Activation by intracellular calcium of a potassium channel in cardiac sarcoplasmic reticulum.
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Pflugers Arch 417 (6): 651--653 (February 1991)

The effects of low (pCa 7.5 to 3) concentrations of intracellular calcium ion on a single potassium channel in the sarcoplasmic reticulum of canine heart ventricular muscle were investigated using a planar lipid bilayer technique. The low concentrations were obtained by mixing EGTA and calcium chloride. By varying the pCa of the cytoplasmic face between 3 to 7.5, two novel effects were observed. First, an increase in the intracellular Ca$^2+$ concentration produced an increase in the unit current amplitude of open states; the voltage-current relationship was ohmic at these concentrations. Second, an increase in the Ca$^2+$ concentration increased the open probability. Both these effects of Ca$^2+$ were dose-dependent, and were consistently observed in all channels tested. Thus, the SR potassium channel observed appears to belong to the class of Ca$^2+$-activated potassium channels.
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