Showing papers on "Toad published in 1992"

Control of adipose tissue lipolysis in ectotherm vertebrates

Abstract: Lipolytic activity of fish (Hoplias malabaricus), toad (Bufo paracnemis), and snake (Philodryas patagoniensis) adipose tissue was investigated in vivo and in vitro. Catecholamines or glucagon did not affect the release of free fatty acids (FFA) by incubated fish and toad adipose tissue. Catecholamines also failed to activate snake adipose tissue lipolysis, which even decreased in the presence of epinephrine. However, glucagon stimulated both the lipolytic activity of reptilian tissue in vitro and the mobilization of FFA to plasma when administered to snakes in vivo. The release of FFA from incubated fish, amphibian, and reptilian adipose tissue increased markedly in the presence of cAMP or xanthine derivatives, inhibitors of phosphodiesterase. Forskolin or fluoride, activators of specific components of the adenylate cyclase system, strongly stimulated toad adipose tissue lipolysis. The data suggest that adipocyte triacylglycerol lipase of ectotherm vertebrates is activated by a cAMP-mediated phosphorylation and that the organization of the membrane-bound adenylate cyclase system is similar to that of mammals.

Effect of exogenously applied polyamines on malathion toxicity in the toad Bufo arenarum Hensel.

Abstract: The polyamines putrescine, spermidine, and spermine, are able to potentiate the toxicity of malathion in Bufo arenarum Hensel toad larvae. This action is synergistic and maximal with spermidine, which elevated up to 13-fold the mortality produced by this organophosphorus compound. Spermidine increased the degree of inhibition of acetylcholinesterase activity elicited by malathion, and impaired the recovery of this activity at the end of the treatment. Spermidine had no effect on the enzyme when applied alone. Toxic effects were also observed with the polyamines themselves when applied at concentrations similar to the intracellular levels described for rapid-growing organisms.

The β Subunit Modulates Potassium Activation of the Na‐K Pumpa

Abstract: We recently cloned the alpha 1 and the beta 1 and beta 3 subunits of the Na,K-ATPase of the toad Bufo marinus. To investigate possible functional differences between beta 1 and beta 3, we studied the potassium activation of Na-K pumps expressed in the oocyte of Xenopus laevis. Na-K pump activity was measured as K(+)-induced current in voltage-clamped oocytes. We could take advantage of the relative resistance to ouabain conferred by the Bufo alpha subunit to study specifically the exogenously expressed Na-K pumps after inhibition of the ouabain-sensitive endogenous Xenopus Na-K pumps. Coinjection of Bufo alpha 1 subunit cRNA with either beta 1 or beta 3 cRNAs results in the expression of functional Na-K pumps that share similar low ouabain sensitivity but differ in their K+ half activation constant (K1/2). Similar results were obtained with Xenopus alpha 1 and beta 1 or beta 3 subunits and with Bufo/Xenopus heterodimers. We conclude that some specific sequence of the beta subunit can influence the activation of the Na,K pump by extracellular K+ ions.

Differentiation of endocrine myocardiocytes in the developing heart of the toad (Bufo arenarum Hensel).

Abstract: The differentiation of endocrine myocardiocytes was investigated in the heart of developing toad Bufo arenarum Hensel, combining ultrastructural and immunocytochemical procedures. The distribution of immuno-reactive atrial natriuretic peptide (ANP) in the whole heart was appraised by light microscopy, applying biotin-streptavidin and immunofluorescence techniques. With the latter procedures ANP was first recognized at embryonic stage 22, in both atrium and ventricle. In the ensuing stages the ANP-reactivity became stronger in the atrium, while it became dimmer in the ventricle. At the end of the larval prometamorphic stage, atrial myocardiocytes acquired almost all the features of adult myoendocrine cells. At electron microscope level, small inclusions, about 110-120 nm in diameter, resembling secretory granules were found in myoendocrine cells beginning at embryonic stage 22. However, no immunogold labeling of ANP occurred until stage 25. The number of secretory granules diminished in the ventricles and increased in the atrium of the larval heart and at the end of the prometamorphic stage the atrial myoendocrine cells presented the ultrastructural characteristics of active secretory cells. The synthesis of ANP in larvae is enhanced at a critical period of development when the developing toad switches from an aquatic environment to terrestrial life. The cardiac hormones seem to play a key role in the regulation of the osmolarity of body fluids at this developmental stage.

Urinary Ca2+ and the regulation of K+ secretion in toad bladder by neurohypophyseal hormones.

