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At least 433 records · Page 24Linked to original sources
PubMed1979

Shark heart mitochondria: effects of external osmolality on respiration.

Shark mitochondrial respiration was studied in media with osmolalities between 160 and 1500 milliosmoles. The respiratory control ratio, a marker for functional integrity of the isolated mitochondria, was maximal at 1000 millismoles and decreased during hypotonic or hypertonic exposure. Shark mitochondria function best at their native tonicity, a value that produces abnormal function in mammalian mitochondria.

Adenosine Diphosphate↗
PubMed1993

Cl- secretion by cultured shark rectal gland cells. III. Ca2+ regulation of apical membrane Cl- conductance.

Calcium ionophores (ionomycin and A-23187) were employed to assess the effects of increased intracellular Ca2+ concentration ([Ca2+]i) on apical membrane Cl- conductance (GaCl) and rate of transepithelial Cl- secretion in cultured shark rectal gland (SRG) cells. Apical 2 microM ionomycin induced dramatic changes in cellular electrophysiological properties: the apical membrane electrical potential difference (V(a)) depolarized from -66 mV to -46 mV, the fractional resistance of the apical membrane (fRa) decreased from 0.88 to 0.23, and the transepithelial electrical potential difference (Vab) increased slightly from +1.2 mV to +1.4 mV. These effects result from increased GaCl because apical low-Cl- shark Ringer (SR) depolarized V(a) by 32 mV and increased fRa from 0.23 to 0.36. Ionomycin-stimulated Vab or short-circuit current (Isc) results largely from increased Cl- secretion because approximately 80% of the increase in Isc is Cl- dependent. Establishing the Ca2+ dependence of ionophore activation of GaCl was confounded because apical low-Ca2+ SR [Ca2+ concentration ([Ca2+]) 1 mM to 0.1 microM] alone activated this conductive pathway. To establish the Ca2+ dependence of ionophore action, we assessed the effect of ionomycin on Isc in low-Ca2+ SR ([Ca2+] = 0.1 microM) and in SR. In low-Ca2+ SR, apical ionomycin stimulated Isc by 14.0 microA/cm2. In SR (normal [Ca2+]), ionomycin increased Isc further by 27.0 microA/cm2. Superfusing the basolateral surface with 2 microM ionomycin for 8-16 min failed to activate GaCl. In every case, subsequent superfusion of the apical surface with ionophore for 1.5-2 min activated GaCl. Bilateral 4 microM indomethacin (45-min superfusion) failed to block the ionomycin-induced GaCl.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Digital image analysis of shark gills: modeling of oxygen transfer in the domain of time.

Digital radiographic imaging of blood circulation through leopard shark gills establishes a secondary lamellar transit time of 6.5 s. This duration, combined with estimates of cardiac output and hemoglobin-oxygen affinity, permits novel modeling of gill oxygen transfer in the time domain. The temporal model allows assessment of factors contributing to previously noted discrepancies between physiological and morphometric branchial oxygen conductance estimates. Lamellar transit time for shark blood is 20 times greater than human alveolar transit time, and thus correlates with a slower rate of hemoglobin-oxygen binding and a greater diffusion distance.

Animals↗
PubMed1997

Role of guanylyl cyclase receptors for CNP in salt secretion by shark rectal gland.

The role of C-type natriuretic peptide (CNP) and its guanylyl cyclase-linked receptors in mediating salt secretion by the rectal gland of the spiny dogfish shark (Squalus acanthias) was investigated using HS-142-1, a competitive inhibitor of the binding of natriuretic peptides to their guanylyl cyclase receptors. CNP binds to receptors and activates guanylyl cyclase in rectal gland membranes in a way that is inhibited by HS-142-1. Guanylyl cyclase activation in rectal gland membranes is far more sensitive to CNP than to atrial natriuretic peptide, whereas the reverse is true for membranes derived from mammalian (rabbit) renal collecting duct cells. HS-142-1 inhibited the stimulatory effect of CNP on ouabain-inhibitable oxygen consumption by rectal gland tubules. In explanted rectal glands continuously perfused with blood from intact donor sharks, HS-142-1 inhibited the increase in salt secretion normally provoked by infusing isotonic saline solutions into the donor animal. These results strongly support the view that CNP released into the systemic circulation in response to volume expansion mediates the secretion of chloride by the rectal gland via receptors linked to guanylyl cyclase.

Adenylyl Cyclases↗
PubMed1998

A prostaglandin, not NO, mediates endothelium-dependent dilation in ventral aorta of shark (Squalus acanthias).

