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Biophys J, March 2002, p. 1266-1277, Vol. 82, No. 3

Effects of Quercetin on Single Ca2+ Release Channel Behavior of Skeletal Muscle

Eun Hui Lee,* Gerhard Meissner,dagger and Do Han Kim*

 *Department of Life Science, Kwangju Institute of Science and Technology (K-JIST), Kwangju 500-712, Korea; and  dagger Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599-7260, USA

Quercetin, a bioflavonoid, is known to affect Ca2+ fluxes in sarcoplasmic reticulum, although its direct effect on Ca2+ release channel (CRC) in sarcoplasmic reticulum has remained to be elucidated. The present study examined the effect of quercetin on the behavior of single skeletal CRC in planar lipid bilayer. The effect of caffeine was also studied for comparison. At very low [Ca2+]cis (80 pM), quercetin activated CRC marginally, whereas at elevated [Ca2+]cis (10 µM), both open probability (Po) and sensitivity to the drug increased markedly. Caffeine showed a similar tendency. Analysis of lifetimes for single CRC showed that quercetin and caffeine led to different mean open-time and closed-time constants and their proportions. Addition of 10 µM ryanodine to CRC activated by quercetin or caffeine led to the typical subconductance state (~54%) and a subsequent addition of 5 µM ruthenium red completely blocked CRC activity. When 6 µM quercetin and 3 mM caffeine were added together to the cis side of CRC, a time-dependent increase of Po was observed (from mode 1 (0.376 ± 0.043, n = 5) to mode 2 (0.854 ± 0.062, n = 5)). On the other hand, no further activation was observed when quercetin was added after caffeine. Quercetin affected only the ascending phase of the bell-shaped Ca2+ activation/inactivation curve, whereas caffeine affected both ascending and descending phases. [3H]ryanodine binding to sarcoplasmic reticulum showed that channel activity increased more by both quercetin and caffeine than by caffeine alone. These characteristic differences in the modes of activation of CRC by quercetin and caffeine suggest that the channel activation mechanisms and presumably the binding sites on CRC are different for the two drugs.

Biophys J, March 2002, p. 1266-1277, Vol. 82, No. 3
© 2002 by the Biophysical Society   0006-3495/02/03/1266/12  $2.00


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