Abstract: We measured net K+ fluxes in the isolated toad urinary bladder to determine whether neurohypophyseal hormones control K+ secretion in this tissue. To determine if the pathway involved in K+ secretion is similar to a Ca2+-blockable alkali cation channel in the apical membrane of toad bladder, previously described in electrophysiological studies, we measured K+ fluxes in either the presence or absence of Ca2+ in the mucosal bathing solution. Oxytocin enhanced K+ secretion in both cases; however, the enhancement was markedly greater in the absence of mucosal Ca2+. In other experiments the transepithelial voltage was held constant at a value of 120 mV (mucosa negative) to find whether hyperpolarization would enhance K+ secretion to the levels seen in Ca2+-free solutions. The response to oxytocin was markedly greater in the absence of mucosal Ca2+ even when the transepithelial voltage was continuously hyperpolarized. These observations suggest that the properties of the activated pathway are akin to those of the previously described Ca2+-blockable alkali cation channel. We also found that toad bladder urine often contained extremely low levels of Ca2+; therefore neurohypophyseal hormonal control of K+ transport across the bladder may play an important role in amphibian K+ balance.

Serous cutaneous glands of the western spade-foot toad Pelobates cultripes (Amphibia, Anura): an ultrastructural study on adults and juveniles.

Abstract: The venom glands of the western spade-foot toad Pelobates cultripes were studied under light and electron microscopes. The glands exhibit the structural patterns usual in anurans, including the typical secretory syncytium. The peripheral cytoplasm contains a single row of nuclei and secretory organelles related to proteosynthesis. The inner cytoplasm is filled with large vesicles holding a thin product which originates from the merging of smaller ones containing a thicker material derived from the Golgi apparatus. The appearance and maturation of P. cultripes venom have been compared with patterns of biosynthesis and secretory evolution described in serous cutaneous glands of several anuran species. Following these criteria, the traditional trends in the terminology and classification of serous glands in anuran skin are discussed and reviewed.

Caffeine effects on heart muscle energetics: species differences.

Abstract: The effects of caffeine (1mM) on energy expenditure and mechanical parameters in rat and toad perfused heart ventricles were examined at various stimulation frequencies. While in rat muscles caffeine significantly depressed developed tension and maximal rates of contraction and relaxation at all frequencies tested, in toad ventricle a slight positive inotropic effect was observed. Even though caffeine did not alter total contraction time in both preparations, in the rat ventricle the last part of relaxation was prolonged. In rat ventricle in the presence of caffeine, the ratios between active heat production per beat and either developed tension or tension time integral increased at all frequencies tested (+303 +/- 47 microJ.mN-1 x g-1 and +1.21 +/- 0.13 mJ.mN-1 x s-1 x g-1 respectively) indicating a decrease in contractile economy. In toad ventricle no changes on these ratios were observed. The fact that only in rat ventricle caffeine decreased muscle economy suggests that caffeine affects a system that is active in rat ventricle but it is not operative in toad ventricle. This gives support to the hypothesis that if in rat ventricle SR-Ca pump (1 ATP hydrolyzed/2 Ca transported) is inhibited by caffeine cytosolic Ca would have to be removed by alternative mechanisms such as Na-Ca exchanger or sarcolemmal Ca pump both with a higher rate of ATP hydrolysis (1 ATP hydrolyzed/Ca transported) with the consequent decrease in muscle economy. Resting heat production was increased by caffeine in both preparations and the magnitude of the increment (+3.0 +/- 0.6 mW.g-1 and +0.75 +/- 0.21 mW.g-1 for rat and toad ventricle respectively) also correlates with the different degree of SR activity in both species.

The generation and changing retinal distribution of displaced amacrine cells in Bufo marinus from metamorphosis to adult.

Abstract: The generation and retinal distribution of displaced amacrine cells (DAs) were studied from metamorphosis to adult in the cane toad Bufo marinus. Displaced amacrine cells were identified by inducing chromatolytic changes in ganglion cells (GCs) following optic nerve section. Cells that did not chromatolyse in the ganglion cell layer (GCL) of the retina were regarded as DAs. The number of DAs increased considerably from an estimated 10000 at metamorphosis to 211000 in the adult toad, and was accompanied by a substantial decrease of average cell density. In contrast to the reported 6:1 cell density gradient of all cells of the GCL in adult toad (Nguyen and Straznicky 1989) only a shallow 1.6:1 density gradient of DAs from the visual streak to the dorsal and ventral retinal margins was detected. Consequently, the incidence of DAs increased from 15% of all cells of the GCL in the visual streak to 30% in the dorsal and ventral peripheral retina. These results indicate that the ratio of the newly generated DAs and GCs at the ciliary margin must be changing during development. More GCs are generated before and around metamorphosis then DAs, in contrast to the relative increase of the percentage of DAs generated after metamorphosis. The possible control of the numbers of DAs in the GCL is discussed.

Comparative effects of mast cell degranulators on perfused systemic blood vessels of Bufo melanostictus and Rana tigrina.

