Showing papers by "Mount Desert Island Biological Laboratory published in 1992"
TL;DR: It is suggested that ovarian progesterone (follicular or luteal in origin) has a dual role in the evolution of viviparity: to inhibit myometrial contractions, thus providing a primary condition for egg retention and v Viviparity.
Abstract: For the past 25 years we have used a comparative strategy designed to identify anddescribe the endocrine parameters of the oviparous-vivparous transition and subsequent gradual reduction in hepatic yolk protein precursor (vitellogenin) synthesis associated with placental viviparity. Our approach has been to study vertebrate groups in which both oviparous and viviparous modes are common (reptiles, elasmobranchs). We have provided evidence for the control of follicular (granulosa/theca) and luteal steroidogenesis, and the cellular basis of gonadal steroid hormone action on the key target tissues (oviduct, liver). Our results, some of which are summarized below, have led us to suggest that ovarian progesterone (follicular or luteal in origin) has a dual role in the evolution of viviparity: 1. To inhibit myometrial contractions, thus providing a primary condition for egg retention and viviparity. 2. To inhibit estrogen-induced hepatic vitellogenin synthesis as part of both normal oviparous cycles and as a concomitant of placental evolution.
103 citations
TL;DR: Several lines of evidence point to the contribution of gill Na+/NH4+ exchange to the total ammonia excreted during hypercapnia, whereas NH3 diffusion predominates during the recovery period, whereas Cl−/HCO3− or Cl−/(OH−/OH− exchange may enhance the uptake of HCO3 −-equivalent duringHypercapnia.
Abstract: The effect of hypercapnia on the acid-base balance and acid-equivalent transfers has been measured in the dogfish Squalus acanthias. Previous reports on Squalus are not in agreement as to the role played by compensatory acid-base transfers between the animal and the water during hypercapnia.
Cannulated animals were maintained in a closed circuit, seawater recirculation system. Plasma pH, Cco2 (from which Pco2 and [HCO3−] were calculated), and transfers of NH4+ and HCO3−-equivalent ions between the fish and the water, were measured during 24 hours of hypercapnic exposure (Pco2: 8–10 torr) and a subsequent 8–24 hour normocapnic recovery period.
Respiratory acidosis resulted in a plasma pH depression, which was then almost completely compensated (within ˜ 0.1 pH unit) over 24 hours by a ˜ 20 mM increase in plasma [HCO3 ]. In contrast to previous studies on elasmobranch acid-base regulation, hypercapnia induced a rapid 3 × increase in not only HCO3−-equivalent uptake but also branchial ammonia (NH4+) excretion. These transfers combined for a net Δ H+ loss to the water of 5.5 mmol kg−1. During the normocapnic period, net Δ H+ was reversed to −6.9 mmol kg−1, nearly completely due to HCO3-efflux.
Several lines of evidence point to the contribution of gill Na+/NH4+ exchange to the total ammonia excreted during hypercapnia, whereas NH3 diffusion predominates during the recovery period. Likewise, Cl−/HCO3− or Cl−/OH− exchange may enhance the uptake of HCO3− during hypercapnia.
65 citations
TL;DR: The binding of [3H]benzmetanide to secretory tubules isolated from dogfish shark rectal glands suggested that separate signal transduction pathways, one sensitive to cAMP and another to cell volume, regulate the Na-K-Cl cotransporter.
Abstract: We examined the binding of [3H]benzmetanide, a potent inhibitor of Na-K-Cl cotransport, to secretory tubules isolated from dogfish shark rectal glands. Specific binding increased dramatically (from...
58 citations
TL;DR: Binding of the loop diuretic [3H]benzmetanide to the intact gland is examined, providing strong evidence that the Na-K-Cl cotransport system is activated as part of the process of stimulation of secretion.
