Detection of humpback whale (Megaptera novaeangliae) non-song vocalizations around the Vema Seamount, southeast Atlantic Ocean.

Humpback whales are a cosmopolitan, highly vocal species. Investigated here are their vocalizations recorded at the Vema Seamount (31°38'S, 08°20'E) from moored hydrophones in the austral spring of 2019. During the 11-d recording period over 600 non-song calls were detected. Calls were predominantly detected at night over three consecutive days. The most common calls were low, frequency-modulated sounds (whups). An impulsive sound (gunshot) previously unknown in humpback whales was also detected. The location and timing of the calls suggests that humpback whales may be using the Vema Seamount as a temporary stop on their migration to their polar feeding grounds.

Molecular and cellular physiology of the dissociation of atrial natriuretic peptide from guanylyl cyclase a receptors.

Guanylyl cyclase subtype A (GCA) is the main receptor that mediates the effects of atrial natriuretic peptide (ANP) in the regulation of plasma volume and blood pressure. The dynamics of the dissociation of ANP from GCA were investigated in cultured Chinese hamster ovary (CHO) cells stably transfected with wild-type (WT) or mutant GCA receptors. The rate of dissociation of specifically bound (125)I-ANP-(1-28) from intact CHOGCAWT cells at 37 degrees C was extremely rapid (K(off) = 0.49 +/- 0.02 min(-1)), whereas in isolated membranes prepared from these cells, the dissociation at 37 degrees C was >10-fold slower (K(off) = 0.035 +/- 0.006 min(-1)). The dissociation of ANP from CHOGCAWT cells showed remarkable temperature dependence. Between 22 and 37 degrees C, K(off) increased approximately 8 times, whereas between 4 and 22 degrees C, it increased only 1.5 times. Total deletion of the cytoplasmic domain or of the catalytic guanylyl cyclase sequence within this domain abolished ANP-induced increases in cGMP, dramatically slowed receptor-ligand dissociation by at least 10-fold, and abolished the temperature dependence of the dissociation of ANP. Deletion of the kinase-like domain led to maximal constitutive activation of guanylyl cyclase, markedly decreased K(off) to 0.064 +/- 0.006 min(-1), and also abolished the temperature dependence of dissociation. Substitution of Ser(506) by Ala and particularly the double substitution of Gly(505) and Ser(506) by Ala within the kinase-like domain markedly reduced ANP-induced increases in cGMP, whereas K(off) decreased modestly (albeit significantly) to 0.36 +/- 0.03 and 0.24 +/- 0.02 min(-1), respectively. As a whole, the results demonstrate for the first time that temperature per se or ATP alone cannot account for rapid GCA receptor-ligand dissociation under physiological conditions and suggest that ligand dissociation is modulated in part by the interaction of still unidentified cytosolic factors with the cytoplasmic domain of GCA.

Cloning of an unusual natriuretic peptide from the South American coral snake Micrurus corallinus

In the course of cloning abundant cDNAs from the South American coral snake Micrurus corallinus venom gland, we characterized a cDNA coding for a putative natriuretic peptide. All the natural natriuretic peptides described so far, possess a ring structure composed of 17 amino acids formed through an S-S bridge which is extended at the N-terminus by few to several amino acids and may be extended at the C-terminus, usually 4-7 amino acids. In contrast, the M. corallinus natriuretic peptide presents several distinct features: (a) the preform of the deduced natriuretic peptide displays an unusual C-terminus extension. This implies that the mature peptide has a long C-terminal tail or it is further extensively processed to result in the mature natriuretic peptide with the expected 4-7 amino-acid extension. (b) the deduced natriuretic peptide presents an unusual internal Cys within the ring structure. This raises the possibility of natriuretic peptides with a smaller ring structure. (c) the putative natriuretic peptide is flanked by two homologous peptides of unknown function. In addition, an analogous peptide was synthesized and assayed on perfused rat kidney, showing a dose-dependent response in urinary volume and sodium excretion. Moreover, northern-blot studies showed that M. corallinus natriuretic peptide transcripts were highly expressed in venom glands, but they were not detectable in other tissues like heart and brain, suggesting a main role for this M. corallinus natriuretic peptide in the venom gland or in the envenomation by this coral snake's bite

Cloning of an unusual natriuretic peptide from the South American coral snake Micrurus corallinus.

