The immunophilin FK506-binding protein modulates Ca2+ release channel closure in rat heart.
1. The nature of the signal that terminates the release of Ca2+ from the cardiac sarcoplasmic reticulum has remained elusive. This study was intended to examine whether FK506-binding protein (FKBP), which is tightly associated to the ryanodine receptor (RyR)/Ca2+ release channel, plays a role in the termination of Ca(2+)-induced Ca2+ release (CICR) in heart. 2. Confocal microscopy and the Ca2+ indicator fluo-3 were used to visualize the elementary release events, i.e. 'Ca2+ sparks' in rat ventricular myocytes under resting or voltage-clamped conditions. Additionally, electrophysiological single-channel recordings, at constant [Ca2+] or during [Ca2+] steps produced by photorelease of caged Ca2+, were obtained from rat cardiac RyRs incorporated in planar lipid bilayers. 3. Inhibition of FKBP by the immunosuppressants FK506 or rapamycin increased the duration of spontaneous or depolarization-evoked Ca2+ sparks 6- to 7-fold. In addition, Ca2+ sparks were seen with two-level amplitudes, corresponding to full and half normal spark amplitude. 4. FK506 potentiated and prolonged electrically stimulated [Ca2+]i transients and contractions, but did not affect the amplitude and kinetics of the L-type Ca2+ channel current. 5. In planar lipid bilayers, FK506 (15 microM) prolonged approximately 7-fold the mean open lifetime of reconstituted single RyRs, induced the appearance of long-lasting subconductance states, and markedly slowed the spontaneous decay of RyR activity elicited by fast and sustained Ca2+ stimuli. The time constant of the spontaneous decay of activity increased from 1.8 s in control to > or = 20 s in the presence of FK506. 6. We conclude that FKBP may afford an intrinsic mechanism to terminate RyR openings and it may thus exert a negative feedback on CICR in heart cells.
Xiao
R P
RP
Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA.
Valdivia
H H
HH
Bogdanov
K
K
Valdivia
C
C
Lakatta
E G
EG
Cheng
H
H
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D002148:Calmodulin-Binding Proteins / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism*; D007166:Immunosuppressive Agents / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects*; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000378:metabolism; D009124:Muscle Proteins / Q000378:metabolism; D009206:Myocardium / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011090:Polyenes / Q000494:pharmacology; D051381:Rats; D019837:Ryanodine Receptor Calcium Release Channel; D020123:Sirolimus; D022021:Tacrolimus Binding Proteins
D015220:Calcium Channels; D002148:Calmodulin-Binding Proteins; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D006360:Heat-Shock Proteins; D007166:Immunosuppressive Agents; D008051:Lipid Bilayers; D009124:Muscle Proteins; D011090:Polyenes; D019837:Ryanodine Receptor Calcium Release Channel; D022021:Tacrolimus Binding Proteins; D002118:Calcium; D020123:Sirolimus