Showing papers on "Toad published in 1985"

Temperature-dependent calcium sensitivity changes in skinned muscle fibres of rat and toad.

Abstract: Single mechanically skinned muscle fibres of different types (fast- and slow-twitch mammalian; slow and twitch amphibian) were successively activated in solutions of various Ca2+ concentrations at different temperatures. An increase in temperature from 5 to 22 degrees C reversibly shifted the isometric steady-state force-pCa curves towards higher Ca2+ concentration for individual fibres of each of the muscle types. A further increase in temperature to 35 degrees C in mammalian fibres resulted in an additional decrease in Ca2+ sensitivity. The temperature dependence of Ca2+ sensitivity was greater in the 'faster' fibre types: fast-twitch greater than slow-twitch; twitch greater than slow. The maximum isometric force response, P0, of both rat and toad skinned fibres was found to be strongly dependent on temperature below 22 degrees C. No detectable force could be induced by Ca2+ in mammalian muscle fibres at 0-1 degree C while in toad fibres P0 decreased by about 90% when temperature dropped from 20 to 0 degree C. Since in mechanically skinned fibres of other amphibians (Bufo bufo, Rana species) P0 is only marginally affected it is likely that the P0-temperature relations are indicative of the range of temperature over which the muscles are normally functional. The P0-temperature relations of skinned muscle fibres closely resembled the P0-temperature relations of tetanically stimulated intact muscle preparations from the same species of animals suggesting that the contractile apparatus is mainly responsible for the variation of force response with temperature in intact muscle.

Receptor occupancy vs. induction of Na+-K+-ATPase and Na+ transport by aldosterone.

Abstract: In the urinary bladder of the toad Bufo marinus aldosterone (between 0.8 and 100 nM) stimulates Na+ transport [half-maximal induction concentration (K1/2) = 6.5 nM]. At low hormone concentrations (...

Inhibition of vasopressin-stimulated water flow in toad bladder by phorbol myristate acetate, dioctanoylglycerol, and RHC-80267. Evidence for modulation of action of vasopressin by protein kinase C.

Abstract: The action of vasopressin (AVP) in transporting epithelia is mediated by cyclic AMP(cAMP), whereas its effects in hepatocytes are mediated by calcium and phosphoinositides Based on our recent observation that AVP stimulates phosphoinositide turnover in toad bladder, we examined the role of calcium-phospholipid-dependent kinase (protein kinase C) as a modulator of AVP's hydroosmotic effect Phorbol myristate acetate (PMA), which can substitute for diglyceride as an activator of protein kinase C, the diglyceride dioctanoylglycerol, and RHC-80267, a glyceride lipase inhibitor that should increase diglyceride levels, inhibited AVP-stimulated water flow, but not water flow stimulated by cAMP, suggesting inhibition of cyclic AMP production Both the dioctanoylglycerol and RHC-80267, but not PMA, also decreased water flow in response to 8-bromo cAMP indicating a potential inhibition at post-cAMP events as well PMA increased prostaglandin synthesis; however, inhibition of water flow persisted even when prostaglandin synthesis was completely blocked by incubation with naproxen Furthermore, water flow was not inhibited by incubation with the inactive diglyceride substitute phorbol didecanoate, supporting the specificity of the PMA inhibition Consistent with the site of action at adenylate cyclase suggested by the transport experiments, PMA and RHC-80237 decreased both cell cAMP content and the cyclic AMP-dependent kinase ratio (-cAMP/+cAMP), an index of intracellular cyclic AMP effect Assay for protein kinase C activity in toad bladder epithelial cell supernatant demonstrated that the toad bladder indeed contains a kinase stimulable by phospholipid, calcium, and PMA As an apparently independent effect, we found that addition of PMA, but not dioctanoylglycerol or RHC-80267, to the mucosal bath increased both water permeability and the frequency of granular cell luminal membrane aggregates in the absence of vasopressin, consistent with stimulation of fusion events at the luminal membrane Our data suggest that protein kinase C can modulate AVP-stimulated water flow in toad bladder by inhibiting cAMP generation, and perhaps post-cAMP steps as well, and support the hypothesis that AVP-stimulated turnover of membrane phosphoinositides antagonize the effects of AVP via changes in diglyceride, calcium, and protein kinase C

Effects of internal and external pH on amiloride-blockable Na+ transport across toad urinary bladder vesicles.