In the course of cloning abundant cDNAs from the South American coral snake Micrurus corallinus venom gland, we characterized a cDNA coding for a putative natriuretic peptide. All the natural natriuretic peptides described so far, possess a ring structure composed of 17 amino acids formed through an S-S bridge which is extended at the N-terminus by few to several amino acids and may be extended at the C-terminus, usually 4-7 amino acids. In contrast, the M. corallinus natriuretic peptide presents several distinct features: (a) the proform of the deduced natriuretic peptide displays an unusual C-terminus extension. This implies that the mature peptide has a long C-terminal tail or it is further extensively processed to result in the mature natriuretic peptide with the expected 4-7 amino-acid extension. (b) the deduced natriuretic peptide presents an unusual internal Cys within the ring structure. This raises the possibility of natriuretic peptides with a smaller ring structure. (c) the putative natriuretic peptide is flanked by two homologous peptides of unknown function. In addition, an analogous peptide was synthesized and assayed on perfused rat kidney, showing a dose-dependent response in urinary volume and sodium excretion. Moreover, northern-blot studies showed that M. corallinus natriuretic peptide transcripts were highly expressed in venom glands, but they were not detectable in other tissues like heart and brain, suggesting a main role for this M. corallinus natriuretic peptide in the venom gland or in the envenomation by this coral snake's bite.

Optimum lens aperture in phase-shifting speckle interferometric setups for maximum accuracy of phase measurement.

Negative exponentially distributed intensities of speckle fields seem unfavorable in terms of precision metrology, if interferometric setups are involved with a saturable photodetector and an analog-to-digital converter that imposes a finite resolution. By spatial integration, extended detector apertures modify the intensity distribution toward a less awkward function. However, because the detector aperture also integrates over points of rapidly changing speckle phases, this is done at the expense of a lower modulation of measured intensity during phase shift. An optimum set of parameters is calculated here, consisting of values for the lens aperture, the mean speckle intensity, and the beam ratio. The remaining phase-measurement error assumes its minimum of 10.6 mrad when the space-bandwidth product of the lens-detector system (thus concerning the lens aperture) is 0.31, the mean speckle intensity is 1/11 of the saturation intensity, and the reference intensity is four times higher than the mean speckle intensity. The 90 degrees phase-shift algorithms with either three, four, or five frames turned out to be quite powerful, even with interference signals of rather poor modulation. Not needing a very small lens aperture is interesting, because stopping down the lens is a trade-off with the limited power of the laser.

Role of atrial natriuretic factor in volume control.

Atrial natriuretic factor (ANF) is a 28 amino acid polypeptide hormone secreted mainly by the heart atria in response to atrial stretch. ANF acts on the kidney to increase sodium excretion and GFR, to antagonize renal vasoconstriction, and to inhibit renin secretion. In the cardiovascular system, ANF antagonizes vasoconstriction, and shifts fluid from the intravascular to the interstitial compartment. In the adrenal gland, ANF is a powerful inhibitor of aldosterone synthesis. ANF participates importantly in the natriuretic response to acute and chronic volume overload. ANF's property of shifting fluid from the vascular to the interstitial compartment acts as a buffering device, guarding against excessive plasma volume expansion in face of an increased total extracellular fluid volume. ANF is also a physiological modulator of GFR, and mediates nephron hyperfiltration and natriuresis when salt excretion is threatened by a reduction in the number of nephrons. Guanylyl cyclase (GCA) receptors mediate the effects of ANF by generating cGMP. Clearance receptors remove ANF from the circulation by receptor-mediated endocytosis, and serve as a hormone buffer system to impede large inappropriate fluctuations in plasma levels of ANF. The specific structure-function-dynamics relationships of these receptors serve to modulate the role of ANF in pressure-volume homeostasis.

Molecular determinants of the clearance function of type C receptors of natriuretic peptides.