Abstract: To investigate regulation of the Na-K-Cl cotransport system in the rectal gland of the dogfish shark Squalus acanthias, we examined binding of the loop diuretic [3H]benzmetanide to the intact gland. Glands were perfused with a shark Ringer solution, either in a basal state or stimulated with vasoactive intestinal peptide (VIP). [3H]benzmetanide was added to the perfusion solution for the last 25 min of perfusion, after which the gland was homogenized and the amount of bound [3H]benzmetanide was determined in the membrane fraction. Most of the membrane-associated [3H]-benzmetanide appeared to be associated with the Na-K-Cl cotransporter as judged by the dissociation rates at 0 degree C and 20 degrees C, by labeling with a photosensitive analogue, and by continued association of [3H]benzmetanide with membrane protein on solubilization. With the use of [3H]4-benzoyl-5-sulfamoyl-3-(3- thenyloxy)benzoic acid, a photosensitive analogue of benzmetanide, a 200-kDa protein was selectively labeled on exposure to ultraviolet light. It was also possible to detect [3H]-benzmetanide binding during the perfusion period as an arterial-venous difference, thereby providing a time course of the binding process. In comparing two groups of five glands each, VIP stimulated NaCl secretion 20-fold and [3H]benzmetanide binding 16-fold, providing strong evidence that the Na-K-Cl cotransport system is activated as part of the process of stimulation of secretion. The VIP-stimulated increase in [3H]benzmetanide binding was completely inhibited when Ba was added to the perfusate to block K channel-mediated K exit across the basolateral membrane.(ABSTRACT TRUNCATED AT 250 WORDS)
45 citations
TL;DR: The avidin-biotin peroxidase technique was used to determine the distribution of natriuretic peptides in the hearts and brains of the dogfish Qualus acanthias and the Atlantic hagfish Myxine glutinosa, and showed that a component of the natriUREtic peptide complement is similar to porcine brain natriurtic peptage or porcines C-type natriuredtic peptidase.
Abstract: The avidin-biotin peroxidase technique was used to determine the distribution of natriuretic peptides in the hearts and brains of the dogfishSqualus acanthias and the Atlantic hagfishMyxine glutinosa. Three antisera were used: one raised against porcine brain natriuretic peptide which cross-reacts with atrial natriuretic and C-type natriuretic peptides (termed natriuretic peptide-like immunoreactivity); the second raised against porcine brain natriuretic peptide which cross-reacts with C-type natriuretic peptide, but not with atrial natriuretic peptide (termed porcine brain natriuretic peptide-like immunoreactivity); and the third raised against rat atrial natriuretic peptide (termed rat atrial natriuretic peptide-like immunoreactivity). Only natriuretic peptide-like immunoreactivity was observed in the heart ofS. acanthias which was most likely due to the antiserum cross-reacting with C-type natriuretic peptide. No immunoreactivity was found in theM. glutinosa heart. In the brain ofS. acanthias, natriuretic peptide-like immunoreactive fibres were located in many areas of the telencephalon, diencephalon, mesencephalon, rhombencephalon, and spinal cord. Extensive immunoreactivity was observed in the hypothalamo-hypophyseal tract and the neurointermediate lobe of the hypophysis. Natriuretic peptide-like immunoreactive perikarya were found in ventromedial regions of the telencephalon and in the nucleus preopticus. Most perikarya had short, thick processes which extended toward the ventricle. Another group of perikarya was observed in the rhombencephalon. Porcine brain natriuretic peptide-like immunoreactive fibres were observed in the telencephalon, diencephalon, mesencephalon, and rhombencephalon, but perikarya were only present in the preoptic area. In theM. glutinosa brain, natriuretic peptide-like immunoreactive fibres were present in all regions. Immunoreactive perikarya were observed in the pallium, primordium hippocampi, pars ventralis thalami, pars dorsalis thalami, nucleus diffusus hypothalami, nucleus profundus, nucleus tuberculi posterioris, and nucleus ventralis tegmenti. Procine brain natriuretic peptide-like immunoreactive perikarya and fibres had a similar, but less abundant distribution than natriuretic peptide-like immunoreactive structures. Although the chemical structures of natriuretic peptides in the brains of dogfish and hagfish are unknown, these observations show that a component of the natriuretic peptide complement is similar to porcine brain natriuretic peptide or porcine C-type natriuretic peptide. The presence of natriuretic peptides in the brain suggest they could be important neuromodulators and/or neurotransmitters. Furthermore, there appears to be divergence in the structural forms of natriuretic peptides in the hearts and brains of dogfish and hagfish.
43 citations
TL;DR: The hypothesis that band 3 is involved in volume-activated taurine efflux is supported in the RBC of the two cyclostomes, hagfish and lamprey, which is reported to be deficient in band 3.
