Toad

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

Response properties of the toad retinal pigment epithelium

Abstract: Electrophysiologic responses were recorded in vitro from the retina of the toad, Bufo marinus. In the isolated retinal pigment epithelium (RPE)-choroid preparation, a decrease in the K + concentration outside the apical membrane evoked a sequence of trans-epithelial (TEP) and membrane potential changes. A hyperpolarization originating at the RPE apical membrane that increased the TEP was followed by a delayed hyperpolarization originating at the basal membrane that decreased the TEP. This response sequence differed from the well-studied bullfrog RPE in exhibiting potentials generated at the basal membrane; it more closely resembleed responses from the reptilian and avian RPE. The toad direct-current electroretinogram recorded from a neural retina-RPE-choroid preparation also differed from other amphibians and was more similar to responses recorded in reptiles, birds, and mammals. In this initial study, the electrophysiologic characteristics of the RPE's Na + /K + pump were examined. Contrary to a previous report, ouabain, a specific inhibitor of the pump, depolarized the apical membrane and decreased the TEP. Ba 2+ was used to block apical K + conductance and unmasked a modulation of the Na + /K + pump by subretinal K + . Decreasing the K + concentration in the presence of Ba 2+ depolarized the apical membrane and decreased the TEP. These responses were blocked by ouabain, indicating that the K + concentration decrease slowed the Na + /K + pump. Invest Ophthalmol Vis Sci 31:2353-2360, 1990 The retinal pigment epithelium (RPE) consists of a single layer of cells whose apical membrane faces the neural retina and whose basal membrane faces the choroid. This report describes responses from the toad, Bufo marinus, and establishes the toad retina as a novel amphibian model. Two different RPE response patterns have been evoked by light stimulation of the vertebrate neural retina and recorded in the direct-current electroretinogram (DC-ERG), depending on the species. In fish and amphibians that have been studied previously (carp, eel, frog, and newt), the DC-ERG is relatively simple; after the aand b-waves of the ERG, the c-wave rises to a peak and then slowly decays toward the dark-adapted baseline. 1 ' 2 In reptiles, birds, and mammals, after the peak of the c-wave, there is a trough, the fast-oscillation trough, and then a slow rise to the light peak. 13 " 5 Intracellular RPE recordings in the cat, chick, and gecko show that the fast-oscillation trough and the light peak are generated by potentials that originate primarily at the RPE basal membrane. 3 ' 5 However, the study of basal membrane mechanisms has been

Plasma potassium may protect sodium pumps of toad hearts from an endogenous inhibitor

Abstract: Resibufogenin (3-hydroxy-14,15-epoxy-20,22-dienolide glycoside) is a potent sodium pump inhibitor present in toad toxin. It is present in the skin of the cane toad (Bufo marinus) at a concentration equivalent to ouabain of approximately 1 mM. Because toads, like other amphibians, have permeable skin, resibufogenin is also found in high concentrations in the blood. In the cane toad the blood concentration is estimated to be 1 microM (D. Lichtstein, S. Kachalsky, and J. Deutsch. Life Sci. 38: 1261-1270, 1986; D. Lichtstein, S. Samuelov, J. Deutsch, H. Xu, R. A. Lutz, S. S. Chernick and S. S. Chernick. Klin. Wochenschr. 65, Suppl. 8: 40-48, 1987), a concentration thousands of times that required to produce toxicity in humans (J. S. Flier, E. Matatos-Flier, J. A. Pallotta, and D. McIsaac. Nature Lond. 279: 341-343, 1979). In examining how the cane toad avoids inhibiting its own sodium pumps, work on the heart showed that 1) cane toads possess a similar number of cardiac sodium pumps as other vertebrates, and 2) normal plasma K+ levels completely prevent ouabain, and presumably resibufogenin, from binding to cardiac sodium pumps of the cane toad. Other species, i.e., rat (Rattus norvegicus) and salamander (Ambystoma mexicanum), did not show K+ protection of their cardiac ouabain binding sites up to normal plasma K+ levels. These species do not possess the high level of endogenous ouabain-like substance found in the toad. K+ demonstrated a capacity to protect the enzymatic activity of the toad heart sodium pumps from the inhibitory effects of ouabain.

A comparison between field habits and contractile performance of frog and toad sartorius muscle

Abstract: The contractile characteristics of the sartorius muscle isolated from the frog,Rana pipiens, and the toad,Bufo americanus, are compared at 25°C and pH 8.0. Frog sartorius muscles have faster shortening velocities and greater mechanical power at low loads, while toad sartorius muscles develop greater tetanic tension (Fig. 1). During the rising phase of an isometric tetanus, the latent period and time to half-maximum tension are shorter and the rate of tension development is faster in frog sartorius muscles than in toad sartorius muscles (Table 1). There is no difference between the two species during relaxation, i.e., the half-relaxation time after an isometric tetanus is quite similar (Table 1). It is concluded that most of the contractile characteristics of frog and toad sartorius muscles correlate well with the habits, jumping ability, burrowing activities and endurance to fatigue of the two species in the field.