Receptor-mediated endocytosis is the cellular mechanism by which type C receptors of natriuretic peptides exert their clearance function. In the present work, performed in recombinant Chinese hamster ovary cells stably transfected with wild type or mutated human kidney C receptors, we determined net endocytic rates (ER) of C receptor-ligand complexes, lysosomal hydrolysis of ligand (125I-labeled native atrial natriuretic factor, ANF1-28), and receptor recycling. Equilibrium ligand binding, immunocytochemistry, and immunoprecipitation were performed to characterize the transfected receptors. The net ER of recombinant wild type C receptors was approximately 6% of occupied receptors internalized per min, and C receptor-mediated lysosomal hydrolysis of ligand amounted to approximately 250% of specifically bound 125I-ANF1-28/h, with efficient recycling of internalized C receptors to the cell surface. Hypertonic sucrose reduced net ER and lysosomal hydrolysis of 125I-ANF1-28 more than 10-fold, indicating that endocytosis occurred via clathrin-coated pits. Total deletion of the cytoplasmic domain also reduced net ER and lysosomal hydrolysis of 125I-ANF1-28 by almost 10-fold, whereas deletion of the terminal 28 amino acids of the cytoplasmic tail led to a 4-fold reduction in these parameters. Replacement of cytoplasmic domain Tyr508 by Ala, or Tyr508 and Phe538 by Ala, reduced net endocytosis and lysosomal hydrolysis of 125I-ANF1-28 by 40-50%. Replacement of extracellular domain Cys473 by Ala impeded the constitutive formation of homodimers and reduced by approximately 50% the net ER and lysosomal hydrolysis of 125I-ANF1-28. These results demonstrate that the cytoplasmic domain of C receptors, Tyr508 within this domain, and constitutive receptor dimerization are the major molecular determinants of the clearance function of C receptors.

Camera influence on the phase-measurement accuracy of a phase-shifting speckle interferometer.

In a real phase-shifting interferometer the camera (i.e., a photodetector plus an analog-to-digital converter) cuts off intensities above some saturation level and provides a limited number of digitization steps. Owing to the intensity statistics of speckle fields, this might severely influence the accuracy of the calculated speckle phase. The optimum beam ratio and the modulation of the camera are computed. To calculate the standard deviation of the phase difference, first, we derive a relation that shows that the variances of the two measured phase frames are equal and that they must be added with the decorrelation-dependent variance. To obtain the minimum phase-measurement error of 25.1 mrad, it is found that the mean speckle intensity ought to be adjusted to be 0.058 times the saturation intensity of the camera and that the beam ratio is to be 5.7. The results are confirmed by computer simulation of a two-wavelength speckle interferometer.

Conversion of T-kinin to bradykinin by the rat kidney.

Isolated rat kidneys were perfused with T-kinin (TK, Ile-Ser-BK) and bradykinin (BK). HPLC analysis of perfusate samples taken at 2-10 min during the TK perfusion (0.5 nmol/mL initial concentration) showed two peptide peaks, the first one eluting at 14.42 min, the same retention time for standard BK, and the second at 16.20 min, corresponding to that of TK. When BK (0.5 nmol/mL) was perfused, only its corresponding peak was obtained although total BK recovery was reduced quickly, as expected. Using both HPLC analysis and a kinin bioassay on the isolated guinea pig ileum, it was found that 12% of the added TK was converted to BK during the first perfusion cycle (2 min). While the BK recovered (12-14% from the initial TK concentration) was maintained at a similar proportion between the 2nd and the 10th min of perfusion, the rate of TK disappearance, as well as its full recovery from the perfusate, indicated further fragmentation of peptides during kinin perfusion. In the presence of 5 microM DL-mercaptomethyl-3-guanidino-ethylthiopropanoic acid (Mergetpa), an inhibitor of plasma carboxypeptidase N (EC 3.4.17.3), the rate of conversion of TK to BK was not affected. On the other hand, the kinase II inhibitor bradykinin potentiating peptide 9a (BPP9a) increased both the proportion of TK converted to BK and the disappearance rate of TK from the perfusate. In the presence of BPP9a, the rate of BK production increased from 1.5 +/- 0.2 to 7.6 +/- 0.9 nmol/min. Furthermore, the recovery of BK was reduced during the first 2 min of perfusion to 7.6% and the conversion rate to 0.9 nmol/min when TK was perfused into the kidney in the presence of 10 microM bestatin, a known inhibitor of aminopeptidases. These data indicate that in the kidney TK is converted to BK, probably by aminopeptidase M, thus suggesting that BK is, in fact, an additional and functional kinin, inducing physiological and/or pathophysiological effects in the rat kidney in which TK is the main kinin released.

