Résumé
Ryanodine receptors/Ca 2+ -release channels (RyR2) from the sarcoplasmic reticulum (SR) provide the Ca 2+ required for contraction at each cardiac twitch. RyR2 are regulated by a variety of proteins, including the immunophilin FK506 binding protein (FKBP12.6). FKBP12.6 seems to be important for coupled gating of RyR2 and its deficit and alteration may be involved in heart failure. The role of FKBP12.6 on Ca 2+ release has not been analyzed directly, but rather it was inferred from the effects of immunophilins, such us FK506 and rapamycin, which, among other effects, dissociates FKBP12.6 from the RyR2. Here, we investigated directly the effects of FKBP12.6 on local (Ca 2+ sparks) and global {intracellular Ca 2+ concentration ([Ca 2+ ] i ) transients} Ca 2+ release in single rat cardiac myocytes. The FKBP12.6 gene was transfected in single myocytes using the adenovirus technique with a reporter gene strategy based on green fluorescent protein (GFP) to check out the success of transfections. Control myocytes were transfected with only GFP (Ad-GFP). Rhod-2 was used as the Ca 2+ indicator, and cells were viewed with a confocal microscope. We found that overexpression of FKBP12.6 decreases the occurrence, amplitude, duration, and width of spontaneous Ca 2+ sparks. FK506 had diametrically opposed effects. However, overexpression of FKBP12.6 increased the [Ca 2+ ] i transient amplitude and accelerated its decay in field-stimulated cells. The associated cell shortening was increased. SR Ca 2+ load, estimated by rapid caffeine application, was increased. In conclusion, FKBP12.6 overexpression decreases spontaneous Ca 2+ sparks but increases [Ca 2+ ] i transients, in relation with enhanced SR Ca 2+ load, therefore improving excitation-contraction coupling.