Toad

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

Partition of Tissue Functions in Epithelia: Localization of Enzymes in "Mitochondria-Rich" Cells of Toad Urinary Bladder

Abstract: The mucosal epithelium of the toad urinary bladder reabsorbs sodium, acidifies the urine, and is responsive to neurohypophyseal hormnones. Mucosal epithelial cells, consisting of two major morphologic cell types, "mitochondria-rich" and "granular," were removed from the bladder and separated by density gradient centrifugation. The mitochondria-rich cells contained three times as much carbonic anhydrase activity as the granular cells. Oxytocin caused a 235 percent increase in the adenosine 3',5'-monophosphate content of mitochondria-rich cells but had no effect on the granular cells. The evidence indicates that the mitochondria-rich cell, which accounts for only 15 percent of the mucosal cells, plays a major role in the mediation of sodium ion and hydrogen ion transport in the toad bladder and is a specific site of action of neurohypophyseal hormones.

Site of action of aldosterone on the bladder of the toad.

Abstract: THE active transport of sodium by the urinary bladder of the toad, Bufo marinus, is increased when the animal1 or the membrane itself2–4 is treated with aldosterone. Antidiuretic hormone also increases active sodium transport by the isolated toad bladder5 ; this hormonal stimulation has been ascribed to a facilitated passive movement of sodium from the incubation solution on the mucosal side into the epithelial cells of the membrane6 ; as a result, there is an increase of that fraction of tissue sodium concerned with the transfer of this ion across the preparation. Hence the acceleration of the active extrusion of sodium, at the serosal border of the epithelial cells, can be taken as a mere consequence of an increased concentration of substrate—namely sodium—made available to the ‘pump’.

Regulatory Role of Intracellular Calcium Ions in Epithelial Na Transport

Abstract: Whereas several early studies indicated that extracellular calcium levels can influence the rate of sodium movement across amphibian epithelia (15, 16), only during the last decade has it become apparent that cytosolic calcium ions are potentially important regulators of transepithelial ion and water transport. The first suggestive evidence that intracellular calcium ions play such a role was obtained in studies with quinidine in the urinary bladder of the toad (46). Quinidine, an agent presumed to increase the level of cytosolic free calcium ions (4, 29, 10,22), was found to inhibit vasopressin­ dependent water permeability and net sodium transport across the isolated toad bladder (46,50). Subsequently, Erlij & Grinstein (18, 25) reported that a reduction in the sodium concentration of the medium bathing the inner surface of the isolated frog skin inhibits the rate of active transepithelial sodium transport in a calcium-dependent manner. Their interpretation of this finding was based on the concept that a Na-Ca exchange mechanism operates across the basolateral border of epithelial cells, as in excitable cells, as originally proposed by Blaustein (7). Wiesmann et al (56) employed the ionophore A23187 to explore the regulatory role of intracellular calcium in the toad bladder; these investigations first described and characterized the

Polymorphism in purified guanylate cyclase from vertebrate rod photoreceptors

Abstract: Guanylate cyclase from rod photoreceptors of amphibian (toad, Bufo marinus, and frog, Rana catesbeiana) and bovine retinas was solubilized and purified by a single chromatography step on a GTP-agarose column. Silver staining of purified amphibian enzymes in SDS/polyacrylamide gels disclosed a doublet band (110 and 115 kDa), while the bovine enzyme appeared as a singlet band (110 kDa). The identification of these guanylate cyclases was confirmed using three chromatography systems with the purified enzymes. Specific binding to Con A-Sepharose suggested that rod guanylate cyclase is a glycoprotein. Two-dimensional gel electrophoresis of purified toad, frog, and bovine enzymes resolved two, three, and five variants, respectively, that differed in isoelectric point. Two variants of toad guanylate cyclase showed differences in various characterizations. These data suggest multiple mechanisms for regulation of guanylate cyclase activity in vertebrate rod photoreceptors.