Clearance receptor and neutral endopeptidase-mediated metabolism of atrial natriuretic factor.

A novel small linear C-atrial natriuretic factor receptor ligand [C-ANF-(11-15)] and phosphoramidon (PHO) were used to determine the effects of C-ANF receptor blockade alone, or in combination with inhibition of neutral endopeptidase (NEP), on the pharmacokinetics and metabolism of ANF in the rat. C-ANF-(11-15) infusion decreased apparent volume of distribution (Vss) and metabolic clearance rate (MCR) of administered 125I-ANF-(1-28) to one-third of their control values, whereas PHO alone was without effect on these parameters. In combination with C-ANF-(11-15), however, PHO further decreased MCR of 125I-ANF-(1-28) and increased plasma half time by more than threefold. High-performance liquid chromatography analysis revealed that C-ANF-(11-15) inhibited the delayed appearance of free 125I and [125I]monoiodotyrosine but had no effect on the small proportion of NEP metabolites in plasma. The combination of C-ANF-(11-15) and PHO further delayed the appearance of small metabolites, abolished the appearance of NEP metabolites, and markedly prolonged the permanence of intact 125I-ANF-(1-28) in plasma. The results demonstrate that C-ANF receptor blockade by C-ANF-(11-15) impairs clearance and metabolism of ANF, an effect which is synergistically potentiated by concomitant inhibition of NEP. C-ANF-(11-15) alone or in combination with NEP inhibitors may be a potentially useful therapeutic tool in the treatment of cardiovascular and renal diseases.

Renal receptors and effects of atrial natriuretic factor in compensatory renal hypertrophy.

In the present study we investigated the in vivo and in vitro renal responsiveness to ANF, and the adaptation of ANF receptors in compensatory renal hypertrophy in the rat. One week after left nephrectomy (UNx), plasma levels of immunoreactive ANF, blood pressure (MAP), hematocrit (Hct), and urine flow rate (V) were unaltered compared to control (C) rats. Baseline GFR and potassium excretion (UKV) were significantly higher, and sodium excretion (UNaV) tended to be elevated in UNx rats. Administered ANF led to similar dose-related decreases in MAP and increases in Hct in UNx and C rats. However, at each dose of infused ANF, absolute values and the increase in GFR and UNaV were higher in UNx than in C rats. Hypertrophied (H) kidneys were removed from UNx and perfused in vitro to determine distribution and density of ANF receptors, responsiveness to ANF, and receptor-mediated organ clearance of 125I-ANF1-28. The density of ANF receptors in cortex, outer medulla, and papilla of H kidneys was not significantly different from that in C kidneys. In H isolated kidneys, ANF led to dose-related increases in GFR, V, UNaV, and UKV that were indistinguishable (P greater than 0.05) from those in C kidneys. Receptor-mediated organ clearance of 125I-ANF1-28 in isolated H kidneys was 2.8 +/- .02 ml/min, a value not significantly different (P greater than 0.05) from that in C kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamics of atrial natriuretic factor-guanylate cyclase receptors and receptor-ligand complexes in cultured glomerular mesangial and renomedullary interstitial cells.