In mammals, the vascular endothelium releases a variety of paracrine factors, including the vasodilatory prostaglandin (PG)I2 and nitric oxide (NO), which is generally accepted as the major endothelium-derived relaxing factor (EDRF) in mammals. Current evidence for the vascular NO-EDRF system in fishes is contradictory. In addition, the role of PGs in the control of fish vascular tension is also unclear. We have utilized isolated rings of the ventral aorta of the spiny dogfish shark to examine the ability of various components of the NO system to dilate this vessel. Neither the NO precursor L-arginine, the NO donor sodium nitroprusside, nor NO itself dilated the rings. The Ca2+ ionophore A-23187 did produce an endothelium-dependent dilation that was not inhibited by the NO synthase inhibitor NG-nitro-L-arginine methyl ester but was inhibited by the cyclooxygenase inhibitor indomethacin, suggesting that PGs are involved. PGE1 and carbaprostacyclin, but not PGI2, produced concentration-dependent dilation, and intact aortic rings secreted five times as much PGI2 as PGE in both the unstimulated state and after stimulation with A-23187. Our data suggest strongly that a PG, most probably PGI2, is the EDRF in the ventral aorta of this shark species.

Alprostadil↗
PubMed1988

Secretion of endolymph by semicircular canals of the shark.

The semicircular canals of the vestibular labyrinth of the dogfish shark, Squalus acanthias, may serve as a simple in vitro system for the study of the ionic transport mechanisms involved in endolymph formation. Electron microscopy showed that the epithelium was made up of at least three distinct cell types divided into separate regions running the length of the canals. Secretion of endolymph was studied in isolated canals by the split droplet method; when the lumens of the canals were filled with shark Ringer a potassium-rich fluid was secreted into the lumen at a rate of 0.34 microliter.cm-2.min-1. The K concentration of the secreted fluid averaged 112 mM; the calculated rate of K secretion was 2.3 mumol.cm-2.h-1, comparable to recent measurements in mammalian utricle. Fluid secretion was dependent on active transport and was inhibited by ouabain, bumetanide, or methazolamide in the external bathing solution. Fluid secretion was unaffected by the K channel blocker, Ba, in the luminal droplet or by the adenylate cyclase stimulator, forskolin, in the external bathing solution. For electrophysiological analysis, isolated canals were perfused in a chamber designed for voltage/current clamping; an axial wire was inserted into the canal lumen and constant-current pulses were passed to determine tissue resistance. When the luminal fluid was high-K Ringer, transepithelial potential difference was -1.1 mV (lumen negative) and resistance 37 omega.cm2. Dilution and bi-ionic potential measurements showed that the epithelium of the canals exhibited only slight cation selectivity. These results are consistent with a model for endolymph secretion involving cotransport secondary to the ion gradients created by the Na+-K+-ATPase.

Animals↗
PubMed2002

Association of GM4 ganglioside with the membrane surrounding lipid droplets in shark liver.

By TLC, GM4 was found to be the major ganglioside in the liver of six shark species examined: Odontaspis taurus, Negaprion brevirostris, Sphyrna lewini, Mustelus griseus, Mustelus manazo, and Prionace glauca. A detailed analysis of the glycosphingolipids (GSLs) in the liver of O. taurus (sand tiger shark) showed that it contained approximately 110 nmol of lipid-bound sialic acid per gram of wet tissue, of which 80% was GM4. By extracting the liver of O. taurus with chloroform/methanol, followed by chromatographic separation of GSLs using DEAE-Sephadex A-25 and Iatrobeads columns, we have isolated GM4 in pure form with a yield of approximately 5 mg per 100 g of wet tissue. The structures of both the sugar chain and the ceramide moiety of this GM4 were analyzed by chemical analysis, mass spectrometry, and NMR spectroscopy. Similar to GM4 isolated from other sources, 92% of fatty acids in the ceramide of this GM4 were 2-hydroxylated. However, unlike the long-chain bases found in other GSLs, the total long-chain bases in this GM4 were found to contain 43% octadecasphingenine and 50% nonadecasphingenine. Immunohistochemical analysis using a monoclonal antibody against GM4 revealed that the hepatocytes of both M. griseus (spotless smooth hound) and M. manazo (smooth hound) were filled with lipid droplets and GM4 was primarily associated with the membrane structure surrounding lipid droplets.

