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  • Title: Blockade of cardiac sarcoplasmic reticulum K+ channel by Ca2+: two-binding-site model of blockade.
    Author: Liu QY, Strauss HC.
    Journal: Biophys J; 1991 Jul; 60(1):198-203. PubMed ID: 1883938.
    Abstract:
    Potassium countercurrent through the SR K+ channel plays an important role in Ca2+ release from the SR. To see if Ca2+ regulates the channel, we incorporated canine cardiac SR K+ channel into lipid bilayers. Calcium ions present in either the SR lumenal (trans) or cytoplasmic (cis) side blocked the cardiac SR K+ channel in a voltage-dependent manner. When Ca2+ was present on both sides, however, the block appeared to be voltage independent. A two-binding site model of blockade by an impermeant divalent cation (Ca2+) can explain this apparent contradiction. Estimates of SR Ca2+ concentration suggest that under physiological conditions the cardiac SR K+ channel is partially blocked by Ca2+ ions present in the lumen of the SR. The reduction in lumenal [Ca2+] during Ca2+ release could increase K+ conductance.
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