Abstract: We have examined the effect of internal and external pH on Na+ transport across toad bladder membrane vesicles. Vesicles prepared and assayed with a recently modified procedure (Garty & Asher, 1985) exhibit large, rheogenic, amiloridesensitive fluxes. Of the total22Na uptake measured 0.5–2.0 min after introducing tracer, 80±4% (mean±se,n=9) is blocked by the diuretic with aK 1 of 2×10−8 m. Thus, this amiloridesensitive flux is mediated by the apical sodium-selective channels. Varying the internal (cytosolic) pH over the physiologic range 7.0–8.0 had no effect on sodium transport; this result suggests that variation of intracellular pHin vivo has no direct apical effect on modulating sodium uptake. On the other hand,22Na was directly and monotonically dependent on external pH. External acidification also reduced the amiloride-sensitive efflux across the walls of the vesicles. This inhibition of22Na efflux was noted at external Na+ concentrations of both 0.2 μm and 53mm. These results are different from those reported with whole toad bladder. A number of possible bases for these differences are considered and discussed. We suggest that the natriferic response induced by mucosal acidification of whole toad urinary bladder appears to operate indirectly through one or more factors, presumably cytosolic, present in whole cells and absent from the vesicles.

Interactions of vasopressin, cAMP, and prostaglandins in toad urinary bladder

Abstract: Prostaglandin (PG) inhibits the hydroosmotic effect of vasopressin We therefore reexamined the interaction of vasopressin (VP), cAMP, and prostaglandins in toad bladder epithelial cells Vasopressin slightly, but reproducibly, stimulated PGE2 and thromboxane B2 (TXB2) synthesis in cells prepared by the use of collagenase When cells were prepared in the presence of a readily reversible cyclooxygenase inhibitor, ibuprofen, subsequent PGE2 synthesis was enhanced sevenfold but that of TXB2 was not Increasing cAMP by either phosphodiesterase inhibition or 8-bromo-cAMP significantly inhibited both basal and VP-stimulated PGE2 synthesis This inhibition was overcome by addition of arachidonic acid Future studies employing these agents will have to consider these effects VP enhanced 32P labeling of phosphatidylinositol (PI) and phosphatidic acid This effect was prevented by the phosphodiesterase inhibitor, which also decreased phosphatidylcholine labeling The results indicate that the phosphodiesterase inhibitor for cAMP may decrease PG formation by interfering with phospholipase activation Furthermore, VP, similar to its effect in the liver, also increases PI turnover in toad bladder This may initiate PG synthesis and provide a link among VP, cAMP, and calcium A double-reciprocal feedback is proposed, whereby VP stimulates PG synthesis in a cAMP-independent manner and also inhibits PG synthesis in a cAMP-dependent manner

Prolactin binding sites in the brain and kidneys of the toad, Bufo arenarum Hensel.

Abstract: (125I)-ovine prolactin (oPRL) binding was found in several brain areas of the toad,Bufo arenarum Hensel. The olfactory bulb, cerebral hemispheres, and both dorsal and ventral mesencephalic regions showed saturable, high affinity, (125I)-oPRL binding, ranging between 5.6 to 29.9 fmol/mg protein, while the association constant (K a) by Scatchard analysis was between 4.0 to 8.7×109 M−1. This binding was compared with the Scatchard plot of the kidney, which has been already described by other groups, and gave 41.7 fmol/mg protein andK a 2.5×109 M−1. Liver showed no binding and in the cerebral hemispheres (125I)-oPRL was not displaced by non-lactogenic hormones, indicating that binding was hormone and tissue specific.

Specific binding sites for ovine prolactin in three amphibian cell lines

Abstract: Established cell lines (TB-6c and TB-M) obtained by continuous culture of epithelial cells from toad Bufo marinus urinary bladder, which, in culture, maintained a high degree of functional differentiation, exhibited a significant number of high-affinity (KA = 1-2 X 10(10) M-1) binding sites detected both with radioiodinated (125I) ovine prolactin (oPRL) and human growth hormone (hGH). Binding capacity was higher in the case of TB-6c cells (7,573 +/- 581 sites/cell) than with the TB-M cells (1,160 +/- 87). Similarly, binding sites for oPRL were characterized on Xenopus laevis kidney-derived cell line A6. With oPRL used both as tracer and standard, significant cross-reaction was observed with hGH, less with human or rat prolactin (PRL), and none with human chorionic somatomammotropin, bovine growth hormone, and rat luteinizing hormone or follicle-stimulating hormones. B. marinus pituitary extracts completely displaced the binding of 125I-oPRL to toad bladder binding sites. This finding of specific sites for PRL on amphibian bladder and kidney cells confirms that PRL exerts specific biological actions for the control of electrolyte and water metabolism in the amphibians.

Effect of hypobaric hypoxia on spermatogenesis, Leydig cells and delta 5-3 beta-hydroxysteroid dehydrogenase activity in toad.