Animals↗
PubMed2004

Hypoxic survival strategies in two fishes: extreme anoxia tolerance in the North European crucian carp and natural hypoxic preconditioning in a coral-reef shark.

Especially in aquatic habitats, hypoxia can be an important evolutionary driving force resulting in both convergent and divergent physiological strategies for hypoxic survival. Examining adaptations to anoxic/hypoxic survival in hypoxia-tolerant animals may offer fresh ideas for the treatment of hypoxia-related diseases. Here, we summarise our present knowledge of two fishes that have evolved to survive hypoxia under very different circumstances. The crucian carp (Carassius carassius) is of particular interest because of its extreme anoxia tolerance. During the long North European winter, it survives for months in completely oxygen-deprived freshwater habitats. The crucian carp also tolerates a few days of anoxia at room temperature and, unlike anoxia-tolerant freshwater turtles, it is still physically active in anoxia. Moreover, the crucian carp does not appear to reduce neuronal ion permeability during anoxia and may primarily rely on more subtle neuromodulatory mechanisms for anoxic metabolic depression. The epaulette shark (Hemiscyllium ocellatum) is a tropical marine vertebrate. It lives on shallow reef platforms that repeatedly become cut off from the ocean during periods of low tides. During nocturnal low tides, the water [O(2)] can fall by 80% due to respiration of the coral and associated organisms. Since the tides become lower and lower over a period of a few days, the hypoxic exposure during subsequent low tides will become progressively longer and more severe. Thus, this shark is under a natural hypoxic preconditioning regimen. Interestingly, hypoxic preconditioning lowers its metabolic rate and its critical P(O(2)). Moreover, repeated anoxia appears to stimulate metabolic depression in an adenosine-dependent way.

Adaptation, Physiological↗
PubMed2004

Adenosinergic and cholinergic control mechanisms during hypoxia in the epaulette shark (Hemiscyllium ocellatum), with emphasis on branchial circulation.

Coral reef platforms may become hypoxic at night during low tide. One animal in that habitat, the epaulette shark (Hemiscyllium ocellatum), survives hours of severe hypoxia and at least one hour of anoxia. Here, we examine the branchial effects of severe hypoxia (<0.3 mg oxygen l(-1) for 20 min in anaesthetized epaulette shark), by measuring ventral and dorsal aortic blood pressure (P(VA) and P(DA)), heart rate (fh), and observing gill microcirculation using epi-illumination microscopy. Hypoxia induced a flow of blood in two parallel blood vessels, termed longitudinal vessels, in the outer borders of the free tip of the gill filament. Hypoxia also induced significant falls in fh, P(VA) and P(DA), and a biphasic change in ventilation frequency (increase followed by decrease). Adenosine injection (1 micromol kg(-1)) also initiated blood flow in the longitudinal vessels, in addition to significant drops in P(VA), P(DA) and fh, and a biphasic response in ventilation frequency (decrease followed by increase) indicating that adenosine influences ventilation. Aminophylline (10 mg kg(-1)), an A(1) and A(2) adenosine receptor antagonist, blocked the effects of adenosine injection, and also significantly reduced blood flow in the longitudinal vessels during hypoxia. In the second part of the study, we examined the cholinergic influence on the cardiovascular circulation during severe hypoxia (<0.3 mg l(-1)) using antagonists against muscarinic (atropine 2 mg kg(-1)) and nicotinic (tubocurarine 5 mg kg(-1)) receptors. Injection of acetylcholine (ACh; 1 micromol kg(-1)) into the ventral aorta caused a marked fall in fh, a large increase in P(VA), but small changes in P(DA) (suggesting increased R(gill)). Atropine was able to inhibit the branchial vascular responses to ACh but not the hypoxic bradycardia, suggesting the presence of muscarinic receptors on the heart and gill vasculature, and that the hypoxia induced bradycardia is of non-cholinergic origin. The results suggest that adenosine mediates increases in the arterio-venous circulation in the gill during hypoxia. This may serve to increase blood supply to heart and gill tissue.

Acetylcholine↗
PubMed2000

Durophagy in sharks: feeding mechanics of the hammerhead Sphyrna tiburo.