The dynamics of the guanylate cyclase receptor of atrial natriuretic factor (GCA-ANF receptor) were investigated in cultured glomerular mesangial and renomedullary interstitial cells from the rat. In these cells, the GCA-ANF receptor did not mediate internalization and lysosomal hydrolysis of 125I-ANF1-28 and did not undergo ligand-induced endocytosis. Glomerular mesangial cells were able, however, to mediate internalization and lysosomal hydrolysis of 125I-ANF1-28 via clearance ANF (C-ANF) receptors and to promote rapid receptor-mediated internalization and lysosomal hydrolysis of 125I-(Sar1) angiotensin II. Radioligand specifically bound to surface GCA-ANF receptors was rapidly dissociated at 37 degrees C (k(off) greater than 0.8 min-1), with a Q10(30-37 degrees C) greater than 6. The dissociation was markedly slower at subphysiological temperatures (Q10(4-30 degrees C), 2-3) or in the presence of 0.5 mM amiloride. The results demonstrate that the GCA-ANF receptor, contrary to C-ANF receptors and most other polypeptide hormone receptors, is a membrane resident protein that does not mediate internalization and lysosomal hydrolysis of ligand. The termination of the interaction of ANF with GCA-ANF receptors results from a physiological process that leads to rapid dissociation of receptor-ligand complexes. The unique dynamics of GCA-ANF receptor-ligand complexes are likely to contribute importantly to stimulus-response homeostasis of ANF.

Effects of small C-ANF receptor ligands on plasma levels of atrial natriuretic factor, blood pressure, and renal function in the rat.

In this article, after a very brief review on ANF receptors, we report our study on the effects of small C-ANF receptor ligands in the rat. Two small ligands were synthesized: 2-naphthoxyacetyl-isonipecotyl-rANF11-15-NH2 (5 aa), containing 5 amino acids; and Ala7-rANF8-17-NH2 (10 aa), containing 10 amino acids from the ring structure of ANF1-28. After control periods, 5 aa or 10 aa were infused i.v. at a dose of 10 micrograms.min-1.kg-1 body weight for 70 min in anesthetized rats, followed by a 60-min recovery period. The 5 aa and 10 aa peptides significantly and reversibly increased plasma levels of endogenous immunoreactive ANF by 106 +/- 29 and 52 +/- 24 pg/mL, respectively. Infusion of the 5 aa peptide significantly decreased mean arterial blood pressure from 113 +/- 1 to 100 +/- 3 mmHg (1 mmHg = 133.32 Pa) and increased glomerular filtration rate from 1.6 +/- 0.2 to 2.3 +/- 0.2 mL/min, sodium excretion from 0.6 +/- 0.3 to 3.4 +/- 0.4 mumol/min, and potassium excretion from 0.5 +/- 0.2 to 1.2 +/- 0.2 mumol/min. Similar results were obtained with the 10 aa peptide. The effects of both peptides on blood pressure and sodium excretion persisted throughout the recovery period. The results confirm and extend previous observations showing that C-ANF receptors mediate the removal of ANF from the circulation. The shortening of the minimal peptide length necessary to bind to C-ANF receptors markedly enhances the possibility of developing orally active C-ANF receptor ligands for the treatment of cardiovascular and renal diseases.

DuP 753 is a potent nonpeptide antagonist of angiotensin II receptors in isolated perfused rat kidney and cultured renal cells.

In the present study we investigated the antagonist action of DuP 753 (2-n-butyl-4-chloro-5-hydroxy-methyl-1-[2'-(1H-tetrazol-5-yl)biphe nyl-4-yl) methyl]imidazole, potassium salt) on angiotensin II (AII) binding and vascular effects in the isolated perfused rat kidney. In addition, we determined binding of DuP 753 in cultured glomerular mesangial cells and renomedullary interstitial cells. In the isolated kidney, DuP 753 fully displaced AII from its specific binding sites with high affinity (IC50 = 200 nmol/L) and antagonized the vasoconstrictive effect of AII in a dose-related manner with an ED50 of 170 nmol/L. These effects of DuP 753 were qualitatively similar to those of saralasin and the antagonist effect of DuP 753 on AII-induced renal vasoconstriction was fully overcome by excess AII. DuP 753 had no effect on its own on renal vascular resistance. In cultured glomerular mesangial cells and renomedullary interstitial cells, DuP 753 fully inhibited the specific binding of [125I]-Sar-AII at 1 mumol/L with IC50s of 6.7 and 11 nmol/L for glomerular mesangial cells and renomedullary interstitial cells, respectively. The present results demonstrate that a novel imidazole derivative, DuP 753, is a powerful non-peptide antagonist of angiotensin II receptors in isolated perfused rat kidney and in cultured glomerular mesangial and renomedullary interstitial cells.