Showing papers on "Toad published in 1980"

Mechanism of action of aldosterone on active sodium transport across toad skin.

Abstract: Epithelium of the abdominal skin of the toad,Bufo marinus, has been studied by microelectrode impalement. Using an electrical equivalent circuit model, effective EMF's and specific conductances of the apical and basolateral membrane could be calculated. The skin was divided into 2 fragments for incubation in the presence, or not, of aldosterone (≥0.1 μM). After incubation overnight, sodium transport by the hormone-treated piece was increased 2.7-fold on average, compared to the untreated control. Concomitantly, conductance of the apical border increased more than 3-fold. Furthermore, mean conductance and electromotive force at the basolateral border increased by 80% and by 10%, respectively. Whether the latter changes merely represent delayed adaptation to increased apical conductance, cannot be settled from the data available.

Effect of verapamil on the hydroosmotic response to antidiuretic hormone in toad urinary bladder.

Abstract: To investigate the role of the calcium ion in the hydroosmotic response to antidiuretic hormone (ADH), the effects of verapamil, an inhibitor of calcium ion entry into cells, on stimulated water flow was examined in vitro in the toad urinary bladder. Verapamil, 50 micro M, decreased ADH-stimulated osmotic water flow from 23.4 +/- 4.1 to 9.9 +/- 3.3 mg . min-1 . hemibladder-1 (mean +/- SE, n = 12, P < 0.001). That this inhibitory effect was due to a verapamil-induced alteration in cellular calcium metabolism is suggested by the findings that 45Ca2+ uptake by isolated toad bladder epithelial cells was reduced nearly 50% in the presence of verapamil and that reversibility of verapamil's inhibitory action was calcium dependent. Additionally, verapamil reduced theophylline- (20 mM) stimulated water flow from 22.8 +/- 2.7 to 9.5 +/- 2.9 mg . min-1 . hemibladder-1 (n = 7, P < 0.001) but enhanced cAMP- (10 mM) induced water flow from 12.8 +/- 2.5 to 21.6 +/- 1.1 ng . min-1 . hemibladder-1 (n = 7, P < 0.001). The latter effect was due, at least in part, to a direct inhibitory effect by verapamil on phosphodiesterase activity of toad bladder homogenates. These results, therefore, suggest that the calcium ion is an important coupling factor at the level of the adenylate cyclase enzyme complex for the stimulus-reabsorption coupling between ADH and the transporting epithelia of the toad urinary bladder.

Glyoxylate cycle in toad urinary bladder: possible stimulation by aldosterone.

Abstract: A homogenate of the toad urinary bladder epithelial cell layer has the two enzymatic activities unique to the glyoxylate cycle--isocitrate lyase (threo-Ds-isocitrate glyoxylate-lyase, EC 4.1.3.1) and malate synthase [L-malate glyoxylate-lyase (CA-acetylating), EC 4.1.3.2]--as well as the capacity to carry out CN-insensitive palmitoyl-CoA oxidation. When tissue is incubated in the presence of a fatty acid substrate, tissue glycogen levels increase. Additionally, in the presence of aldosterone, glycogen levels are higher. These data demonstrate the presence of glyoxylate cycle enzymes in tissue of a higher animal and raise the possibility that such tissue can convert lipid to carbohydrate.

Somatostatin: occurrence in urinary bladder epithelium and renal tubules of the toad, Bufo marinus

Abstract: Immunohistochemical techniques were used to detect immunoreactive somatostatin-like material in toad urinary bladder epithelium and in kidney distal tubules and collecting ducts. This material has immunological and chromatographic properties identical to those of synthetic cyclic somatostatin. The occurrence of somatostatin-like material in antidiuretic hormone-sensitive portions of the renal urinary system suggests a local regulatory or paracrine role for somatostatin.

Ultrastructure of the renal juxtaglomerular complex and peripolar cells in the axolotl (Ambystoma mexicanum) and toad (Bufo marinus).

Abstract: Renal juxtaglomerular regions were examined in the axolotl (Ambystoma mexicanum and toad (Bufo marinus). Prominent granulated peripolar epithelial cells were found surrounding the origin of the glomerular tuft in the axolotl. These cells resembled the peripolar cells recently discovered in mammalian species. They contained multiple electron-dense cytoplasmic granules, some of which showed a paracrystalline substructure and signs of exocytoxic activity. Such cells were difficult to find and smaller in the toad. In contrast, granulated juxtaglomerular arteriolar myoephithelial cells were much more readily found and larger in the toad than in the axolotl. No consistent differences were noted in juxtaglomerular cells or their granules in response to changes in environmental chloride concentration.

