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Biophysical Journal 60: 198-203 (1991)
© 1991 the Biophysical Society

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Blockade of cardiac sarcoplasmic reticulum K+ channel by Ca2+: two-binding-site model of blockade.

Q Y Liu and H C Strauss

Department of Pharmacology, Duke University Medical Center, Durham, North Carolina 27710.

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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Copyright © 1991 by the Biophysical Society.