Table 3.

Relative ratios of ion fluxes of exchangers, pumps, and sarcoplasmic reticulum (SR) Ca²⁺ kinetics

Current	EE	Ref.	LE	Ref.	N	Ref.
Na+/Ca2+ exchange	4.95	Liu et al. (2002)	1.74	Liu et al. (2002), Artman (1992)	1.00	Liu et al. (2002), Artman et al. (1995), Artman (1992)
SR Ca2+ pump	0.03	Liu et al. (2002)	0.21	Liu et al. (2002), Chen et al. (2000)	0.21	Liu et al. (2002), Chen et al. (2000)
RyR channel	0.05	Liu et al. (2002)	0.40	Liu et al. (2002)	0.40	Liu et al. (2002)
SR transfer	0.04	Liu et al. (2002)	0.30	Liu et al. (2002)	0.30	Liu et al. (2002)
SR leak	0.04	Liu et al. (2002)	0.30	Liu et al. (2002)	0.30	Liu et al. (2002)

Developmental change in Na⁺/Ca²⁺ exchange (I_NaCa) is reported as I–V curves in both the rabbit and guinea pig (Artman et al. 1995) and by Western blots of NCX1 protein in the mouse (Liu et al. 2002) and rabbit (Artman 1992); on the basis of the literature implying that postnatal quantitative changes in the density of I_NaCa are in good agreement with the changes in protein production level, we assumed that the relative production level of the proteins directly reflected the relative ratios of ion fluxes of I_NaCa, the SR Ca²⁺ pump (I_SR,uptake), and the RyR channel (I_RyR). Hence, we computed the relative ratios of the current fluxes from Western blots of SR-related proteins (Liu et al. 2002; Chen et al. 2000). The average relative production levels of SR-related proteins in the EE stage (0.04), LE stage (0.30), and N stage (0.30) were adopted as the relative activities of I_SR,transfer and I_SR,leak at these stages