The Three-Dimensional World of a Toad

Abstract: The path chosen by a toad (Bufo viridis) was examined when a barrier was placed between it and its food. The toad plans its route before it sets out, and so its route reveals something of its perceptions of its immediate environment. If there is a gap in the barrier wider than 3 cm (the width of the toad's head), the toad aims for the gap, if not, it detours round the end of the barrier. Provided that the toad starts no further than 20 cm from the fence, its choice between detour and direct approach is governed by the physical size of the gap and not by the angle that the gap subtends on the retina, indicating that the toad has size constancy. Similarly, it is less likely to detour round wide barriers than narrow ones and again its behaviour is controlled by the real width of the barrier and not by the retinal subtense.

Somatostatin: an endogenous peptide in the toad urinary bladder inhibits vasopressin-stimulated water flow

Abstract: Somatostatin (somatotropin release-inhibiting factor; SRIF) is a tetradecapeptide present in brain, pancreas, gastrointestinal tract, and thyroid that inhibits the secretion or action of several hormones in these tissues. We observed that the toad urinary bladder contains concentrations of endogenous somatostatin (8.0 pg/micrograms of protein) comparable to those found in the mammalian pancreas and gastrointestinal tract. To determine if somatostatin directly alter the action of vasopressinn we studied the effects of this polypeptide on vasopressin-stimulated transport processes in the toad urinary bladder in vitro. Somatostatin produced a dose-dependent, reversible inhibition of vasopressin-stimulated osmotic water flow; it inhibited theophylline-stimulated osmotic water flow but not the water flow stimulated by 8-p-chlorophenylthioadenosine 3',5'-cyclic monophosphate. These data are consistent with an inhibition of both basal and hormone-stimulated adenylate cyclase. Vasopressin-stimulated short circuit current was not inhibited by somatostatin. These studies provide direct evidence for an effect of somatostatin on hormone-modulated epithelial transport in tissues other than the gastrointestinal tract. We propose that endogenous somatostatin may function as a local regulator of the cellular action of vasopressin on osmotic water flow.

Rectifying properties of the membrane of single freshly isolated smooth muscle cells

Abstract: Single smooth muscle cells freshly isolated from the stomach muscularis of the toad Bufo marinus were studied under direct microscopic observation using intracellular microelectrodes. The deviation...

Effect of quinidine on Na, H+, and water transport by the turtle and toad bladders.

Abstract: The effect of quinidine on Na and H+ transport by the turtle bladder and water transport by the toad bladder was examined. Quinidine inhibited the short-circuit current and the potential difference in a dose-dependent fashion. The effect of quinidine on the short-circuit was not dependent on extracellular calcium concentration and was not reversible with removal of the drug. Quinidine inhibited H+ secretion in a dose-dependent fashion. The effect of quinidine on H+ secretion also was not dependent on extracellular calcium concentration and was not reversible, either with removal of the drug or with stimulation of H+ secretion with 5% CO2. The effect of quinidine on Na or H+ transport could not be elicited by an equivalent dose of tetracaine, suggesting that the inhibitory effect of quinidine is not dependent on its anesthetic properties. Quinidine also inhibited vasopressin and cyclic AMP stimulated water flow in the toad bladder. Quinidine did not alter calcium uptake by the turtle bladder but increased calcium efflux by the turtle and toad bladders. These observations suggest that a rise in cytosolic calcium is responsible for the inhibitory effect of quinidine on Na, H+, and water transport.

Relationship of transient electrical properties to active sodium transport by toad urinary bladder

Abstract: Application of voltage pulses of 10 mV for periods of 9 sec across toad urinary bladder elicits a rapid deflection in transepithelial current. Frequently, the current decays back towards its baseline value during the course of the polarizing pulse. This transient phenomenon can be induced, or its magnitude increased, by raising the mucosal or serosal Na+ concentration. The transient can be abolished by sufficiently hyperpolarizing the tissue (rendering serosa positive to mucosa), by inhibiting transcellular Na+ transport with amiloride or ouabain, and by increasing the serosal K+ concentration. Vasopressin increases net Na+ movement across toad bladder but does not elicit these transients. It is proposed as a working hypothesis for further study that the transient behavior characterized in this study reflects: (1) the partition of Na+ between the apical plasma membrane and contiguous fluid layers, (2) the partition of K+ between the basolateral plasma membrane and adjacent submucosal fluid layer, and (3) the negative feedback interaction between intracellular Na+ activity and Na+ permeability of the apical plasma membrane of the transporting cells.

Effect of amiloride on conductance of toad urinary bladder.

Abstract: The transepithelial conductance of toad bladder epithelia and the amplitude of the fluctuations of this conductance caused by the action of the underlying smooth muscle have been further investigated. In particular, amiloride was found to reduce both tissue conductance and its fluctuating component to the same extent. Analysis suggests that the steady-state conductance of the toad urinary bladder may be associated only with the paracellular pathway for ions.