Abstract: The effect of different grades of hypobaric hypoxia for 48 hours was studied on spermatogenesis, Leydig cells and delta 5-3 beta-hydroxysteroid dehydrogenase activity in toad (Bufo melanostictus). Maximum inhibition of testicular activity was noted in 7,315 m exposed animals. The impairment of testicular function at high altitude is possibly due to inhibition of gonadotrophin secretion.

Vasopressin-mediated protein phosphorylation in intact toad urinary bladder.

Abstract: Endogenous protein phosphorylation was examined in intact 32P-labeled toad bladders in response to arginine vasopressin (AVP) and other agents under conditions where the bladders were undergoing the normal hydroosmotic response. AVP increased 32P incorporation into proteins with apparent MW of 17,000, 28,000 and 34,000 and decreased 32P incorporation into a protein with MW 15,500. The cyclic AMP analog 8-(p-chloro-phenylthio)-cyclic AMP mimicked the effects of AVP on 32P incorporation. AVP-dependent changes in protein phosphorylation were found to be specific for the epithelium of the bladder and were blocked by the antagonist d(CH2)5-D-TyrVAVP. AVP caused increased phosphorylation even in the absence of an osmotic gradient, but the AVP-mediated decrease in 32P content of the 15,500 MW band was observed only in the presence of an osmotic gradient. Isolated epithelial cells also displayed AVP-stimulated increases in 32P incorporation into the MW 17,000 and 34,000 phosphoproteins, but no decrease in 32P incorporation into the 15,500-dalton band. Phosphorylation of the MW 34,000 band was maximal within 3 min. These data are consistent with the hypothesis that physiological effects of AVP may, in part, be mediated by cyclic AMP-dependent phosphorylation of specific proteins.

Effect of thyroxine on hepatic glucose-6-phosphatase activity and glycogen content of toad (Bufo melanostictus) and Lata fish (Ophicephalus punctatus) at different stages of life.

Abstract: The effects of thyroxine (T4) on hepatic glucose-6-phosphatase activity and glycogen content in toad (Bufo melanostictus) and Lata fish (Ophicephalus punctatus) were studied in order to show the difference, if any in the enzyme activity and glycogen metabolism in their liver. Thyroxine injections (1 microgram/g) for five consecutive days caused a reduction in hepatic glucose-6-phosphatase activity and glycogen content in toads of immature, juvenile and adult stages. In contrast, Lata fish of different stages showed an enhancement of hepatic glucose-6-phosphatase activity after T4 treatment (1 microgram/g, 5 injections). The liver glycogen content in Lata fish of different age groups was found to be reduced after T4 injections, but not so much as in the toad.

Presence of endogenous morphine in toad skin.

Abstract: Morphine was identified by immunological, pharmacological and physical criteria to be present in the skin of toad, rat and rabbit.

Studies on some enzymes of the toad (Bufo melanostictus) testis and their probable role at the time of fertilization

Abstract: Glycosidases like sialidase,β-galactosidase, α-L-fucosidase, N-acetyl hexosaminidase and proteases were detected in toad testis. Neuraminic acid aldolase activity was also detected. The enzyme activities were found to vary as production of spermatozoa varied. All enzymes, except N-acetyl glucosaminidase, were shown to decrease after injection of toad pituitary extract and they were also found to be absent from testis containing no spermatozoa. The glycosidases were found to act on toad oviduct jelly and they may therefore be involved in the degradation of the jelly after fertilization, into smaller bits, which may be utilized as nutrients by the fertilized zygote.