This study investigates the motor pattern and head movements during feeding of a durophagus shark, the bonnethead Sphyrna tiburo, using electromyography and simultaneous high-speed video. Sphyrna tiburo feeds almost exclusively on hard-shelled crabs, with shrimp and fish taken occasionally. It captures crabs by ram feeding, then processes or reduces the prey by crushing it between molariform teeth, finally transporting the prey by suction for swallowing. The prey-crushing mechanism is distinct from that of ram or bite capture and suction transport. This crushing mechanism is accomplished by altering the duration of jaw adductor muscle activity and modifying jaw kinematics by the addition of a second jaw-closing phase. In crushing events, motor activity of the jaw adductor muscles continues (biting of the prey occurs as the jaws close and continues after the jaws have closed) throughout a second jaw-closing phase, unlike capture and transport events during which motor activity (biting) ceases at jaw closure. Sphyrna tiburo is able to take advantage of a resource (hard prey) that is not readily available to most sharks by utilizing a suite of durophagous characteristics: molariform teeth, a modified jaw protrusor muscle, altered jaw adductor activity and modified jaw kinematics. Sphyrna tiburo is a specialist feeder on crab prey as demonstrated by the lack of differences in kinematic or motor patterns when offered prey of differing hardness and its apparent lack of ability to modulate its behavior when feeding on other prey. Functional patterns are altered and coupled with modifications in dental and jaw morphology to produce diverse crushing behaviors in elasmobranchs.

Animals↗
PubMed2001

Water-tunnel studies of heat balance in swimming mako sharks.

The mako shark (Isurus oxyrinchus) has specialized vascular networks (retia mirabilia) forming counter-current heat exchangers that allow metabolic heat retention in certain regions of the body, including the aerobic, locomotor red muscle and the viscera. Red muscle, white muscle and stomach temperatures were measured in juvenile (5-13.6 kg) makos swimming steadily in a water tunnel and exposed to stepwise square-wave changes in ambient temperature (T(a)) to estimate the rates of heat transfer and to determine their capacity for the activity-independent control of heat balance. The rates of heat gain of red muscle during warming were significantly higher than the rates of heat loss during cooling, and neither the magnitude of the change in T(a) nor the direction of change in T(a) had a significant effect on red muscle latency time. Our findings for mako red muscle are similar to those recorded for tunas and suggest modulation of retial heat-exchange efficiency as the underlying mechanism controlling heat balance. However, the red muscle temperatures measured in swimming makos (0.3-3 degrees C above T(a)) are cooler than those measured previously in larger decked makos. Also, the finding of non-stable stomach temperatures contrasts with the predicted independence from T(a) recorded in telemetry studies of mako and white sharks. Our studies on live makos provide new evidence that, in addition to the unique convergent morphological properties between makos and tunas, there is a strong functional similarity in the mechanisms used to regulate heat transfer.

Animals↗
PubMed1997

The analgesic and anti-inflammatory effects of shark cartilage are due to a peptide molecule and are nitric oxide (NO) system dependent.

The present work shows an antinociceptive and dose-dependent effect of shark cartilage hydrosoluble fraction (HF) on writhing and formalin tests in mice. The effect was not altered by thalidomide, a known inhibitor of tumor necrosis factor-alfa (TNF-alfa) synthesis. Similarly, the antinociceptive effect did not change in the presence of naloxone, indicating that the opioid system is not involved. However, the effect observed was blocked by L-arginine, a NO synthesis substrate, and it was potentiated by L-NAME, suggesting a role of the NO system in the shark cartilage antinociceptive effect. Effects similar to those seen with the HF were detected with peak II from gel filtration chromatography. The increase in vascular permeability induced by serotonin in rats was significantly abolished by the HF at the dose of 2 mg/kg, p.o., and again it was not potentiated by thalidomide. The observed blockade in the vascular permeability increase induced by histamine was detected only with a higher dose (10 mg/kg, p.o.).

Analgesics↗
PubMed1996

Separation of anti-shark type I collagen antibody from anti-pig type I collagen antiserum and its partial characterization.

Anti-shark type I collagen antibody (PAb-S) was successfully separated from anti-pig type I collagen antiserum. PAb-S recognized a chymotryptic peptide (29 kDa) of alpha 1 (I) chain prepared from shark skin. This result suggested that the epitope contained in this chymotryptic peptide may be well conserved during the molecular evolution of type I collagen.

Animals↗
PubMed2000

Mercury content in shark species from the South-Eastern Brazilian coast.

