The investigation of altered Ca2+ handling by the selective modulation of Ca2+ uptake rate of sarcoplasmic reticulum

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We investigated the role of the alteration of sarcoplasmic reticulum (SR) which is known to be a cause of cardiac dysfunction in failing heart. We used saponin-treated thin trabeculae obtained from mice hearts with overexpression of SR-Ca2+ ATPase (SERCA-TG) and sarcolipin (SLN-TG), respectively. Ca2+ uptake rate was faster in SERCA-TG and slower in SLN-TG. Maximal Ca2+ content, Ca2+ induced Ca2+ release and Ca2+ leak were not altered in SERCA-TG and SLN-TG. In the papillary muscle experiment using Ca2+ sensitive photoprotein aequorin, peak tension and peak amplitude of Ca2+ transient were increased in SERCA-TG and decreased in SLN-TG. Relaxation time of tension and decline of Ca2+ transient were accelerated in SERCA-TG and prolonged in SLN-TG. Thus, we concluded that selective modulation of Ca2+ uptake into SR influenced the amplitude and time course of Ca2+ transient and tension, however, it did not influence maximal Ca2+ content, Ca2+ induced Ca2+ release and Ca2+ leak of SR.