Abstract
In this study terminal cisternae vesicles from rabbit skeletal muscle were fused into planar bilayers and the effect of calmodulin on single Ca 2+ release channel currents was investigated. In the presence of 10 −7 and 10 −9 M free [Ca 2+], nanomolar concentrations of calmodulin activated the channel by increasing the open probability of single-channel events in a dose dependent manner. The activatory effect of calmodulin was reversed by 10 μM ruthenium red. At 10 −5 M free [Ca 2+], calmodulin (0.1-1 μM) inhibited channel activity. Calmodulin overlays were carried out using concentrations of Ca 2+ similar to those used for the planar lipid bilayer assays. In the presence of 10 −7 M [Ca 2+], calmodulin bound to the ryanodine receptor, to a region defined by residues 2937-3225 and 3546-3655. These results suggest that calmodulin may activate the Ca 2+-release channel (ryanodine-receptor) by interacting with binding sites localized in the central portion of the RYR protomer.
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