Abstract |
125I-Apamin and photolabile derivatives of the toxin have been used to investigate the binding properties and subunit composition of small conductance Ca2+-activated potassium channels (SK(Ca) channels) expressed on plasma membranes from rat brain, rabbit liver, or rat pheochromocytoma (PC12) cells. On all preparations, 125I-apamin recognized single classes of acceptor binding sites with similar high affinity (Kd approximately 3-6 pM). Gallamine, however, was found to readily discriminate between 125I-apamin acceptors present in these preparations, showing a maximal approx nine-fold difference in affinity for acceptors expressed by rabbit liver or PC12 cells. Affinity-labeling patterns revealed the expression of different hetero-oligomeric combinations of high (86 or 59 kDa) and low (33 or 30 kDa) molecular mass 125I-apamin-binding polypeptides, consistent with pharmacological differences. Alternative expression of either 86- or 59-kDa polypeptides appeared to be the most important factor influencing gallamine's affinity for SK(Ca) channel subtypes. Both high- and low-molecular-mass polypeptides are integral membrane proteins, the latter being glycosylated in a tissue-specific manner.
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Authors | J D Wadsworth, S Torelli, K B Doorty, P N Strong |
Journal | Archives of biochemistry and biophysics
(Arch Biochem Biophys)
Vol. 346
Issue 1
Pg. 151-60
(Oct 01 1997)
ISSN: 0003-9861 [Print] United States |
PMID | 9328295
(Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)
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Chemical References |
- Affinity Labels
- Potassium Channels
- Potassium Channels, Calcium-Activated
- Small-Conductance Calcium-Activated Potassium Channels
- Apamin
- Gallamine Triethiodide
- Calcium
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Topics |
- Affinity Labels
- Animals
- Apamin
(metabolism)
- Brain Chemistry
- Calcium
(pharmacology)
- Gallamine Triethiodide
(metabolism)
- Ion Channel Gating
- Liver
(chemistry)
- PC12 Cells
- Potassium Channels
(chemistry, classification, metabolism)
- Potassium Channels, Calcium-Activated
- Rabbits
- Rats
- Small-Conductance Calcium-Activated Potassium Channels
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