| First Author | Szentesi P | Year | 2004 |
| Journal | Circ Res | Volume | 95 |
| Issue | 8 | Pages | 807-13 |
| PubMed ID | 15388639 | Mgi Jnum | J:103488 |
| Mgi Id | MGI:3609579 | Doi | 10.1161/01.RES.0000146029.80463.7d |
| Citation | Szentesi P, et al. (2004) Sarcoplasmic reticulum Ca2+ refilling controls recovery from Ca2+-induced Ca2+ release refractoriness in heart muscle. Circ Res 95(8):807-13 |
| abstractText | In cardiac muscle Ca2+-induced Ca2+ release (CICR) from the sarcoplasmic reticulum (SR) is initiated by Ca2+ influx via L-type Ca2+ channels. At present, the mechanisms underlying termination of SR Ca2+ release, which are required to ensure stable excitation-contraction coupling cycles, are not precisely known. However, the same mechanism leading to refractoriness of SR Ca2+ release could also be responsible for the termination of CICR. To examine the refractoriness of SR Ca2+ release, we analyzed Na+-Ca2+ exchange currents reflecting cytosolic Ca2+ signals induced by UV-laser flash-photolysis of caged Ca2+. Pairs of UV flashes were applied at various intervals to examine the time course of recovery from CICR refractoriness. In cardiomyocytes isolated from guinea-pigs and mice, beta-adrenergic stimulation with isoproterenol-accelerated recovery from refractoriness by approximately 2-fold. Application of cyclopiazonic acid at moderate concentrations (<10 micromol/L) slowed down recovery from refractoriness in a dose-dependent manner. Compared with cells from wild-type littermates, those from phospholamban knockout (PLB-KO) mice exhibited almost 5-fold accelerated recovery from refractoriness. Our results suggest that SR Ca2+ refilling mediated by the SR Ca2+-pump corresponds to the rate-limiting step for recovery from CICR refractoriness. Thus, the Ca2+ sensitivity of CICR appears to be regulated by SR Ca2+ content, possibly resulting from a change in the steady-state Ca2+ sensitivity and in the gating kinetics of the SR Ca2+ release channels (ryanodine receptors). During Ca2+ release, the concomitant reduction in Ca2+ sensitivity of the ryanodine receptors might also underlie Ca2+ spark termination by deactivation. |
