Toad

About: Toad is a research topic. Over the lifetime, 1624 publications have been published within this topic receiving 28732 citations.

Effects of Pb2+ ions on Na+ transport in the isolated skin of the toad Pleurodema thaul.

Abstract: The effects induced by lead ions on the short-circuit current (SCC) and on the potential difference (V) of the toad Pleurodema thaul skin were investigated. Pb2+ applied to the outer (mucosal) surface increased SCC and V and when applied to the inner (serosal) surface decreased both parameters. The stimulatory effect, but not the inhibitory action, was reversible after washout of the metal ion. The amiloride test showed that the increase was due principally to stimulation of the driving potential for Na+ (V-E(Na+)) and that inhibition was accompanied by a reduction in the V-E(Na+) and also by a significant decrease in skin resistance indicating possible disruption of membrane and/or cell integrity. The effect of noradrenaline was increased by outer and decreased by inner administration of Pb2+. The results suggest that mucosal Pb2+ activates toad skin ion transport by stimulating the V-E(Na+) and that serosal Pb2+, with easier access to membrane and cellular constituents, inactivates this mechanism, revealing greater toxicity when applied to the inner surface of the skin.

[Calcium-dependent chloride channels in plasma membrane of oocytes from toad, Bufo bufo gargarizans].

Abstract: In this paper, membrane current properties of the fully-grown oocytes from toad, Bufo bufo gargarizans, were studied by using two-microelectrode voltage clamp technique Axion of adult female toad was destroyed, and then ovarian lobes containing oocytes in stage I to VI were removed and incubated in Ca(2+)-free ND96 solution with collagenase (15 mg/ml) for 1 h Subsequently, the oocytes were washed in Ca(2+)-free ND96 solution for 10 min to completely remove the follicular layer For the experiments only the oocytes in stage V and VI were selected and used during 1 to 5 d The membrane was depolarized from a holding potential of -80 mV to +60 mV in 10 mV step It was found that a sustained outward current was elicited by depolarization Potassium channel blockers (tetraethylammonium chloride, TEA, 10 mmol/L and 4-aminopyridine, 4-AP, 10 mmol/L) reduced the outward current to (234+/-072)% of the maximum However, further addition of chloride channel blocker (5-nitro-2, 3-phenypropylamino benzoate, NPPB, 30 micromol/L) could almost completely block the outward current to (21+/-008)% of the maximum In the presence of TEA and 4-AP, removal of extracellular Ca(2+) or adding verapamil (40 micromol/L), could also reduce the outward current to (22+/-004) % and (31+/-015) % of the maximum, respectively It is concluded that calcium-dependent chloride channels exist in plasma membrane of Bufo bufo gargarizans oocytes, besides potassium channels

The gonadotropin-releasing hormone (GnRH) neuron system of the clawed toad Xenopus laevis.

Abstract: The GnRH immunoreactive (GnRH-ir) neuronal system of the Clawed toad Xenopus laevis was studied and compared with the GnRH-ir system of the frog Rana esculenta. Polyclonal antibodies against mammalian (mGnRH) and chicken type-II GnRH (cGnRH-II), and monoclonal antibodies against mGnRH were used in the study. In the Xenopus laevis, most of the immunopositive neuronal cell bodies were located in telencephalic (35-50 per cent) and diencephalic areas (50-65 per cent). About 15-20 per cent of the GnRH perikarya appeared in mesencephalic tegmental regions. Besides the larger GnRH fiber tracts present also in mammals, the toad has rich mGnRH immunopositive axon population in the mesencephalon and in the upper part of the medulla. A similar distribution of the GnRH-ir neuronal elements exists in Rana esculenta, but the number of stained cells and fibers was less. Specificity of the staining of cGnRH-IIir structures located in the lower brainstem could not be proved and therefore the study is only restricted to the findings with mGnRH-antibodies.