Toad

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

Binding of aldosterone by mitochondria-rich cells of the toad urinary bladder.

Abstract: ALDOSTERONE causes a large increase in the active transport of sodium by the urinary bladder1 of the toad. This response, analogous to the effects of the steroid on the kidney, has been the object of considerable biochemical study2. Aldosterone also enhances the stimulation by neurohypophyseal hormones of sodium and hydro-osmotic flux3,4. Because the response in sodium transport seems quantitatively related to the increment of cyclic AMP generated by vasopressin5, augmentation of the sodium response is presumably related to the larger increment of intracellular nucleotide induced by a given dose of vaso-pressin in steroid-treated bladders6. Using a technique for separating the two major cell types of the bladder mucosal epithelium—the granular (G) and the mitochondria-rich (MR) cells—we found that a response to neurohypophyseal hormones, as reflected by hormone-induced increases in the intracellular cyclic AMP content, is apparently limited to the MR cell7. This apparent synergism of the neurohypophyseal and steroid hormones on transport suggests that their loci of action are in close proximity. We therefore examined the binding of 3H-aldosterone by the two major cell types.

Tubular system volume changes in twitch fibres from toad and rat skeletal muscle assessed by confocal microscopy.

Abstract: The volume of the extracellular compartment (tubular system) within intact muscle fibres from cane toad and rat was measured under various conditions using confocal microscopy. Under physiological conditions at rest, the fractional volume of the tubular system (t-sys(Vol)) was 1.38 +/- 0.09% (n = 17),1.41 +/- 0.09% (n = 12) and 0.83 +/- 0.07% (n = 12) of the total fibre volume in the twitch fibres from toad iliofibularis muscle, rat extensor digitorum longus muscle and rat soleus muscle, respectively. In toad muscle fibres, the t-sys(Vol) decreased by 30% when the tubular system was fully depolarized and decreased by 15% when membrane cholesterol was depleted from the tubular system with methyl-beta-cyclodextrin but did not change as the sarcomere length was changed from 1.93 to 3.30 mum. There was also an increase by 30% and a decrease by 25% in t-sys(Vol) when toad fibres were equilibrated in solutions that were 2.5-fold hypertonic and 50% hypotonic, respectively. When the changes in total fibre volume were taken into consideration, the t-sys(Vol) expressed as a percentage of the isotonic fibre volume did actually decrease as tonicity increased, revealing that the tubular system in intact fibres cannot be compressed below 0.9% of the isotonic fibre volume. The results can be explained in terms of forces acting at the level of the tubular wall. These observations have important physiological implications showing that the tubular system is a dynamic membrane structure capable of changing its volume in response to the membrane potential, cholesterol depletion and osmotic stress but not when the sarcomere length is changed in resting muscle.