Abstract: Hypoosmotic stress in skate RBC causes cell swelling followed by the release of solutes (osmolytes) to bring about a regulatory volume decrease (RVD). The β-amino acid, taurine, is a primary osmolyte in RVD of skate RBC. Taurine efflux is inhibited by stilbene disulfonates and other inhibitors of the anion exchanger, band 3, suggesting that band 3 is involved in the release of taurine during RVD in skate RBC. Since RBC of the cyclostomes, hagfish and lamprey, are reported to be deficient in band 3, we examined taurine efflux, quantity of band 3, and volume response in these RBC. There was no significant increase in taurine efflux when hagfish RBC were exposed to hypoosmotic medium, and the rate of taurine efflux in these RBC was markedly lower than that in skate RBC. Hagfish RBC plasma membranes show only 11% of the level of 3H2DIDS bound to skate RBC membranes. In addition, DIDS-sensitive sulfate exchange is much lower in hagfish compared with skate RBC. Similarly, lamprey RBC showed little taurine efflux compared with skate, and the amount of 3H2DIDS binding to these RBC membranes was 24% that of skate. Finally, although both hagfish and lamprey RBC swell in hypoosmotic medium, the lamprey cells show an RVD while the hagfish cells do not. Thus, in the RBC of the two cyclostomes, one showing an RVD and the other not, low band 3 is associated with low volume-activated taurine efflux. These results support the hypothesis that band 3 is involved in volume-activated taurine efflux. © 1992 Wiley-Liss, Inc.
36 citations
TL;DR: Evidence is presented that granulosa cells secrete quantitatively important amounts of progesterone (P), testosterone (T), and estradiol-17 beta (E), while theca has a more limited capacity to synthesize T and E, which suggests a possible interaction betweengranulosa and theca for steroid biosynthesis.
Abstract: We investigated the steroid biosynthetic capabilities of ovarian granulosa and thecal elements of the viviparous dogfish, Squalus acanthias. In this report we present evidence that granulosa cells secrete quantitatively important amounts of progesterone (P), testosterone (T) and estradiol-17β (E), while theca has a more limited capacity to synthesize T and E. Ovarian granulosa cells were obtained from animals at each stage of gestation. After collagenase dispersion, an aliquot of 250,000 cells was incubated at 18°C in basal medium, containing Eagle's salts, glutamine, penicillin, streptomycin and adjusted with 136 mM sodium chloride and 350 mM urea. After a 4 hour incubation, the content of P, T, and E in medium was determined by radioimmunoassay. P was not detectable at any time, while E was present throughout the cycle, being maximal when gestation is three quarters complete (Stage C). T gradually increased from Stage B toward late pregnancy. In Stage C granulosa cells, E production increased in the presence of graded doses of T substrate. Also, a homologous pituitary extract (1/25 equivalents) and the calcium ionophore A23187 stimulated production of all 3 steroids. Using radioisotopes, granulosa cells showed a wide range of synthetic capacities. In Stage C thecal tissue, E production also increased in the presence of graded doses of T substrate, while pituitary extract only increased T. When granulosa and theca were recombined, in the presence of pituitary extract, P levels decreased with a corresponding increase in T, when compared to granulosa alone. These data suggest a possible interaction between granulosa and theca for steroid biosynthesis. They further indicate that granulosa cells alone have the capacity to synthesize P, T, and E, without any input from theca.
25 citations
TL;DR: Results suggest that the extension of microtubules through a tight contractile ring may be important for stabilizing that constriction and facilitating subsequent cytokinesis.
Abstract: During cytokinesis, a cortical contractile ring forms around a cell, constricts to a stable tight neck and terminates in separation of the daughter cells. At first cleavage, Ilyanassa obsoleta embryos form two contractile rings simultaneously. The cleavage furrow (CF), in the animal hemisphere between the spindle poles, constricts to a stable tight neck and separates the daughter cells. The third polar lobe constriction (PLC-3), in the vegetal hemisphere below the spindle, constricts to a transient tight neck, but then relaxes, allowing the polar lobe cytoplasm to merge with one daughter cell. Eggs exposed to taxol, a drug that stabilizes microtubules, before the CF or the PLC-3 develop, fail to form CFs, but form stabilized tight PLCs. Eggs exposed to taxol at the time of PLC-3 formation develop varied numbers of constriction rings in their animal hemispheres and one PLC in their vegetal hemisphere, none of which relax. Eggs exposed to taxol after PLC-3 initiation form stabilized tight CFs and PLCs. At maximum constriction, control embryos display immunolocalization of nonextractable alpha-tubulin in their CFs, but not in their PLCs, and reveal, via electron microscopy, many microtubules extending through their CFs, but not through their PLCs. Embryos which form stabilized tightly constricted CFs and PLCs in the presence of taxol display immunolocalization of nonextractable alpha-tubulin in both constrictions and show many polymerized microtubules extending through both CFs and PLCs. These results suggest that the extension of microtubules through a tight contractile ring may be important for stabilizing that constriction and facilitating subsequent cytokinesis.