Effects of albumin on resting membrane potential of toad semitendinosus muscles

Abstract: I t has recent ly been shown by Macchia and colleagues (1981, 1982, 1984) and Page et a l . (1980), that the anion permeabi l i ty of toad semitendinosus muscles incubated in v i t r o in solut ions with a pH and e lec t ro ly te composTt-io-n--s-i-milar to that of toad plasma, is s i g n i f i c a n t l y greater than that of muscles in s i tu . When the bathing so lu t ion was toad plasma, or Ten the plasma protein albumin was added to the nonplasma incubation solut ion ( in physiological concentrat ions), the isolated muscles had s imi la r anion permeabi l i t ies as in s i tu muscles. This albumin e f fec t on anion perm-e-a~ty was found to be albumin concentration dependent and species spec i f i c . Only toad albumin made in v i t r o toad muscle behave l i ke muscles examined in s i t u . ~ i n e albumin proved to be the only nont-6-a~--~otein which could help in v i t r o toad muscles to re ta in t he i r anion permeabi l i t ies, although some anion permeabi l i ty changes were noted even with bovine albumin. Further, studies by Kernan (1960) and Page (1962) which demonstrated a hyperpolar iz ing ef fect of plasma on skeletal muscle membrane potent ia ls suggest that the permeabi l i ty of the ce l l membranes to sodium and or potassium may also be affected by the presence or absence of some plasma f rac t ion . To examine fu r ther the ef fects of plasma albumin on the permeab i l i t y character is t ics of skeletal muscle membrane, we examined the ef fects of toad plasma, and toad and bovine plasma albumin, on the rest ing membrane potent ia l , Em, of isolated toad semitendinosus muscles. Portions of th is work have previously been presented to the Biophysical Society (Shetty and Macchia, 1984). Semitendinosus muscles from the toad (Bufo marinus) were dissected out and placed in e i ther a ~ p a-Ta-sm-a or toad Ringer's with a pH and e lec t ro ly te ~omposition s imi la r to that of toad plasma (Danielson, 1964; Macchia et a l . , 1978; Macchia and Baumgarten, 1979). The composition of the Ringer's so lut ion (temperature 21-23 oc) was ( in mM/L): 73.0 NaCl; 4.7 KCI; 1.8 CaCl2; 0.56 MgCl2; 24.0 NaHC03; and 25.0 glucose. The pH of the incubation solut ions was set to 7.8 and the incubation solut ions were oxygenated with I00% 02 . The Plasma incubation solut ions were oxygenated By blowing oxygen over the surface of the so lu t ion. The pH of the incubation solut ions was measured at the beginning and the conclusion of the experiment. The incubation solut ion was continuously changed during the course of the experiment, by al lowing the so lu t ion to pass through the muscle incubation chamber from the solut ion reservo i r , by grav i ty f low. The experimental setup consisted of two solut ion reservoirs containing d i f f e ren t solut ions (control and test

Histochemistry of the juxtaglomerular apparatus in the toad Bufo bufo. Acid phosphatase activity of the epitheloid cells in the glomerular afferent arterioles.

Abstract: Histochemical techniques for acid phosphatase activity applied to kidney tissue of the toad Bufo bufo demonstrate that a high enzyme activity is present in the dense granules of the proximal tubule cells, but also in the media cells in the wall of the glomerular afferent arterioles. The acid phosphatase activity is confined to the characteristic granules in these juxtaglomerular cells, which therefore are lysosomal in nature.

The Anterior Preoptic Neurons of the Frog, Rana catesbeiana and Toad, Bufo bufo japonicus : Control of Mating Behavior

Abstract: Title The Anterior Preoptic Neurons of the Frog, Rana catesbeiana and Toad, Bufo bufo japonicus : Control of Mating Behavior Author(s) Urano, Akihisa Citation Current trends in comparative endocrinology : proceedings of the ninth International Symposium on Comparative Endocrinology, Hong Kong, 7-11 December 1981, eds. B. Lofts and W.N. Holmes, ISBN: 9622090397, pp. 1125-1126 Issue Date 1985 Doc URL http://hdl.handle.net/2115/43995 Type proceedings File Information CTCE_1125-1126.pdf

The effects of PGE2 on vasopressin--and guanine nucleotide-mediated adenylate cyclase activity in toad bladder membrane.

Abstract: PGE2 inhibited 10 m U/ml vasopressin-induced osmotic water flow of the toad bladder at 2 X 10(-8) M. PGE2 suppressed vasopressin-mediated cyclic AMP accumulation in epithelial cells and also vasopressin-mediated adenylate cyclase activity in a crude homogenate of the cells. However, PGE2 had no effect on cyclic AMP dependent and independent protein phosphorylation. These findings indicate that PGE2 inhibits vasopressin-induced water flow mainly through suppression of adenylate cyclase activity, and that the role of PGE2 at that point in the reaction leading to increased water permeability following cyclic AMP production may be slight. Under conditions in which the hormone and substrate are depleted, PGE2 and guanine nucleotides, such as GTP and Gpp(NH)p, additively bring about an increase in adenylate cyclase activity.

Physiological Mechanisms Underlying the Stimulation of Na Transport in the Toad Urinary Bladder by Aldosterone

Abstract: The amphibian urinary bladder, particularly that of the toad Bufo marinus, is a classical example of an aldosterone-responsive epithelium The early work of Crabbe (1961) established that this organ responded to physiological doses of the steroid in vitro as well as in vivo, thus opening up a large field of investigation of the mechanism of stimulation of Na transport by mineralocorticoids It soon became apparent that aldosterone works in much the same way as do the reproductive steroids The molecule combines with cytoplasmic receptors, and the active steroid-receptor complex is translocated to the nucleus where it stimulates the synthesis of specific mRNA species These are in turn translated into specific proteins, called aldosterone-induced proteins or AIP’s This scheme has been reviewed elsewhere (Feldman et al 1972;Edelman 1975) and will not be elaborated upon here