Abstract: Three agents known to induce release of mast cell constituents, viz. polymyxin, compound 48/80 and polysorbate-80, were evaluated for effect on perfused blood vessels of R. tigrina and B. melanostictus. The mast cell degranulators caused vasoconstriction in frog and toad, except that for P-80 whose responses in toad were equivocal. Toads showed a general low responsiveness in comparison to frogs. Pharmacologic intervention with pheniramine, metergoline, hydergine, atropine and mecamylamine, respectively ruled out role of histamine, 5-HT, catecholamine or acetylcholine or even autonomic mechanisms in the above phenomena. The observations are suggestive of phylogenetic differences in biochemical profile of mast cells in amphibian species.

[A voltage-dependent potassium channel of outward rectifier type in plasma membrane of oocyte from toad, Bufo bufo gargarizans].

Abstract: Membrane properties of the fully-grown oocytes from toad, Bufo bufo gargarizans, were studied by using voltage-clamp technique. It was found that a sustained outward current was elicited by membrane depolarization to -30 mV or more positive value. The increase of the current was nearly proportional to the degree of depolarization. The peak value of the current ranged 2-5 microA at a membrane potential of 20 mV in oocytes from different toads. The current was inhibited by antagonists of potassium channel, TEA and 4-AP. The concentration of TEA capable of inhibiting half of the current was 2.6 mmol/L. Chloride channel antagonist 9-AC (2.5 mmol/L) had no effect on the current. Triple the extracellular calcium concentration did not show any effect either. The reversal potential of the current varied with an increase of 47.3 mV per decade change of the extracellular potassium concentration. Changing extracellular concentration of sodium or chloride did not shift the reversal potential. It was concluded that the outward current was a voltage-activated potassium current. The voltage-dependent potassium current decreased after treatment of the oocytes with progesterone to a state of maturation. A large decrease of the current (to about 1/20 of the control) occurred to the oocytes obtained from hibernating toads while a less striking decrease of the current (to about 1/3 of the control) was observed in the oocytes from toads all year round reared at 25-30 degrees C.

Sexual development of immunocompetence in the toad, Bufo regularis

Abstract: The kinetics of primary anti-rat erythrocytes (RRBC) antibdody were compared in juvenile and adult toads Bufo regularis. The antibody titers were measured by haemagglutination assay, and antigen specific rosette-forming cells were enumerated in the spleen using immunocytoadherence assay. Both adults and juveniles responded to RRBC, with adult being always the highest responder. Among the adult toads, slight differences between male and female could be observed. However, juvenile toads did not demonstrate sexassociated immune differences.

Studies on the physiological function of spermine in the process of progesterone induced toad oocyte maturation

Abstract: Spermidine or spermine but not putrescine inhibited progesterone induced Bufo bufo gargarizans oocyte maturation. The ID50 for spermine inhibition via intra - oocyte microinjection on maturation induced by progesterone was 6. 8 mM(100 nl). Spermine could inhibit MPF induced toad oocyte maturation with a much higher ID50. A 55 kD protein was dephosphorylated during the process of progesterone induced oocyte maturation. Spermine selectively promoted the level of phosphorylation, of this protein in both progesterone- stimulated and hormone- untreated oocytes. The extent of its dephosphorylation was fairly correlated with the percentage of GVBD in the hormone stimulated oocytes. The level of endogenous spermine was reduced by 28% between the period of 0. 40 GVBD50 and 0. 60 GVBD50, at which 55 kD protein was dephosphorylated. Spermine inhibited progesterone- stimulated protein synthesis in almost the same dose dependent manner as its inhibitory effect on the hormone- induced maturation. The endogenous spermine regulated 55 kD protein dephosphorylation which may trigger the increase of protein synthesis and in turn promote the activation of MPF. It is possible that 55 kD protein may be one of the components of messenger ribonucleoprotein (mRNP) particles.

A voltage-dependent potassium channel of outward rectifier type in plasma membrane of oocyte from toad, bufo bufo gargarizans

Abstract: Membrane properties of the fully-grown oocytcs from toad, Bufo bufo gar-garizans, were studied by using voltage-clamp technique It was found that asustained outward cuttrnt was elicited by membrane depolarization to--30 mVor more positive value The increase of the current was nearly proportional tothe degree of depolarization The peak value of the current ranged 2--5 μA ata membrane potential of 20 mV in oocytes from different toads The currentwas inhibited by antagonists of potassium channel, TEA and 4--AP The con-centration of TEA capable of inhibiting half of the current was 26 mmol/L Chlo-ride channel antagonist 9--AC (25 mmol/L) had no effect on the current Triplethe extracellular calcium concentration did not show any effect either The re-versal potential of the current varied with an increase of 473mV per decade changeof the extracellular potassium concentration Changing extracellular concen-tration of sodium or chloride did not shift the revelsal potential It was concludedthat the outward current was a voltage-activated potassium current The voltage-dependent potassium current decreased after treatment of the oocytes with proges-terone to a state of maturation A large decrease of the current (to about 1/20 ofthe control) occurred to the oocytes obtained from hibernating toads while a lessstriking decrease of the current (to about 1/3 of the control) was observed in theoocytes from toads all year round reared at 25--30℃