We present here the first results of Hg concentrations in three small shark species (Rhizoprionodon lalandei, R. porosus and Mustelus higmani) from the SE Brazilian coast. Mercury concentrations in R. lalandei ranged from 21.5 to 280.0 ng.g-1 dry weight (d.w.) (average 74.6 ng.g-1 d.w.; 17.9 ng.g-1 wet weight). In R. porosus, concentrations ranged from 7.6 to 90.5 ng.g-1 d.w. (average 42.2 ng.g-1 d.w., 9.4 ng.g-1 wet weight), whereas in M. higmani, concentrations ranged from 13.0 to 162.8 ng.g-1 d.w. (average 54.9 ng.g-1 d.w., 13.4 ng.g-1 wet weight). These concentration ranges are very low compared with values reported for other large shark species of the Southwestern Atlantic Ocean. There was a significant positive correlation between Hg concentrations and individual size, suggesting that biomagnification is occurring in these animals.

Animals↗
PubMed2001

Kroeyerina deetsorum n. sp. (Copepoda: Kroyeriidae) from the olfactory sacs of Atlantic sharpnose sharks (Rhizoprionodon terraenovae) captured in the Gulf of Mexico and northwestern Atlantic and first report of copepodids representing Kroyeriidae.

Kroeyerina deetsorum n. sp. (Copepoda: Kroyeriidae) is described from female and male specimens collected from the olfactory sacs of Atlantic sharpnose sharks, Rhizoprionodon terraenovae (Richardson, 1836), captured in the Gulf of Mexico and northwestern Atlantic. Kroeyerina deetsorum is easily distinguished from known congeners by the extremely small size of its adults (i.e., females about 1.2 mm total length and males about 1.0 mm total length). Kroeyerina deetsorum is also distinguished from its congeners by possessing a subquadrate rostrum without lobes or upturned horns. It is suspected that K. deetsorum belongs to a clade within Kroeyerina whose members only infect sharks. This report also provides first descriptions of a nauplius representing Kroeyerina and copepodids representing Kroyeriidae. The early-stage copepodid of K. deetsorum lacks a frontal organ and frontal filament and uses its chelate antennae to attach to its host.

Animals↗
PubMed2003

New records for Dinemoura ferox (Copepoda: Siphonostomatoida: Pandaridae) from Pacific sleeper sharks captured in waters off eastern Taiwan.

Four of the 27 Pacific sleeper sharks (Somniosus pacificus Bigelow and Schroeder) captured in the western North Pacific Ocean off eastern Taiwan between 19 March and 18 May 2002 hosted the parasitic copepod Dinemoura ferox (Krøyer, 1838) on their body surface including the fins. This report documents a new host record as well as a new ocean record for D. ferox, which until now has only been reported from the benthopelagic sharks, Somniosus microcephalus (Bloch and Schneider) and Centrophorus squamosus (Bonnaterre), occurring in the north Atlantic Ocean off Greenland and Iceland.

Animals↗
PubMed2006

Two new species of Paraorygmatobothrium (Cestoda: Tetraphyllidea) from weasel sharks (Carcharhiniformes: Hemigaleidae) of Australia and Borneo.

Two new species of Paraorygmatobothrium Ruhnke, 1994, P. janineae n. sp. and P. kirstenae n. sp., are described from the spiral intestine of 2 shark species of the Family Hemigaleidae: Hemigaleus microstoma and Hemipristis elongata. The 2 new cestode species differ from other members of Paraorygmatobothrium in vitelline follicle distribution and possession of a cephalic peduncle. The 2 new species differ from 1 another in total length, maximum width, scolex size, number of proglottids per strobila, and number of testes per proglottid. The generic diagnosis of Paraorygmatobothrium is emended to include the new species. The results of this study extend the distribution of Paraorygmatobothrium to include the carcharhinid shark family Hemigaleidae.

Animals↗
PubMed1986

Immunohistochemical localization of urotensins I and II in the caudal neurosecretory neurons of the carp Cyprinus carpio and the sharks Heterodontus japonicus and Cephaloscyllium umbratile.

Using antisera to urotensins I and II (UI and UII), in the carp, Cyprinus carpio, three types of caudal neurosecretory neurons were identified: those with both UI- and UII-immunoreactivities, those with only UI-immunoreactivity and those with only UII-immunoreactivity. The last type of neurons exceeded the other types in number, while neurons immunoreactive with both UI and UII antisera were relatively few. The axons of neurons of these three types terminated around the capillaries in the urophysis. In the cat shark, Heterodontus japonicus and the swell shark, Cephaloscyllium umbratile, two types of neurons were identified: those with both UI- and UII-immunoreactivities and those with only UII-immunoreactivity. Neurons of the former type were greater in number than the latter. The axons of neurons of both types terminated in the neurohemal areas.

Animals↗