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Regulation of phosphorylation of a specific protein in toad-bladder membrane by antidiuretic hormone and cyclic AMP,
Abstract:
Phosphorylation of a specific protein was decreased in intact toad bladders by exposure to either antidiuretic hormone or monobutyryl cyclic AMP. The decrease in phosphorylation caused by these agents preceded the change in electrical potential difference (an indicator of the rate of sodium ion transport) observed in response to the same compounds. The addition of cyclic AMP to homogenates of toad bladder led to a decrease in phosphorylation of the same, or a similar, protein. In subcellular fractionation studies, the effect of cyclic AMP on the phosphorylation of this protein was observed in those fractions rich in membrane fragments, but not in the nuclear or cell-sap fractions. These and other results are compatible with the possibility that the regulation by vasopressin and cyclic AMP of sodium and/or water transport in toad bladder may be mediated through regulation of the phosphorylation of this specific protein.
Insights
Antidiuretic hormone and cyclic AMP reduce protein phosphorylation in toad bladders, potentially mediating sodium and water transport regulation. This molecular change precedes observable transport effects, suggesting a key signaling role.
Area of Science:
- Physiology
- Molecular Biology
- Cell Signaling
Background:
- Antidiuretic hormone (ADH) and cyclic AMP (cAMP) are known regulators of water and ion transport in epithelial tissues like the toad bladder.
- The precise molecular mechanisms by which these signaling molecules exert their effects are not fully elucidated.
Purpose of the Study:
- To investigate the role of protein phosphorylation in the physiological response of toad bladders to antidiuretic hormone and cyclic AMP.
- To identify the specific protein(s) and cellular localization involved in this regulatory pathway.
Main Methods:
- Experiments were conducted on intact toad bladders and bladder homogenates.
- Measurements included protein phosphorylation levels and electrical potential difference (sodium transport indicator).
- Subcellular fractionation was used to determine the localization of the observed effects.
Main Results:
- Exposure to antidiuretic hormone or monobutyryl cyclic AMP decreased the phosphorylation of a specific protein in intact toad bladders.
- This decrease in phosphorylation occurred before the change in electrical potential difference.
- Cyclic AMP also decreased the phosphorylation of the same protein in homogenates, with the effect localized to membrane-rich fractions.
Conclusions:
- The results suggest that vasopressin (via ADH) and cyclic AMP may regulate sodium and/or water transport in the toad bladder by modulating the phosphorylation state of a specific protein.
- This protein is likely located in the membrane fraction of the cells.