab Neohelice granulata: biochemical characteristics and differential modulation after feeding

No study has been done on the existence, biochemical characteristics, and modulation of K+-independent ouabain-insensitive Na+ ATPase activity (the second sodium pump) in the digestive tract of intertidal euryhaline crabs and moreover on the coexistence and modulation under distinct physiological and (or) environmental conditions of different sodium pumps. We determined the occurrence, characteristics, and responses at different times (0, 1, 24, 48, and 120 h) after feeding upon distinct salinities of Na+ ATPase activity and Na+/K+ ATPase in the hepatopancreas of Neohelice granulata (Dana, 1851), which is a model species. The stimulation by Na+ under total inhibition of Na+/K+ ATPase activity revealed the occurrence of Na+ ATPase activity that was totally inhibited by 2 mmol·L–1 furosemide, exhibits Michaelis–Menten kinetics for ATP (apparent Km = 0.52 ± 0.16 mmol·L–1), and highest activity at around pH 7.4. In crabs acclimated to 35 psu (osmoconforming conditions), Na+ ATPase activity was highly increased (about 15-fold) (532 ± 58 nmol Pi·mg protein−1·min−1) in the hepatopancreas 48 h after feeding. In 10 psu (hyper-regulating conditions), Na+ ATPase activity decreased in the hepatopancreas 24 h after feeding (7 ± 9 nmol Pi·mg protein−1·min−1) and recovered initial values after 48 h (24 ± 35 nmol Pi·mg protein−1·min−1). Unlike Na+ ATPase, Na+/K+ ATPase activity did not change after feeding at any salinity, suggesting the specific modulation of the second sodium pump and its role in postprandial adjustments in the hepatopancreas.

In silico analysis and effects of environmental salinity in the expression and activity of digestive α-amylase and trypsins from the euryhaline crab Neohelice granulata

Studies on molecular characteristics and modulation of expression of α-amylase and trypsin in the hepatopancreas of intertidal euryhaline crabs are lacking. In this work, we cloned and studied by in silico approaches the characteristics of cDNA sequences for α-amylase and two trypsins isoforms, as well as the effect of environmental salinity, on gene expression and protein activities in the hepatopancreas of Neohelice granulata (Dana, 1851), which is a good invertebrate model species. The cDNA sequence of α-amylase is 1637 bp long, encoding 459 amino acid residues. Trypsin 1 and 2 are 689 and 1174 bp long, encoding 204 and 151 amino acid residues, respectively. Multiple sequence alignment of deduced protein sequences revealed the presence of conserved motifs found in other invertebrates. In crabs acclimated at 37 psu (hyporegulation), α-amylase mRNA level and total pancreatic amylase activity were higher than at 10 psu (hyperregulation) and 35 psu (osmoconformation). Trypsin 1 mRNA levels increased at 37 psu, while trypsin 2 levels decreased at 10 and 37 psu. Total trypsin activity was similar in all salinities. Our results showed a differential modulation of α-amylase and trypsin expression and total amylase activity by salinity acclimation, suggesting the occurrence of distinct mechanisms of regulation at different levels that could lead to digestive adjustments in relation to hyperregulation and (or) hyporegulation.