Chapter 16 The Effects of Voltage Clamping on Ion Transport Pathways in Tight Epithelia

Abstract: Publisher Summary This chapter describes and presents evidence that the resistance of the shunt pathway in toad urinary bladder and skin changes during the passage of current and that this change is voltage and time dependent. The studies in toad urinary bladder reported in this chapter, however, indicate that there is no change in the resistance of the cellular pathway. These studies make it clear that in both toad skin and toad urinary bladder the decrease in resistance during passage of a transepithelial pulse is accompanied by an increase in the transepithelial flux through the extracellular pathway. The increase in transepithelial serosa-to-mucosa sodium flux induced by voltage or current clamping indicates an increase only in the conductance of the paracellular pathway. Because the conductance of the paracellular pathway is a function, at least in part, of the transport properties of the tissue, one way to reconcile the changes described in the chapter might be to assume that the inhibition of transport brought about by voltage clamping directly affects the shunt pathway. However, it is not yet clear that the change in conductance represents a universal phenomenon in other tight epithelia despite the fact that toad skin seems to share the same characteristics as the urinary bladder.

Chapter 7 Intracellular Chemical Activity of Potassium in Toad Urinary Bladder

Abstract: Publisher Summary Intracellular recording with K + -selective microelectrodes helps to clarify the relationship between potassium accumulation and transepithelial transport of sodium. This chapter describes the quantitative significance of the possible impalement-induced loss of intracellular potassium. The intracellular chemical activity of potassium within the urinary epithelium of toad and frog bladder has been reported to be surprisingly low. The intracellular contents of potassium and chloride are thought to exchange far more slowly across the apical than across the basolateral plasma membrane; therefore, changes in the potassium and chloride concentrations of the mucosal media bathing voltage-clamped tissue are not likely to affect the corresponding intracellular activities seriously. Previous measurements of changes in intracellular potassium activity, associated with inhibition of active sodium transport, have suggested that cellular potassium accumulation and the net sodium transport across toad urinary bladder proceed by two different transfer mechanisms. Although the measurements performed were of potassium activity and short circuit current, a number of considerations indicate that the results reflect a true dissociation of transepithelial sodium transport and cellular potassium accumulation.

Gluconeogenesis in toad gastric mucosa

Abstract: 1. 1. The gluconeogenic activity in the gastric mucosa of the toad Bufo marinus was investigated. 2. 2. The gastric mucosa was shown to contain significant levels of activities for pyruvate carboxylase, phosphoenolpyruvate carboxykinase, fructosediphosphatase and glucose-6-phosphatase, four important gluconeogenic enzymes. 3. 3. The glucose content of the gastric mucosa was significantly increased by pyruvate, alanine, succinate and glutamate. The rate of glucose formation from pyruvate (0.5 μmol/hr per g wet weight) was approx 2% of rates observed for rat liver. 4. 4. Significant incorporation of H 14 CO 3 − into glycogen was demonstrated in the presence of pyruvate. 5. 5. The results indicate that significant gluconeogenic activity occurs in the toad gastric mucosa.

Isolation of epithelial cells from toad bladder.

Abstract: The epithelial cells of the toad bladder have been isolated by brief exposure to ethylenediaminetetraacetic acid followed by treatment with collagenase, DNAse, and the application of shearing forces. This approach eliminates the need for scraping of the mucosal surface and reduces mechanical damage during harvesting of the epithelium. The method yields intact, isolated epithelial cells and few clumps. The three major types of epithelial cells described in the intact toad bladder were present in the final preparation. The cellular contents of nucleic acids and proteins (in pg/cell) were: DNA 22.5 +/- 1.1; RNA, 12.9 +/- 0.6; and protein, 192 +/- 9. The isolated cells possess rates of oxygen consumption and amino acid incorporation higher than those of epithelial sheets obtained by collagenase treatment and scraping of the intact bladder. However, the production of cyclic nucleotides in response to stimulation by vasopressin and carbachol is comparable in both preparations.

Rhythmic electrical activity in stomach and intestine of toad

Abstract: The intact stomach of the toad initiates rhythmic slow-spikes of 5–15 s duration and frequency of 3-5 min −1 . The spontaneous electrical waves originate in the longitudinal muscle layer; isolated circular muscle is quiescent. Aboral conduction velocity is 0.12–0.9 mm s −1 . Reduction of external sodium concentration from 89.5 to 15 mM produced no effect on slow spikes, although further reduction to 1.5 mM increased frequency and decreased amplitude. Slow-spikes were unaffected by ouabain or by incubation in potassium-free solution. When calcium in the medium was reduced, slow-spike amplitude and frequency decreased. Slow-spikes exhibited a change in amplitude of 16 mV per decade change in Ca O 2+ ; slow-spikes were eliminated at 10 −8 M Ca O 2+ and by blockers of calcium conductance channels. Intact intestine of toad demonstrated slow-waves which resembled those of mammalian intestine. These were sensitive to changes in external sodium and were eliminated by 1 × 10 −4 M ouabain. It is suggested that rhythmic slow-spikes of longitudinal smooth muscle of amphibian stomach may result from periodic changes in Ca conductance whereas endogenous electrical waves of intestine may result from rhythmic extrusion of sodium.