kINETIC STUDIES OF THE EFFECT OF FKBP12 ON THE RYANODINE RECEPTOR FROM SKELETAL MUSCLE SARCOPLASMIC RETICULUM

Yasser Abdellatif, Do Han Kim, Kwangju Institute of Science and Technology, Kwangju, Korea.

FK506 binding proteins (FKBPs) are associated with ryanodine receptor (RyR) Ca²⁺ release release channels in the sarcoplasmic reticulum (SR) of skeletal and cardiac muscle. The 12kDa FKBP12 co-ordinates skeletal RyR channel opening¹, maintains EC coupling² and for interactions between parts of the DHPR and RyR³. FKBPs couple the gating of adjacent RyRs⁴ and may transmit signals between RyRs in vivo.

Our aim was to examine the effect of removing FKBP12 from RyRs (using rapamycin) on the Ca²⁺ handling by skeletal SR vesicles using stopped-flow spectrophotometry. SR vesicles were prepared from rabbit muscle following euthanasia by anaesthetic overdose. Ca²⁺ uptake by SR was slower after FKBP12 removal and RyRs showed an increased sensitivity to activation by caffeine and quercetin. Ca²⁺ release amplitude fell by ~46% with 2.5 mM caffeine, while the release rate doubled. The calcium release amplitude with 25 µM quercetin was not changed while the release rate fell by ~35%. FKBP12 removal did not affect SERCA Ca²⁺ ATPase activity. In conclusion, FKBP12 depletion led to (1) impaired capacity to adapt to increasing concentrations of either caffeine or quercetin (2) reduced response to caffeine and quercetin and (3) slower calcium uptake by SR.

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