Abstract
Gating properties of the Ca 2+ channel in sarcoplasmic reticulum (SR) were monitored by measuring the choline permeation of the heavy fraction of SR (HSR) vesicles by the light scattering method. Increase of choline permeation by micromolar Ca 2+, which refers to Ca 2+ response, was lost when HSR vesicles were incubated overnight with EDTA or EGTA. In parallel, calsequestrin was released from the vesicles. This loss of Ca 2+ response could not be inhibited by millimolar Mg 2+, but was partially inhibited by submolar KCl. Since it took 3-5 hours to lose the Ca 2+ response, calsequestrin may be released from the inside of the vesicles. When HSR vesicles were incorporated into lipid bilayer, open probability of the Ca 2+ channel increased when calsequestrin was added to the trans side in the presence of millimolar Ca 2+.These results suggest that calsequestrin acts as a regulator of Ca 2+ channel in SR membrane.
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