Toad

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

Identification of aldosterone-induced proteins in the toad's urinary bladder.

Abstract: Aldosterone (the 8,11-hemiacetal 0f 11beta,21-dihydroxy-3,20-dioxo-4-pregnen-18-al) markedly stimulates sodium transport in a number of epithelial tissues. We have attempted to determine whether aldosterone induces the synthesis of specific protein(s) in the course of its action upon the toad urinary bladder. Paired hemibladders were incubated in media containing either [3H]methionine or [35S]methionine; aldosterone in physiologic concentrations was added to one bath and, after incubation, the intact "mitochondria-rich" (MR) and "granular" (G) mucosal cells were isolated. The ratio (3H/35S) was used to identify proteins whose synthesis was induced in the mucosal cells of the steroid-treated bladders. Using exclusion gel chromatography and isoelectric focusing, we identified several aldosterone-induced proteins in the supernatant (105,000 x g) fraction of the MR cell. None was evident in this fraction of the G cell. These proteins have apparent molecular weights ranging from 17,000 to 38,000 and the isoelectric point of the major component is 4.5. Corticosterone (11beta,21-dihydroxy-4-pregnene-3,20-dione) induced the synthesis of proteins in the G cells, but none of these proteins was similar in molecular weight to the aldosterone-induced proteins in the MR cell. Our findings support the hypothesis that aldosterone induces the synthesis of specific proteins and indicate that, in this tissue, these proteins are synthesized by the MR cell.

Electrical excitability of isolated frog skin and toad bladder.

Abstract: When current of proper polarity and sufficient intensity is passed across isolated frog skin or toad bladder, an action potential of about 200 mv and 10 msec. duration with a sharp threshold and refractory period of several seconds' duration is elicited. Interruption of current during the action potential abolishes the response, and, as shown by appropriate bridge measurements, this occurs because the action potential results from resistance variations during the current flow. The ionic composition of the medium bathing the frog skin was varied, and it was found that the response is relatively insensitive to changes in the solution bathing the inner surface, but rapidly and reversibly affected by changes in the outer solution, particularly by replacement of sodium with potassium and by variations of calcium concentration. It was also observed that the resistance of the skin and action potential across it are reversibly altered by metabolic inhibitors and that these alterations occur independently of any changes in the intrinsic EMF of the system. From the finding that the action potential across frog skin and toad bladder results from a time-variant resistance, it is argued that this same phenomenon can be the basis of electrical excitability in general. This would attribute physical significance to the equivalent circuit commonly employed to represent the plasma membrane; i.e., the plasma membrane would be a mosaic structure of spatially separate permselective regions.