Activation by intracellular calcium of a potassium channel in cardiac sarcoplasmic reticulum.
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 Ca2+ 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 Ca2+ concentration increased the open probability. Both these effects of Ca2+ were dose-dependent, and were consistently observed in all channels tested. Thus, the SR potassium channel observed appears to belong to the class of Ca2(+)-activated potassium channels.
Uehara
A
A
Department of Physiology, School of Medicine, Fukuoka University, Japan.
Yasukohchi
M
M
Ogata
S
S
Imanaga
I
I
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002122:Calcium Chloride / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D006352:Heart Ventricles / Q000166:cytology*; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000502:physiology*
D015221:Potassium Channels; D002122:Calcium Chloride; D002118:Calcium