FIGURE 9.

The left panel shows analysis of the initial rates of decrease in [Mg_tot] (initial Δ[Mg_tot]/Δt) in three myocytes which were loaded with Mg²⁺ to different levels of [Mg²⁺]_c (the same cells as used for the analysis in the left panel of Fig. 2). The initial Δ[Mg_tot]/Δt (the slopes of solid lines) estimated by linear regression to [Mg_tot] traces for 180 s (60–240 s after solution exchange) are indicated below the traces. The right panel compares initial Δ[Mg_tot]/Δt (open circles) and initial Δ[Mg²⁺]_c/Δt (solid circles) calculated through Steps 1–7 (see Appendix for details). A solid curve indicates the least-squares-fit to open circles by sum of the two Hill-type curves (see Eq. 2): two dotted curves marked “high” and “low” with the best-fitted parameter values are shown at the top of the panel.