CALCIUM-DEPENDENT ACTIVATION OF SKELETAL-MUSCLE CA2+ RELEASE CHANNEL (RYANODINE RECEPTOR) BY CALMODULIN

In this study terminal cisternae vesicles from rabbit skeletal muscle were fused into planar bilayers and the effect of calmodulin on single Ca2+ release channel currents was investigated. In the presence of 10 (-7) and 10(-9) M free [Ca2+], nanomolar concentrations of calmodulin activated the channel by increasing the open probability of single-cha nnel events in a dose dependent manner. The activatory effect of calmo dulin was reversed by 10 mu M ruthenium red. At 10(-5) M free [Ca2+], calmodulin (0.1-1 mu M) inhibited channel activity. Calmodulin overlay s were carried out using concentrations of Ca2+ similar to those used for the planar lipid bilayer assays. In the presence of 10(-7) M [Ca2], calmodulin bound to the ryanodine receptor, to a region defined by residues 2937-3225 and 3546-3655. These results suggest that calmoduli n may activate the Ca2+-release channel (ryanodine-receptor) by intera cting with binding sites localized in the central portion of the RYR p rotomer. (C) 1995 Academic Press, Inc.