Amiloride-sensitive sodium channel

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Amiloride-sensitive sodium channels are certain proteins that are located in the membrane of some cells and serve in the transport of sodium ions across the membrane.

[edit] Structure

The polypeptide chain is comprised of approximately 700 amino acids. Both the N and C termni are intracellular. It contains 2 hydrophobic membrane spanning regions and also has an extracellular loop that contains many cysteine residues that are conservatively spaced.

[edit] Location

These receptors are located in the lining of the distal tubule of the kidney, tongue epithelium, and proximal to aortic baroreceptors.

[edit] Function

These are sodium ion channels that serve in transport of sodium in non-excitable tissues. They are voltage-insensitive. In kidney tubules, these channels play a major role in sodium absorption from urine and their activity is modulated by aldosterone and antidiuretic hormone (ADH). In the case of ADH, the expression of this channel is increased. The function of this channel is inhibited by amiloride, intracellular protons, intracellular calcium, calcium-dependent protein kinase, and nitriuretic peptide (ANP). Channel expression is stimulated by cAMP, ADH, aldosterone, and PIP2. In tongue epithelia, these channels play a role in signal transduction associated with a sense of salty(sodium ions) or acidic (hydrogen ions) taste. Both sodium ions and hydrogen ions may travel through these channels. The gamma subunit of this particular sodium channel is also localized in the mechanotransduction site of the nerve terminals of the aortic baroreceptors. These channels facilitate signal transduction from the baroreceptors located in the aortic bodies. Therefore they play an important role in blood pressure regulation. Because amiloride can block these channels it is commonly used as a medication to reduce blood pressure.