Antidiuretic Hormone Modulates Membrane Phosphoproteins in Toad Urinary Bladder and Retrieved Water Channel Containing Apical Membrane Vesicles
|Title:||Antidiuretic Hormone Modulates Membrane Phosphoproteins in Toad Urinary Bladder and Retrieved Water Channel Containing Apical Membrane Vesicles|
|Author:||Harris, H. William|
|Publisher:||Journal of the American Society of Nephrology|
|Date Published:||March 01, 1991|
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This translation by the NDI Foundation is to assist the lay reader. To provide a clear, accessible interpretation of the original article, we eliminated or simplified some technical detail and complicated scientific language. We concentrated our translation on those aspects of the article dealing directly with NDI. The NDI Foundation thanks the researchers for their work toward understanding and more effectively treating this disorder.
© Copyright NDI Foundation 2007 (JC)
As the water flows across the cell membrane through the WCs, bits of the apical membrane are taken inside the cell and the apical membrane is restored to its normal state of low water permeability. The bits of apical membrane contain vesicles which contain WCs. Thus, it is the retrieval of WCs from the apical membrane back to inside the cell that returns the apical membrane to its normal, low water permeable state.
Harris wanted to discover in more detail the structure and function of some of the proteins of the toad bladder and see if and how they related to the process of WC retrieval from the apical membrane. He knew that three phosphoproteins, each with different molecular mass (a 34 kilodalton (kDa) protein, a 28 kDa protein and a 17 kDa) increased in phosphate content when stimulated with ADH. And he knew a 15.5 kDa phosphoprotein was reduced to about half its original phosphate content when the WCs are retrieved from the apical membrane when the increased water flow across the apical membrane occurs. (This process is called flux inhibition because it reduces the permeability of the apical membrane and thus reduces the water flow across it.)
Harris confirmed that all four of these phosphoproteins are present in the membrane of granular cells. He found that the 28 and 17 kDa proteins were integral membranes proteins. That is, they were embedded in the cell membranes. The author could not, however, determine their function, but he did determine that these two phosphoproteins were not components of retrieved apical membrane proteins.
In contrast, the 34 kDa and the 15.5 kDa proteins are peripheral membrane proteins, which are merely attached to - not embedded in - the membranes. The 15.5 kDa protein is attached to the outside surface of retrieved apical membrane vesicles containing WCs. Harris speculates that this protein may play a role in the retrieval of vesicles from the apical membrane in response to ADH-elicited water flow during flux inhibition.