17 citations
TL;DR: The absence of an effect of organic mercurials on chloride transport in the rectal gland suggests that its effect on another chloride transporting epithelia, the thick ascending limb of the loop of Henle, is not mediated by inhibition of the chloride cotransporter or Na+, K(+)-ATPase, common to both epithelial.
15 citations
TL;DR: When the Ca(2-)-sensitive fluorescent probe, Fura-2, or the Na(+)-sensitive probe, SBFI, in their cell permeable forms or the Cl(-)-specific probe, SPQ, were incubated with plasma membrane vesicles prepared from dogfish and bovine lenses fibers, there was a selective accumulation of the ion-specific probes within the vesicle.
13 citations
TL;DR: Metal uptakes by both species were biphasic, with rat cells accumulating more metal than the skate cells, and Hg accumulation was inhibited by Cu in both species, and increased by Cd only in the rat cells.
TL;DR: An antibody to the putative Chrysemys apolipoprotein B-100-like protein was developed and used in an ELISA to quantitate protein levels in plasma, suggesting its identity with apoledipopprotein B- 100.
Abstract: 1. 1. The isolation and purification of a putative apolipoprotein B-100 in the plasma of the freshwater turtle Chrysemys picta is described. 2. 2. The protein was purified through differential ultracentrifugation and subsequent Sepharose 6B column chromatography. 3. 3. The molecular weight of the protein determined by electrophoresis was approximately 350 kDa. 4. 4. An antibody to chicken apolipoprotein B-100 specifically recognizes this 350 kDa protein in Western blots, suggesting its identity with apolipoprotein B-100. 5. 5. An antibody to the putative Chrysemys apolipoprotein B-100-like protein was developed and used in an ELISA to quantitate protein levels in plasma. 6. 6. Acute estrogen treatment increased levels of apolipoprotein B-100 ( 7.64± 0.79 mg/ml plasma ) over that of control animals ( 5.07 ± 1.74 mg/ml plasma ). 7. 7. In contrast, chronic estrogen treatment reduced apolipoprotein B-100 significantly to 2.94 ± 0.53 mg/ml plasma ( P ).
TL;DR: Nickel, cadmium, and verapamil inhibited 3H-ACh release and evoked potential, indicating a block of pre-synaptic T Ca channels.
TL;DR: Together, the geometrical experiments strongly suggest that furrowing activity occurs in maximally affected areas, consistent with the equatorial contraction theory of cell division, but inconsistent with the aster relaxation theory.
Abstract: The division mechanism of animal cells is positioned by the mitotic apparatus. The mitotic apparatus determines the position by a pattern of regional inequality of its effect on the surface and cortex. Because the effect of the asters decreases with distance, the location of the division plane can be manipulated geometrically. It follows that cytokinesis should be preventable by imposition of a cell shape that prevents the normal pattern of unequal aster effect. The shape that inhibits division reveals something of the normal pattern of aster effect as well as the nature of the immediate response of the surface to the aster.
In 13 of 13 experiments, sand dollar (Echinarachnius parma) eggs fail to cleave when the polar and subpolar regions are extruded in the mitotic axis, although some surface contraction may develop in the extruded region. Extrusion was accomplished by sucking the appropriate regions into opposed pipets. A computer model of the relative aster effect in this circumstance indicates that the minimum is at the equator, and the maximum is in the extruded regions. These experiments indicate that furrows do not form where the aster effect is minimal. Previous experiments showed that cells divide when cells are artificially constricted in the equatorial plane where the aster effect is maximal. Together, the geometrical experiments strongly suggest that furrowing activity occurs in maximally affected areas. These results are consistent with the equatorial contraction theory of cell division, but inconsistent with the aster relaxation theory. © 1992 Wiley-Liss, Inc.